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1. Historical review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2. Specifics of welding aluminium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852.1 The oxide film . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852.2 Solubility of hydrogen in the fused metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862.3 Physical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 862.4 The heat affected zone (HAZ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 872.5 Weldable aluminium alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3. Implications for the design and execution of welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893.1 Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893.2 Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.3 Controlling distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903.4 Use in the fabrication of a section with stiffeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4. Arc welding processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.1 TIG welding (Tungsten Inert Gas) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 934.2 MIG welding (Metal Inert Gas) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944.3 Synergic pulsed MIG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 944.4 "Spray MODAL" synergic MIG with modulated current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964.5 Filler wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5. Storage of semi-finished products and filler wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6. Surface preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7. Joint preparation and setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
8. Filler metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
9. Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1009.1 Repair of defective welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1019.2 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1029.3 Correcting distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1029.4 Flush dressing of the weld . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1029.5 Shot-peening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
10. Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10310.1 Approval procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10310.2 Testing welded joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
11. Weld imperfections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10311.1 Common weld imperfections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10411.2 Effect of weld imperfections on fatigue strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
12. Repairs and fittings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
13. Laser welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10613.1 Principle of the laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10613.2 Welding lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10613.3 Laser welding of aluminium alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10713.4 Laser weldability of aluminium alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
14. Friction Stir Welding (FSW) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10814.1 Principle of friction stir welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10814.2 Microstructure of the FSW joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10814.3 Comparisons with arc welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10914.4 Possibilities of welding with FSW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11014.5 Performance of FSW welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
15. Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
C h a p t e r 6W E L D I N G
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W ELDING is the process bywhich two or more parts
are joined by localised fusion ofthe metal to form a single com-ponent; the original contours ofthe initial parts disappear afterassembly.
Arc welding is still by far the mostwidespread joining process andthe one used most frequently inshipbuilding.
Technical advances in arc weld-ing with pulsed MIG havehelped improve the perform-ance of welding machines andthe quality of the weldmentsproduced.
The development of other processessuch as laser beam welding or fric-tion stir welding (FSW) will furtheradvance the design and fabricationof aluminium sub-assemblies forshipbuilding.
Whatever the welding techniquethat is used, the quality of work-manship of aluminium alloy weld-ments becomes increasinglyimportant on very long ships as itdetermines the fatigue resistanceof the most stressed areas of thevessel. The weld is a vital elementin the fatigue strength of anassembly.
1.HISTORICAL REVIEW
The first attempts at welding alu-minium were made in 1904, andgas welding was used at thattime [1].
Up until the early Sixties, weldingwith the oxy-acetylene torch wasthe only method available for weld-ing aluminium alloys. The use ofthis process was limited to flatwelding and thin sheet.
For many years the presence of anatural oxide film on the surface ofaluminium was a major obstacle tothe welding of this metal. For alu-minium to be welded correctly,this film must be removed andprevented from re-forming byshielding the weld pool from thesurrounding atmosphere.
In oxy-acetylene welding, fluxesin the form of paste diluted inwater were deposited on theedges to be welded and on thefiller wire to eliminate the oxidefilm. These fluxes were based onchlorides and fluorides. To avoidany risk of corrosion from fluxresidues, these had to beremoved by brushing or washingin water.
As with the arc welding of steel,rods of filler metal coated in fluxfor welding thicker productsbegan to become available from1925 onwards. One of the veryfirst known applications of arcwelding using coated rods camein France in 1934 with the con-struction of railway vehicles in5056 (A-G5) alloy for the ‘CieFrançaise des Chemins de Fer duNord’ [2]. This process was notdeveloped to any great extentowing to the unsatisfactory qual-ity of the weldments.
The first attempts at arc welding ina shielding gas (argon or helium)were made in the middle of theNineteen Thirties [3]. This techniquerepresented a major step forward,and eliminated the need for fluxwith its attendant risks of corro-sion. It was now possible to weldat high speed and in all positions,making aluminium a “fullyfledged” fabrication metal in itsown right.
The industrial development of theTIG and MIG processes began inthe early Fifties and advances andimprovements in these processeshave been made ever since. Onesuch innovation came at the begin-ning of the Nineties with electroni-cally controlled pulsed MIG welding.
6 . W E L D I N G
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WELDING A HATCHWAY FRAME
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Up until the early Sixties, shipsmade from aluminium alloys – aswell as aluminium alloy equipmenton steel ships (superstructures,funnels etc.) – were assembled bymeans of riveting, as indeed steelships still were.
The sailing ship “Morag Mhor”, a70 foot ketch made from alumi-nium-magnesium alloy (4 and 5%magnesium) and designed by aBritish naval architect, was thefirst known boat to be constructedwith MIG welding in 1953 [4].
2.SPECIFICS OF WELDINGALUMINIUM
Although the techniques used forwelding semi-finished productsmade from aluminium alloys arevery similar to and even the sameas those used for carbon steel, theoperating conditions are ratherdifferent. This is due to thepresence of the oxide film (Al2O3)on the surface of the metal (1) andto the physical properties ofaluminium alloys which are verydifferent from those of steels(table 47, p. 87).
2.1The oxide film
The natural film of oxide whichpermanently covers the surface ofthe metal is 50 to 100 nanometersthick. Its melting point is very high,2052°C, and it is insoluble in solidor liquid aluminium.
For welding purposes the filmmust be removed (2) andprevented from re-forming whilethe filler metal is being applied tothe weld seam (3). This is whyaluminium must be arc welded orlaser welded in a controlledatmosphere consisting of an inertgas such as argon, helium or theirmixtures.
Although the film is chemicallystable (it is an oxide) it neverthelessreacts with its environment byadsorbing traces of rolling mill oils,shaping lubricants and themoisture present in the air. All ofthese elements are sources ofhydrogen (4) when they aredissociated in the plasma of theelectric arc.
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(1) Cf. Chapter 10.
(2) In arc welding with the continuousTIG process, the welded piece is alwaysconnected to the minus pole (–) toremove the oxide film.
(3) Although it is an electrical insulator,the film is too thin to stop the flow ofelectrical current in the same way aslayers of anodising whose thickness iscommonly 15 to 20 microns.
(4) Greases and lubricants are carbonchains with the general formula CnH2nO.
LNG CARRIERS
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2.2Solubility of hydrogen in the fused metal
Given the very high solubility ofhydrogen in liquid aluminium, itdissolves in the weld pool of theweld seam as it is formed (figure60) (5).
However since hydrogen is notsoluble in solid aluminium, ifcooling is too fast it will have atendency to become trapped in themetal forming bubbles that will beporosities in the weld seam (6).
This is why it is so important toremove all possible sources ofhydrogen on the metal that arepresent in moisture, in traces ofgrease and in the shielding gases.
2.3Physical properties
Table 47 presents a comparativelist of those physical properties ofaluminium and steel which affectthe welding of these metals. It isthe thermal properties whichaccount for the significant differ-ences between the welding condi-tions for aluminium comparedwith those for steel.
Aluminium has a high calorificcapacity (899 J.kg-1.K-1, comparedwith 420 for steel) and a higher ther-mal conductivity (229 W.m-1.K-1,against 54 for steel). This meansthat much of the energy inputfrom the arc is used to heat up thepieces that are to be welded.
Aluminium’s high effusivity (7)requires a very high level of weld-ing energy. All other things beingequal, the rise in temperature ofaluminium parts to be welded willbe greater than for steel parts.
Heat quickly dissipates in alu-minium due to its high diffusivity(8) (0.9 compared with 0.2 forsteel), and this must be compen-sated by the input of heat from theelectric arc.
Aluminium’s high coefficient ofexpansion (23.10-6K-1), its high dif-fusivity and the metal’s high levelof temperature mean that weldingis accompanied by more strain inaluminium than in other metals.
To maintain stable conditionstherefore, aluminium must bewelded at a rate higher than therate at which the heat is propa-gated (figure 61).
If carbon steels are cooled tooquickly they undergo a martensitictransformation that is accompa-nied by an increase in volumewhich in turn can cause cracks atthe base of the weld seam.
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SOLUBILITY OF HYDROGEN
50
0,7
0,036
660 2500
Melting point
Boiling point
Sol
ubili
tyof
hydr
ogen
(incm
3 /10
0g
met
al)
Solubility in liquid aluminium
Solubility in solid aluminium
Figure 60
(5) Contrary to what happens withcertain steels, hydrogen does notembrittle aluminium and does notsensitise it to stress corrosion.
(6) Cf. table 54, pp. 104-105.
(7) Effusivity “b” is the product of the square root of the product of thermal conductivity λ by density ρand by specific heat capacity Cp :b = :λ.ρ.Cp.
This variable describes the amount ofheat which a heated zone receives byconduction, where: λ = thermal conductivityρ = densityCp = calorific capacity.
(8) Thermal diffusivity “a” is defined bythe relation a = λ
ρ. Cp
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There are no such changes withaluminium alloys. As a result, therapid cooling rate of the weld –between 100 and 1000°C persecond – does not cause anydefect in the seam.
It is therefore not normallynecessary to preheat aluminiumprior to welding as can be donewith steel (to prevent cracks in theweldment during cooling).
All of these factors must beallowed for when designing jointsand executing the actual welds.This highly important aspect isdiscussed in Section 3.
2.4The heat affectedzone (HAZ)
With steels, changes of phasecause local hardening of the heataffected zone over a width ofseveral millimetres. In contrast,the effect of heating is to softenaluminium alloys when they are: n in the strain hardened conditionas is the case with the 5000 seriesalloys in the H116, H24, H32 andH34 tempers,n thermally treated, e.g. 6000series alloys in the T5 or T6 tem-pers.
As figure 62, p. 88, shows, thematerial’s mechanical propertieschange gradually from the weldseam outward to the edges of theHAZ (9).
As a result, the mechanicalproperties of the weldment areusually inferior to those of theparent metal. They are near to theannealed condition for strainhardened alloys and to the T4temper for age hardening alloys.
6. WELDING
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PHYSICAL PROPERTIES OF ALUMINIUM AND STEEL E24
Property Unalloyed Aluminium (1050A) Steel E24 Ratio Al/Steel
Fusion interval (°C) 645/658 1 400/1 530
Melting point of oxides (°C) 2 052 900
Solidification shrinkage (%) 1,7 1,2 1,4
Density (kg.m-3) 2 700 7 820 0,34
Mass heat capacity Cp (J.kg-1.K-1) 899 420 2,14
Latent heat of fusion (kJ.kg-1) 385 210 1,83
Thermal conductivity (W.m-1.K-1) 229 54 4,24
Thermal diffusivity "a" (10-4.m2.sec-1) 0,9 0,2 4,5
Effusivity "b" (J. m-2.K-1.sec -1/2) 24 000 16 000 1,5
Coefficient of linear expansion α (10-6.K-1) 23,5 13,5 1,74
Electrical resistivity ρ (10-9 Ω.m) 292 1010 0,29
Young’s modulus (MPa) 70 000 210 000 0,33
HEAT FLOW DURING WELDING
z
x
y
θy3
θy2
θy1
θy0
Welding directionäMaximum
temperature level
ä
θx0θx1θx2
Table 47
Figure 61
(9) The mechanical properties of theweld seam itself are usually superior tothose of the HAZ. When there is a crack,this usually occurs outside the weldseam.
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This is why for stress calculations,the design codes and regulationsof the classification societiesspecify levels of yield strength ofthe annealed condition for strainhardening alloys and of the T4temper for age hardening alloys.
In the case of butt welds, the HAZis some 25 mm wide either side ofthe weld seam whatever thethickness of the parent metal andwhether TIG or MIG welding isused.
The impact on the mechanicalproperties of the weldment mustbe minimised by: selecting the filler metal that isbest suited to the parent alloy, establishing a welding cycle thatis as rapid as possible to limit thesize of the HAZ, designing the assembly so thatthe weldments are in the leaststressed positions.
2.5Weldable aluminium alloys
Most of the alloys belonging to the1000, 3000, 5000 and 6000 seriescan be welded with the conven-tional TIG or MIG processes and bythe other energy beam processes– electron beam, laser etc.
The 5000 series is the one that ismost suitable for welding.
The wrought alloys containing cop-per in the 2000 and 7000 series(10) are not easy to arc weld (11).The presence of the coppercauses cracking and shrinkagecracks on the weld seam.
The weldability of castingsdepends more on the method ofcasting than on the chemical com-position of the alloy. Diecast partscannot be welded as they maycontain a lot of air that is intro-duced during the casting process.
Sand cast or chill cast parts can bewelded provided they are “clean”,i.e. free from porosities and shrinkholes that produce blisters in theweld seam (12).
The 42100 (A-S7G) and 43300 (A-S10G) alloys can be welded withalloys in the 6000 series (13).
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HAZ
MECHANICAL CHARACTERISTICS OF THE HAZ
Rp 0,
2
Figure 62
(10) The 7000 alloys without copper suchas the 7020 can be welded but the HAZis very sensitive to exfoliating corrosion(cf. Chapter 10).
(11) The welding regulations andconstruction codes such as Eurocode 9and standard BS 8118 actually excludethese alloys from arc weldedassemblies.
(12) Porosities in sand castings can beavoided by the use of metal heat sinksthat improve the microstructure andprevent the formation of porosity.<0
(13) The 5000 series cannot be weldedwith the 42000.
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3.IMPLICATIONS FOR THE DESIGNAND EXECUTION OF WELDS
During welding, every point on awelded piece undergoes a heatcycle whose profile is a function ofa number of parameters: the power of the heat sourcewhich depends on the process(MIG, TIG etc.), the geometry of the piece, the welding position (flat, verti-cal, horizontal, overhead), the diffusion coefficient of thematerial.
The result is a variety of differenttemperatures present in thecomponent in the course ofwelding. These temperaturedifferences translate into residualdistortions of varying extent andwhich are due: to differences in expansion, to shrinkage as the weld seamsolidifies.
3.1Distortion
Distortion can be longitudinal ortransverse:
longitudinal distortion is cau-sed by the contraction of themetal during the process ofcooling which is not uniform.Stresses are set up along the weldseam (figure 63). These stresses depend on theposition of the weld – they areminimal or non-existent when theweld is on or near the neutral axisof the piece (figure 64) but verypronounced when the weld isasymmetrical. Concavity willfollow the same orientation as theweld seams. On long components,distortion may manifest itself as atwist that will prove difficult tocorrect (figure 65).
As a general rule, distortion will besignificant when the weld seams areasymmetrical relative to the piece.
transverse distortion is due toa shortening of the weld seam –this is more pronounced at thesurface of the seam than at itsroot and so creates a ‘gripping’effect with angular deformation(figure 66).
This effect must be limited bybalancing the stresses with asecond weld: a double vee-grooveweld on thick components and onthe opposite side for fillet welds(figure 67).
6. WELDING
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LONGITUDINAL DISTORTION
WELDS ON THE NEUTRAL AXIS
ASYMMETRICAL WELDS
DISTORTION OF WELDS
CORRECTION OF DISTORTION
Figure 63
Figure 64
Figure 65
Figure 66
Figure 67
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3.2Stresses
Local levels of stress can exceedthe yield strength of the metal,and are a function of: the shape of the piece, the layout of the weld seams, the weld sequence, positioning tools, clamping.
Figure 68 indicates the level oflongitudinal residual stress insections fabricated by welding.
3.3Controlling distortion
There are a number of factors bywhich distortion can be controlled:
Joint configuration: so far aspossible the designer should posi-tion the welds in a plane of sym-metry of the component and onits neutral axes (14), and use spe-cially designed shapes (15) wherepossible.
Careful forming must be usedto minimise clearances and off-sets between the welded compo-nents and to eliminate fitup errors,
The welding sequence: it isimportant to weld moving towardsthe outside edges to allow expan-sion to occur freely. The weldsmust be executed in reverse orderof length, with the shortest first tobetter distribute any distortion.Distortion can be corrected moreeasily with long seams (figure 69).
Where possible, automaticwelding with two torches is a verygood way of reducing distortion(figure 70).
The distribution of internalstresses can be optimised byusing a sequence of welds that
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Connection of plates in 5083 H111 and extruded shapes in 6082 T6
Upper flange
Lower flange
Web
RESIDUAL STRESSES
Figure 68
WELD SEQUENCE
2 3
11
243
Start ofweld
Figure 69
YACHT FRAME
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WELDING WITH TWO TORCHES
Torch
Torch
Figure 70
BUTT WELDINGSHAPES
2
3
1
Weld sequence: 1, 2, 3
Figure 71
6. WELDING
induces residual compressionstresses in the weld seams thatare stressed in tension (figure 71).This approach will verysignificantly improve the fatiguestrength of the welded joints.
The purpose of clamping is tohold the parts in position.However clamps, fixtures etc.must not prevent expansion onthe longest axes or componentswill be stressed (with an attendantrisk of softening due to expansion∆l). Generally speaking, partsshould not be clamped in thedirections of greatest expansionas this will aggravate distortionsquare to the weld (figure 72).
On thick material, angular distortioncan be avoided by attachingtemporary stiffeners across theweld (figure 73).
Welding parameters: Distor-tion can also be caused by thesolidification shrinkage of theweld seam. The greater the quan-tity of fused metal and the higherthe temperature, the greater thisshrinkage will be. Distortion canbe limited by using high energyheat sources to weld as rapidlyas possible – the faster the wel-ding, the less time the heat hasto dissipate
Balance of heat flows: Long-itudinal distortion can be aggrava-ted by a thermal imbalance bet-ween the welded pieces. Thisimbalance can be due to:- the very different masses of thepieces that are to be joined,- misalignment as the weldingtorch moves, - poor contact with the support, - etc.
Whenever possible therefore, the“thermal masses” must be bal-anced to achieve good thermal sym-metry in the assembly (figure 74).
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EFFECT OF CLAMPING
L0 = Initial lengthL1 = Final length
L0
L1
-∆l
-∆l
CLAMPING WITH STIFFENERSACROSS THE WELD
THERMAL BALANCEOF A WELD
Figure 72 Figure 73Figure 74
(14) This layout has a positive influenceon the fatigue behaviour of the weldedassembly, cf. Chapter 4.
(15) Cf. Figures 11 to 14, Chapter 2.
Compression
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3.4Use in the fabricationof a section with stiffeners
Figure 76 shows the optimumwelding sequence (i.e. order inwhich the welds are made) for
limiting distortion when weldingthe elements of the sectionillustrated in figure 75.
Welding starts in the centre of thepanel and moves out towards thefree edges to allow unimpededexpansion.
92
TYPICAL WELDING SEQUENCE OF A PANEL
19ää
ä
30 20 18
48
9 10 11 31
29
40
17
38 37 36 33 34 35 39
16 15 12 13 14 32
2827
2526
13
57
2322
2124
47
ää
ä
ä ä
ä
ä ä ä
ääää
24
68
PANEL WITH STIFFENERS
Frame
Stiffener
Skin
ä
ä
ä
Figure 76
Figure 75
46 45 44 41 42 43
LIFTING ALUMINIUM SUB-ASSEMBLIES
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4.ARC WELDING PROCESSES
In arc welding, the joint betweenthe pieces to be assembled ismade by filling an appropriateshape (Vee, cross, bell) with a fillermetal (rod or wire) which is meltedstep by step. The joint can be filledin one or more passes. As the fillermetal melts, so do the edges ofthe components that are beingjoined together (unlike in brazing).
Ever since the arc welding ofaluminium in inert gases (argon orhelium) came into widespreadindustrial use, there have alwaysbeen two main processes but theytend to complement rather thancompete with one another (table48, p. 97). One, TIG, is mainlymanual, while the other, MIG, canbe fully automated. MIG weldinghas advanced in great stridessince the early Nineties to thepoint where the conditions underwhich aluminium is welded arenow greatly enhanced.
The mechanical properties of theweld seams are identical in bothprocesses, all other things beingequal, i.e. parent alloy, filler metaland material thickness.
4.1TIG welding(Tungsten Inert Gas)
In TIG welding (16), the electric arcforms between a refractorytungsten electrode and the pieceto be welded. The shielding gas –usually argon – is blown outthrough the nozzle of the torch(figure 77).
In manual TIG welding, the fillermetal in the form of a straightenedwire rod (0.8 mm to 4.0 mm indiameter) is held manually by thewelder. In automated TIG welding,the filler metal is fed automatically
from a reel of wire of diameter0.8 mm to 2.0 mm by a motoriseddispenser.
Welding machines operate withstabilised HF alternating currentfor manual welding or continuousor pulsed d.c. current forautomatic welding. Machinesmust be fitted with an electroniccircuit board designed foraluminium welding, with a pulsearc stabiliser and an arc re-igniter.
The geometry of the refractoryelectrodes is an important factorinfluencing the quality of the weld.The electrode must be groundsharp unless the welding machineruns on a.c. current. For d.c.current, the electrode tip must beinside a cone of 30 to 60 degrees,and machining (or grinding) marksmust run parallel to thelongitudinal axis of the electrode(figure 78).
6. WELDING
93
PRINCIPLE OF TIG WELDING
Welding torchCurrent input
Argon gas inlet
Water return
Shielding gas
Gaseous atmosphere
Solidified metal
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Direction of welding
Nozzle
Filler metal
Base metal
Tungstenelectrode
Cooling water inlet
GRINDING OF TIG ELECTRODES
GOOD BAD BAD
Correctelectrode
Currenttoo high
Contaminatedelectrode
30 à 60°
TIG continuousA.C.TIG
Figure 78
Figure 77
(16) The process is known as WIG inGermany (tungsten in German is‘Wolfram’) and GTAW in America (GasTungsten Arc Welding).
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TIG uses less power than MIG,so the heat affected zone iswider (because of the diffusioncoefficient) and there is moredistortion due to expansion. Therate of welding which is controlledby the welder is relatively slow, inthe region of 0.2 m.min-1.
TIG welding is above all a manualprocess and simple to use,allowing meticulous workmanshipand precision results.
Welding is possible in all positions.It is suitable for material 1 to 6 mmthick. It can be used to weld withclearances that are over twice thethickness of components under1.5 mm thick.
TIG is difficult to automate so islimited to use in the developmentof prototypes and in the repair ofdefective welds.
4.2MIG welding (Metal Inert Gas)
In MIG welding (17), the filler wirealso acts as the electrodesupplying the power (figure 79).The wire is automatically uncoiledfrom a reel and fed to the weldingtool (gun or torch) as it is used up.
The welding power is proportionalto the amount of wire that is fed tothe weld seam, and is supplied bya d.c. power source which can becontinuous or pulsed. Connectionis made with reverse polarity, i.e.the workpiece is always con-nected to the minus (negative) poleto ensure descaling of the oxidefilm.
MIG welding is ‘self-pickling’because the transfer of electronsfrom the workpiece to the fillerwire breaks the oxide film(provided it is very thin, severalnanometers).
A thick oxide layer that has formedfollowing long exposure toambient humidity cannot be fully
removed, and the weld seam willhave oxide inclusions (defect 303,cf table 54, p. 104). Semi-finishedproducts should therefore bestored under cover in a dry place(18).
The welding current varies from40 to 700 Amps depending on anumber of parameters such as thediameter of the filler wire, theposition of the weld, the size ofthe components etc.
The classic MIG process usingcontinuous current has manyadvantages: excellent productivity due to thehigh rate of filler metal deposition, good penetration, low splatter, the process can be automated.
4.3Synergic pulsed MIG
MIG welding has made greatadvances since the appearance inthe early Eighties of so-called“synergic pulsed current” genera-tors in which the current is sup-plied by power transistors.
Prior to this, power was suppliedby thyristor generators whosepulse frequency was a direct func-tion of the mains frequency.Settings were difficult and lackedflexibility because the speed ofthe wire had to be adjustedaccording to the frequency.
Synergic pulsed current genera-tors allow the welding cycle to beregulated (figure 80) to give: high current at the start of theweld to avoid lack of fusion andpenetration, and low current at the end of theweld to prevent crater formation.
94
PRINCIPLE OF MIG WELDING
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Welding torch
Nozzle
Contact tube
Electrode wire
Gaseous atmosphere
Base metalSolidified metal
Molten metal
Electric arcShielding gas
Positive polarity(+) at the electrode
Figure 79
(17) Still also known as MAG (MetalActive Gas) or GMAW (Gas Metal ArcWelding).
(18) Cf. Section 5.
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6. WELDING
The welder can control threeparameters to optimise the weldseam: the speed of the wire, propor-tional to the welding current, the welding speed, the height of the arc, proportio-nal to the welding voltage.
With these machines, theparameters adjust automatically tothe displayed speed of the wire.Settings can be refined byadjusting the height of the arc.
In this system, the metal istransferred “drop by drop” (i.e.
one drop of metal per pulse),allowing the minimum weldablethickness to be reduced from 3 toaround 1 mm (19).
Pulsed MIG offers a number ofadditional benefits overconventional MIG welding withcontinuous current: welds can be made in any posi-tion, distortion is limited (low powerinput), limited weld repairs and fewer innumber, wide range of thicknesses withthe same diameter wire,
good joint quality and goodmechanical properties, good appearance of the weldseam, especially with spraytransfer, process can be fully automated.
95
SYNERGIC WELDING CYCLE
> 700 Aoverco-mes the aluminalayer
Welding currentStriking ls peak
Start-up current
(hot start)Welding current
Crater filler
current
time
Good penetration
from the start
(avoids incipient
fracture)
No crater at the
end of the bead
(avoid cracking)
From Air Liquide Welding
Figure 80
(19) With the old-type generators thetransfer of metal by spraying was onlypossible at 20 V and over. Below thisvoltage, globule or short-circuit transferis unsuited to the welding of aluminium,which accounts for the minimumthickness of 3 mm.
Time
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4.4“Spray MODAL”synergic MIG withmodulated current
There is now a variant of thesynergic welding technique – the“Spray Modal” process (20). Itoperates with modulated currentwhich falls very rapidly over a veryshort period of time (severalmilliseconds) with every pulseduring which several drops of fillerare projected into the weld pool(figure 81). These rapid variationsin voltage within the arc cause theweld pool to vibrate, encouragingthe evacuation of hydrogenbubbles from the metal while it isstill liquid.
Compared with synergic pulsedMIG, Spray-MODAL welding reduces or even eliminatesporosity in the weld (figure 82). enhances penetration, increases welding speed.
4.5Filler wires
An evenly dispensed filler wire willensure good arc stability andhence the quality of the weld.
The low rigidity of the filler wiresrequires the use of suitable
dispensers to minimise thechances of the wire snagging inthe torch tube which must bemade of PTFE (“Teflon”) toeliminate risks of abrasion.
A torch with a push/pull wiredispensing system is recom-mended to ensure optimumdispensing regularity, especiallywhen using the 4043A wire gradeand in automated welding.
Filler wire is usually 1.2 mm indiameter, although there are also1.6 mm gauge wires; these aremore rigid and their use is growingwith pulse MIG. They are alsoused when the rate of depositionis high.
Shaving the filler wires in the finaldrawing pass has a number ofeffects, all of which enhance thequality of the weld: it eliminates the outer zonewhich can be the site of magne-sium segregation, it removes traces of grease, it ‘sizes’ the weld which removessurface irregularities that are areasof moisture retention (figure 83).
96
THE SPRAY-MODAL PROCESS
MIG PULSED CURRENT
Frequency
Background current
Pulse voltage
MIG SPRAY MODAL - SAFFrequency
Spray current
Weldingvoltage
Background current
MIG pulsed current Spray MODALTM
Average current
±10 drops perpulse
1 drop perpulse
Figure 81
EFFECT OF SPRAY-MODAL ON POROSITY
Spray Arc
Spray MODALTMPoro
sity
sur
face
(mm
2 )fo
r a
100
mm
wel
d be
ad
Wire speed in cm/min
25
20
15
10
5
025 30 35 40 45
Welding conditions:
• part: part in 5456A - thickness 10 mm• wire: wire in 5356 - diameter 1,2 mm• H2: 2000 ppm• I: 216 A• U: 23 V• wire speed: 12,5 m/min
From Air liquide Welding
Figure 82
GX50
From Air liquide Welding
SURFACE CONDITIONOF FILLER WIRES
Figure 83
(20) Patented by Air Liquide.
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6. WELDING
5.STORAGE OF SEMI-FINISHEDPRODUCTS AND FILLER WIRE
Given aluminium’s very strongaffinity for hydrogen when in theliquid state (figure 60, p. 86), it isessential to remove all possiblesources of that element, especiallymoisture which can deposit onsemis and filler wire in storage andhydrate the oxide layer.
Filler wire is always supplied insealed packs that must be storedin an enclosed, covered roomthat is at the same temperatureas the welding shop. The packsshould not be opened untilrequired for use.
When welding operations arecomplete, any wire left on the reelmust be stored in a cabinetmaintained at a constant 40°C. 97
PARAMETERS OF TIG AND MIGWELDING
Thickness 1 mm andover, in several passes ifnecessary
All welded fabrications
Thickness 1 to 6 mm
Prototypes
Repairing defective welds
Thickness 0.1 to 10 mm
Automated welding withgood weld quality
Application
Faster: 0.40 to 1 m/min-1Slow: 0.15 to 0.30 m/min-10.30 to 0.60 m/min-1Welding speed
Argon or a mixture of 30%argon, 70% helium (*), (**)
Flow 1 l/min-1 for a nozzle18 to 25 mm in diameter
Argon or mixture of 70%argon, 30% helium(*)
Flow 10 l/min-1
HeliumGas
80° in the direction ofmotion
80° in the direction ofadvance
80° in the direction ofadvance
Torch angle
Filler wirePure tungstenZirconium tungstenElectrodes
Direct, with very shallowtrailing edge. A pulsedsource is a good option forslender work.
Alternating with HF andarc decay (speciallydesigned for aluminiumalloys).
DirectCurrent source
d.c. MIGa.c. TIGd.c. TIG
(*) The helium in argon/helium mixtures increases the welding speed and improves penetration. Table 48(**) Pulse MIG and Spray MODAL™ synergic MIG methods operate mainly with argon.
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6.SURFACEPREPARATION
Other sources of hydrogen are therolling and forming greases andoils left on the surface of themetal, and other impurities of dif-ferent types, such as traces ofpaint.
The surface of the metal musttherefore be cleaned very carefullyon both sides, starting by degreas-ing with a non-chlorinated solventto dissolve the greases and oils(21). Solvents are themselveshydrocarbon compounds contain-ing hydrogen atoms, so great caremust be taken to ensure no traceis left prior to welding.
After degreasing, the edges mustbe brushed (after chamfering asnecessary) on both sides of themetal and over a sufficient widththat is at least equal to the widthof the heat affected zone, i.e. 25mm. A rotary brush with stainlesssteel wires should be used forthis.
Whatever method of brushing isused (manual or mechanical) thebrush itself must be very cleanand operators must wear gloves.
The “life” of surface preparation iscertainly no more than one day,after which time the oxide filmmay well absorb moisture oncemore, especially in humid environ-ments (22).
To eliminate moisture, just prior towelding an oxy-acetylene torchcan be used to pre-heat the edgesat a temperature above dew pointin the region of 30 to 40°C.
7.JOINT PREPARATION AND SETUP
These operations are veryimportant, and will determinethe quality of the weld and itsfatigue resistance. For example,excessive clearance betweenthe workpieces can cause theweld seam to collapse and leadto the formation of undercutsthat can be very detrimental tothe quality of the weld and itsfatigue resistance.
The type of edge preparation willdepend on: the thickness of the work, the type of weld: butt, flat or fillet,vertical, overhead or horizontal, the use of a backing strip or bar,whether permanent or not.
As a general rule, the edges ofmaterial up to 4 mm thick are notchamfered.
Ideally, edges that are to bewelded should be prepared bymachining with a coarse-toothcutter or if this is not available,manually using a coarse file. Avoidgrinding with corundum or resinwheels.
Workpiece configuration is alsoimportant; this relates to: the clearance between theworkpieces – this must be assmall as possible (23) to preventdistortion, the size and shape of the bac-king bar (stainless steel).
Tables 49 and 50 illustrate anumber of examples of edgepreparation and configurationfound in shipbuilding.
8.FILLER METAL
The filler metal must becompatible with the chemicalcomposition of the parent alloysthat are to be welded, and mustensure the best possibleweldability.
The choice will also depend onthe mechanical properties andcorrosion resistance that the jointis required to have.
For the aluminium alloys that areused in shipbuilding (and othermarine applications), the fillermetals are: silicon alloys, mainly 4043A,4045, 4047A, magnesium alloys, mainly 5356,5183, 5556A.Their compositions are shown intable 51, p. 100.
Table 52, p. 101 - taken from EN1011–4 (24) - shows possiblechoices of filler metal according tothe hierarchy of criteria used forthe weld. 5183 is the best fillermetal for welding Sealium®.
98
(21) Chemical pickling in alkaline bathsshould be avoided at all cost. Thoroughwashing is essential and experienceshows that this is often inadequate, witha risk of subsequent corrosion by tracesof the alkaline medium.
(22) BS 8118 “Structural use ofaluminium, Part 2 Specification formaterials, workmanship and protection”states that the time between cleaningand welding must not exceed 6 hours.
(23) Zero clearance is the ideal.
(24) Standard EN 1011-4. Welding –Recommendations for welding ofmetallic materials. Part 4: Arc welding ofaluminium and aluminium alloys.
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6. WELDING
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EXAMPLES OF EDGE PREPARATION FOR BUTT WELDING MIG WELDING
α = 70/90° for flatand overheadweldsα = 70° for verticalwelds
t > 10none2 sidesalternately
Flat, vertical,overhead
Material over 12 mmthick should be weldedautomatically with ahigh current (+).Improvement andvisibility of the weld
8 < t < 30none 2 sidesalternately
Flat
Max. gap 2 mmtemporary
Max. gap 1.5 mm Back-weld advisablefor h = 3 mm (*)
3 < t < 25none1 side only Flat,vertical,overhead
t1 = t + 1 mm with max. 6 mm
permanent
Max. gap 3 mmtemporary
Max. gap 1.5 mm Back-weld advisablefor t > 4 mm (*)
3 < t ≤ 6none1 side onlyAll
RemarksPreparationThickness(mm)
BackingWeldingPosition
(*) Where a back-weld is advisable, it must be welded after gouging to the base of the first pass. Table 49
(*) Taken from standard NF 87-010 "Aluminium et alliages d'aluminium – Soudage – Préparation des bords" (Aluminium and aluminium alloys – Welding – Edge preparation).
t
t 1
t
Weld or track
Gaph h 1
t
70°
Gap
0,5
mm
For visibility if required
0,5
mm
70°
Gap
h
t
t
(Broken corners)(+)
1mm
1mm
α
t
1,5
to3
mm
t
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9.FINISHING
The purpose of weld finishingoperations is to: repair defective weldments, remove any black deposits leftby welding, correct structures with exces-sive distortion,
shave the seam, put the seam in compression byshot-peening, complete the concavity of theseam.
100
EXAMPLES OF EDGE PREPARATION FOR FILLET WELDS MIG WELDING (WELDS IN ALL POSITIONS, NO BACKING)
α = 70 °. Back-weld if possiblet > 61 side
If possible 1 back pass on otherside, 5 mm groove (*)
t > 41 side
t > 42 sides alternatelyor simultaneously,automatic flatwelding
RemarksPreparationThickness
(mm)Welding
(*) Where a back-weld is advisable, it must be welded after gouging to the base of the first pass. Table 50
(*) Taken from standard NF 87-010 "Aluminium et alliages d'aluminium – Soudage – Préparation des bords" (Aluminium and aluminium alloys – Welding – Edge preparation).
2m
m
M
ax.g
ap t
1,5
mm
Max
.gap
3mmt
60°
t
ht
h=t/4 to t/3
α
CHEMICAL COMPOSITION OF FILLER METALS (*)
Alloy Si Fe Cu Mn Mg Cr Zn Ti
4043A 4,5 0,6 0,30 0,15 0,20 0,10 0,156,0
4045 9,0 0,5 0,30 0,03 0,05 0,10 0,2011,0
4047A 11,0 0,6 0,30 0,15 0,10 0,20 0,1513,0
5356 0,25 0,40 0,10 0,05 4,5 0,05 0,10 0,060,20 5,5 0,20 0,20
5183 0,40 0,40 0,10 0,50 4,3 0,05 0,25 0,151,0 5,2 0,25
5556A 0,25 0,40 0,10 0,6 5,0 0,05 0,20 0,051,0 5,5 0,20 0,20
5556 (**) 0,25 0,40 0,10 0,50 4,7 0,05 0,25 0,051,0 5,5 0,20 0,20
(*) According to standard EN 573-3, Part 3: Aluminium and aluminium alloys – Chemical composition, except for the 5556. Table 51
(**) According to the Aluminum Association.
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9.1Repair of defective welds
If inspection (X-ray, ultrasonic etc.)reveals unacceptable weldimperfections then the weld mustbe repaired.
On material under 4 mm thick,defective areas can be removedwith a rotary tungsten carbidecutter mounted in a pneumatic
drill. The axis of rotation of thecutter must be parallel to the axisof the weld so as to avoid incipientcracks.
For material over 4 mm thick, thedefective areas should beremoved with a pneumatichammer fitted with a gouge (25).
The weld is then repaired by thesame process (TIG or MIG) as wasused to make the initial joint.
Minor imperfections are nearlyalways repaired by TIG weldinghowever, thickness allowing.
6. WELDING
101
Each combination has three possible choices - indicated where the lines intersect - depending on the selected criterion: Optimum mechanical properties: top line – Optimum resistance to corrosion: middle line – Optimum weldability:bottom lineThe filler metal indicated is: 4 : series 4xxx 4043A, 4045, 4047A – 5 : series 5xxx 5356, 5183, 5556A
Alloy A
Wrought 55000 Series 5 (a)Mg < 3% 4 - 5 (b)
Wrought 5 55000 Series 5 5Mg > 3% (a) 5 5
Wrought 5 - 4 5 - 4 5 - 46000 Series 5 5 5
4 4 4
Wrought 5 - 4 5 - 4 5 - 4 5 - 47000 Series 5 5 5
without copper 4 4 4
Cast 4 (e) 5 - 4 (e) 4 4 4 (d)Si > 7% 4 5 4 4
(c) 4 4 4 4
Wrought Wrought Wrought Wrought Cast Alloy B 5000 Series 5000 Series 6000 Series 7000 Series Si > 7%
Mg < 3% Mg > 3% without copper (c)
(a) 5000 series alloys with more than 3.5% Mg are sensitive to intergranular corrosion Table 52when exposed to temperatures over 65°C and when used in certain aggressive environments (26).
(b) 5000 series alloys with less than 3% Mg and 3000 series alloys that contain magnesium may be sensitive to hot cracking.
(c) The mechanical performance of the weld depends on the internal soundness of the castings. Gassed materials and injection mouldings are considered to be non-weldable.
(d) The percentage of silicon in the filler wire must be as near as possible to that in the casting.
(e) The welding of aluminium-silicon castings (40000 series) to 5000 series alloys should be avoided where possible as Mg2Si intermetallics form in the weldment and weaken the joint.
(25) Carbon arc gouging is not advisableas it may introduce carbon into the weldseam.
(26) Cf. Chapter 10, Section 10-2.
CHOICE OF FILLER METALS AS A FUNCTION OF THE ALLOY COMBINATION
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9.2Cleaning
Very fine black deposits of “soot”can often be seen sticking to thesurface of the metal at the edge ofthe weld seam after MIG welding,especially when 5000 seriessemis are welded with 5356 alloyas the filler metal.
4043A filler wire leaves nodeposits (except possibly at thestart and finish of the weld) pro-vided the welding equipment isset correctly.
This “soot” consists of particles ofoxides (of aluminium and magne-sium) caused by small amounts offiller metal vaporising in the arc,
the temperature of the arc beinghigher than the boiling point of alu-minium and magnesium. Thevapour immediately condenses oncold parts of the sheet near to theweld.
These deposits only affect theappearance of the weld and haveno impact on its mechanical prop-erties or corrosion resistance.
This “soot” can be brushed off witha metal brush. This should be doneas soon as possible after weldingas it becomes much more difficultto remove if left for several hours.
9.3Correcting distortion
Minor distortion in sheet under3 mm thick can be corrected witha hammer or mallet.
When sheets are bulged (figure84), the welding torch can beused to apply “shrinkage heat” aslocally as possible to the bulges.The heat makes these con-strained areas expand (thewelded zones are shorter thanthe sheet), and they are com-pressed. Rapid cooling – with ajet of water if necessary – thencauses shrinkage which placesthe piece under stress and so cor-rects the warp. “Shrinkage heat”may also be combined with ham-mering.
It is trickier to apply “shrinkageheat “ to aluminium than to steelbecause of the high diffusion ofheat. Unlike steel, aluminium doesnot change colour so the tempera-ture must be checked with tallowor thermocolour pencils.
Shrinkage heat does not affect themechanical properties of 5000alloys in the O or H111 condition.However it anneals 6000 seriesalloys and so reduces theirmechanical properties.
9.4Flush dressing of the weld
Flush dressing of the weld seamvery significantly improves thefatigue resistance of the joint pro-vided the seam is free from inter-nal flaws which flush dressingwould expose.
According to BS 8118 for example,shaving increases the endurancelimit of a seam from 24 MPa for a120° angle to 50 MPa for a dressedflush seam (27).
Welds are normally dressed flushwith a fine abrasive wheel (50 to80 grit).
9.5Shot-peening
Shot-peening a weld seam puts itssurface in compression, neutralis-ing internal stresses detrimentalto the weldment’s fatiguestrength.
Different types of shot can beused – glass, ceramic or steel –but it is the latter two which signif-icantly enhance fatigue strength(figure 85).
Although there is no way of verify-ing the efficiency of these treat-ments, they can be applied to thewelds of “hot spots”.
102102
DISTORTION OF PARTS IN COMPRESSION
Dishing
EFFECT OF PRE-STRESS SHOT-PEENING
As welded
Glass shot
Ceramic shot
Steel shot
Failure Failure No failure
No failure
107
106
105
104
103
Fatig
ue s
tren
gth
at 9
0 M
Pa, R
= 0
,1
5086 H111, 6 mm MIG butt welds
Figure 85
Figure 84
(27) Cf. figure 45, p. 65.
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6. WELDING
103
10.INSPECTION
The purpose of inspection is toevaluate the quality of fabricatedproducts and more specifically tograde the quality of a weld againstan acceptable level of defects.
The acceptable level of defects isdetermined by a number ofparameters:
the load modes and load condi-tions – static and dynamic, the levels and variations ofstress, the safety of persons and pro-perty, the technical and financialconsequences of failure, the options for routine operatio-nal inspection and control.
10.1Approval procedures
Approval procedures are contrac-tual but they also make referenceto standards (if any) and to the reg-ulations of classification societies,especially as regards the qualifica-tion of welders.
They may be complemented bythe fabricator’s own inhouse pro-cedures, governing welding meth-ods in particular.
Tensile and bending tests are con-ducted on test specimens follow-ing approval procedures laid downby the classification societies.These tests are very important asthey can help: to detect a lack of fusion that ishard to identify by NDT testing,and to adjust parameters so as tolimit defects.
10.2Testing welded joints
The frequency and extent of weldtesting will depend on a number ofcriteria, such as: structure, rate of stress, any loads imposed on thewelds.
In the course of fabrication it ispossible to perform: non-destructive tests includingrandom X-ray testing (28), ultraso-nic etc., visual inspection and dye-pene-tration (29) which can be perfor-med over the whole of somewelds to detect incipient cracks, tests of mechanical propertiesand bending tests on specimenstaken from batches of weldedmetal according to the currentmethods
11.WELD IMPERFECTIONS
The causes of weld imperfectionsare numerous, and are a result ofeither the preparation of the metalor poor workmanship.
The most common defects en-countered in aluminium weldingare virtually the same as are foundin the welding of steel: isolatedcracks (‘star cracks’) or longitudinalcracks, incomplete penetration,poor bonding (fusion), porosity andundercuts.
Standards define weld imperfec-tions based on measurements ona cross section (figure 86) of theweld and observations on itsappearance.
An international nomenclature ofdefects has been established andis given in EN ISO 6520-1 (30)which lists 6 groups of imperfec-tions, as shown in table 53, p. 104).
GEOMETRICAL CHECKING OF WELDS
Butt welds
d
θ
s
rry
sry
θ
a
T Joint or Fillet welds
Misalignment: dToe angles at base of bead: θToe radii at base of weld: ry
Toe angles at base of bead: θToe radii at base of weld: ry
All numerical values are expressed in degrees or mm
Figure 86
(28) X-ray testing is not normallypossible on fillet welds.
(29) According to NF A 09-120. Non-destructive tests. General principles ofdye-penetration testing. June 1984.
(30) EN ISO 6520-1 Classification ofgeometric imperfections in metallicmaterials. Part 1: Fusion welding.
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11.1Common weld imperfections
Table 54 lists the most commonimperfections together with theirlikely causes.
104
GROUPS OF WELD IMPERFECTIONSGroup Type of Imperfection
100 Cracks
200 Cavities and wormholes
300 Solid inclusions
400 Lack of fusion and penetration
500 Defects of shape
600 Sundry defects
Table 53
N° Type of Defect Likely Cause Photos of Imperfections
101 Cracks Base alloy unsuitablePoor choice of filler metalIncorrect welding sequenceExcessive clampingSudden cooling
104 Crater cracks Pass finished with sudden arc cutoff
2012 Irregular wormholes Work inadequately degreasedWork and/or filler wire dirty or wetInsufficient protection by inert gas (low gas flow or leak in the system)Pass begun on cold componentHigh arc voltageWeld cooled too quickly
2014 Aligned wormholes Incomplete penetration (double pass)Temperature gradient between backing and work too abruptExcessive gap between edges of the joint
300 Solid inclusions Dirty metal (oxides, brush hairs)
303 Oxide inclusions Poor gas shieldingMetal stored in poor conditionsCastings
3041 Tungsten inclusions Electrode diameter too small(TIG) Poor handling by welder
Excessive current densityPoor quality of tungsten electrode
402 Incomplete penetration Inadequate cleaning (presence of oxide)Incorrect bevel preparation on thick work (too tight, excessive shoulder)Gap between workpieces too small (or incon-sistent) Low current, especially at the start of the seamWelding speed too fastHigh arc voltage
TYPICAL WELD IMPERFECTIONS
Defect 101
Defect 104
Defect 2012
Defect 300
Defect 402
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11.2Effect of weld imperfections on fatigue strength
Some weld defects have a signifi-cant impact on the fatiguestrength of the weldment:
cracks (emergent or otherwise)and incomplete penetration arevery serious flaws, as shown bytests carried out on welddefects [5] (figure 87), defects of geometry, especiallysudden breaks in curves (angle at
the base of the weld seam, mis-alignment etc.) aggravate stressintensity factors.
6. WELDING
N° Type of Defect Likely Cause Photos of Imperfections
4011 Lack of fusion High arc voltageon edges Low current, especially at the start
of the seamWork cold (difference in thickness between materials to be welded)
502 Excessive thickness Poor power control (poor U/I match)Welding speed too slow Poor edge preparation on thick workInsufficient starting current
507 Misalignment Work positioned incorrectlyIncorrect welding sequence
508 Angle defect Excessive welding powerIncorrect welding sequence
509 Collapse Wire speed too fastTorch speed too slowPoor torch guidance
602 Splatter (or beads) Incorrect arc controlProblem in electrical contact to ground
BUTT WELD IMPERFECTIONS
MisalignmentBlistersExcessive thicknessSide undercutsLack of penetration, exposedV-groove weld, no imperfection (reference)Double V-groove weld no imperfection (référence)Lack of penetration, exposed
5083 O
∆σ = 90 MPa
MisalignmentBlistersExcessive thicknessSide undercutsLack of penetration, exposedV-groove weld, no imperfection (reference)Double V-groove weld no imperfection (référence)Lack of penetration, exposed
6061 T6
∆σ = 99 MPa
103 104 105 106 107 Nb of cycles
Endurance limit (R = 0,1)
Figure 87
Table 54
Defect 402
Defect 502
Defect 507
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12.REPAIRS AND FITTINGS
European shipyards have respondedto needs for the maintenance andmodification of aluminium highspeed ships by adapting to and spe-cialising in this new activity [6, 7, 8].
These yards repair damage toships and modify onboard installa-tions. The very long service life ofaluminium ships means that fromtime to time they must be adaptedin line with changing conditions ofservice, new equipment must beinstalled etc.
Work on aluminium alloy struc-tures is based on classical sheetmetalworking operations as iscommonly carried out on steelships (and their equipment), e.g.sheet and plate cutting, preparingedges for welding, making welds,correcting distortion etc.
The rules discussed previously foraluminium alloy forming and weld-ing apply equally to these opera-tions.
A number of basic precautionsshould be taken when weldingitems that are being repaired ormodified: clean surfaces near to the weldwith great care, using a brush toremove all traces of paint, oil or fuelthat could have fouled the plates, dry thoroughly before weldingto remove all traces of moisture, weld under cover of weatherand away from draughts; if neces-sary, work under a tarpaulin whenthese operations are carried outin dock, pay particular attention to thedirection in which welds are made– this will limit distortion and mini-mise the risks of hot cracking dueto shrinkage, select the correct welding pro-cess: TIG (for work less than 6 mm
thick) or MIG. TIG is more suitablefor minor repairs where backaccess is difficult or impossible,being easier to use in such situa-tions and providing better controlof penetration than MIG.
For localised repairs such as a tornhull, the repair patch must be per-fectly matched to the shape of thetear but will be bigger (achieved byhammering) to compensate forthe contraction caused by weld-ing. Without this precaution, theresidual stress would attain a levelwhere it would cause systematiccracking. The smaller the patch,the more pronounced this phe-nomenon.
Important note: Never work with a torch or electricarc on or in any enclosed space,tank etc. that has held water(including seawater) or which hasbeen in contact with moisturewithout first airing or thoroughlyventilating it to disperse the hydro-gen produced by possible corro-sion of the metal in contact withwater. Failure to take this precau-tion may lead to an explosion haz-ard with consequences that couldprove catastrophic for the opera-tors (31). It is also a mandatoryprecaution for any work on fuel oiltanks.
13.LASER WELDING
Since the early Nineties, the usesof welding by laser (32) havespread widely in shipbuilding [9].
13.1Principle of the laser
The laser is a device that gener-ates an intense beam of coherentmonochromatic radiation. In weld-ing machines, this radiation is con-centrated to obtain power densi-ties in excess of 106 W.cm-2 whichis sufficient for the industrial weld-ing of aluminium alloys.
This power is used to generate acapillary filled with metallic vapourwhose walls are lined with liquidmetal in fusion. The resulting weldpool bath is displaced and the liq-uid metal solidifies after the beamhas passed, ensuring metallurgicalcontinuity between the work-pieces (figure 88).
13.2Welding lasers
Two types of industrial laser areused for welding metals:
in CO2
lasers the activemedium is a gaseous blend of car-bon dioxide (CO2), nitrogen (N2)and helium (H2) at low pressure.The wavelength of the laser beamis 10.6 µm. Industrial CO2 laserscan generate power ranging from1.5 to 40 kW. The beam is trans-mitted by mirrors.
(31) The amount of hydrogen that buildsup in a ballast tank can be considerableeven though corrosion is only superficial.In a tank with sides 1 metre long forexample, i.e. 5 m2 of area in contactwith water, superficial corrosion onemicron deep releases 16.8 litres ofhydrogen !!!
(32) Light Amplification by StimulatedEmission of Radiation.
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in Nd:YAG lasers (NeodymeYttrium Garnet), the activemedium is a solid and the radiationwavelength is 1.06 µm, with amaximum available power of 3 to4 kW. Despite their low power,Nd:YAG lasers offer a number ofadvantages over CO2 lasers: thesources are more compact, andNd:YAG beams can be carried byfibre optics which makes it possi-ble to weld along complex pathsusing welding robots.
13.3Laser welding of aluminium alloys
Aluminium alloys can be laserwelded with no particular difficultyand at speeds as high as severalmetres per minute.
Laser welding offers a number ofadvantages: simplicity of preparation beforewelding, high welding speeds, severalmetres/minute on butt welds in 6mm plate made from 5000 alloy, reduced distortion owing to thehigh welding speed and narrow-ness of the weldment, high penetration by the beam; itis possible to weld (CO2 laser)5000 series plate up to 12 mmthick in a single pass, high mechanical properties ofthe weld: nearly 90% of the parentmetal on 5083 H116 and 70% for6082 T6, different thicknesses can bewelded, ‘invisible’ welding, good final condition (minimalfinishing required), advanced automation.
Nevertheless laser welding requiresclose preparation tolerances andits energy efficiency is low.
13.4Laser weldability of aluminium alloys
Aluminium alloys have a relativelylow light absorption rate in the far-infrared: 3% with the CO2 laserand 25% with the Nd:YAG laser.However this coefficient of absorp-tion rises rapidly above fusion tem-perature and is approximately 90%when the material’s vaporisationtemperature is reached (figure 89).
For welding therefore, vaporisa-tion of the metal must be initiatedin the laser beam. Two very differ-ent types of interaction areobserved according to the powerdensity at the surface of the mate-rial (figure 90):
6. WELDING
LASER WELDING
HAZ
Laser beam
Capillary
HAZ
Resolidifiedmoltenmetal
Laser beam
Upstream weldpool
Capillary full offmetallic vapour
Weld
ing
dire
ctio
n
Figure 88
COEFFICIENT OF REFLECTIONOF LASER BEAMS
100
80
60
40
20
0Tf Tv T
Coe
ffic
ient
of
refle
ctio
n of
lase
r be
ams
λ = 10,6 µ (CO2)
λ = 1,06 µ(Nd: YAG)
%
Tf: fusion temperatureTv: Vaporisation temperature
Figure 89
INTERACTION BETWEEN LASER BEAM AND ALUMINIUM
Fusion zone Fusion zone Fusion zone
Plasma Absorbent plasma
Beam Beam Beam
p < 106 W/cm2
Surface fusion over some tens
of microns
106 < p < 107 W/cm2
Formation of« Keyhole » (optimum)
p > 107 W/cm2
Screen effect
Figure 90
Downstream weld pool
Welding dire
ction
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at low densities, fusion is verysuperficial, at high densities a vapourcapillary forms, i.e. a narrow anddeep zone of fusion in the metal. Itis this interaction which is neededfor welding.
The threshold of interaction, i.e.the power density needed to forma vapour capillary, is of the order of106 W.cm-2. The value of thisthreshold depends on the compo-sition of the alloy – alloys that con-tain magnesium in the 5000 series(5754, 5083, 5086, etc.) have alower threshold of interaction thanother alloys (figure 91) and can bewelded with less power.
It is important to note that usingtoo high a power density iscounter-productive as the metalvapours will form a plasma thatacts as a shield. This is particularlytrue of CO2 lasers.
A shielding gas must be used toprevent the immediate oxidationof the weld pool, and with CO2
lasers the best results areobtained with argon/helium blendsor pure helium. Argon can also beused with Nd:YAG lasers.
14.FRICTION STIR WELDING (FSW)
Friction welding with a tool (33)was invented by the TWI (34), thefirst patent being filed inDecember 1991 [10].
It is clear that this has been a deci-sive advance in the joining of met-als in general and aluminium alloysin particular. In under ten yearsthis new welding technique hasenjoyed significant industrialdevelopment and growth in anumber of sectors including ship-building, aerospace and the rail-ways [11].
Since 1995 many publicationshave appeared and presentationsgiven on the applications of FSWwelding in shipbuilding at interna-tional conferences on High SpeedShips made from aluminium [12].These publications reflect theobvious interest shown by navalarchitects and yards in this newtechnique, one which is alreadymaking very significant changes toaluminium shipbuilding and givingit fresh impetus [13, 14].
14.1Principle of frictionstir welding
The process is a simple one, con-sisting of shearing the metalwithout melting it (it turns ‘pasty’)with a rotating tool that has a‘probe’ or pin on a level slightlybelow that of the weld. As itrotates the tool stirs the metal ofthe workpieces together and dis-charges it to the rear where theweld thus formed is softened andconsolidated.
The metal is made to flow by theheat from the friction of the rotat-ing shoulder against the surface ofthe metal. The shoulder, which islarger in diameter than the probe,contains the moving particles ofmetal and maintains a pressurethat prevents the metal frombeing ejected outside the weldedzone (figure 92).
The very significant forces that areexerted on the work mean that itmust be clamped very firmly tothe table of the welding machine.
14.2Microstructure of the FSW joint
The specific properties of the FSWjoint are due to its microstructurewhich is very different from themicrostructure of an arc weld(MIG or TIG) owing to the simplefact that there is no process offusion / solidification. An FSW weld has four very dis-tinct zones (figure 93) [15]:
zone A, outside the weld, is theparent metal of each of the work-pieces on either side of the joint.Its structure is unaffected by wel-ding, zone B is the heat affectedzone. It does not undergo anyplastic deformation. As with theHAZ of conventional MIG or TIGwelds, its mechanical properties
THRESHOLD OF LASER INTERACTION
Pene
trat
ion
dep
th
mm
2
1
0
Specific power in focal plane lm
1 2 3 4 5
106W/cm2
Welding speed Vs = 6 m/minFocusing plane ∆z = + 0,5 mmFocal length f = 150 mmConvergence factor F = 5,0Radius of final point rf = 136 µm
–– 5182 –– 5754 –– 6082
Figure 91
(33) Friction stir welding (FSW).
(34) TWI: The Welding Institute.
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are low (figure 94). This zone isannealed in strain hardened alloysand over-aged in age hardenedalloys (35). However no deforma-tion occurs because the heatingup of the metal and the tempera-ture level attained are much lowerthan in arc welding, zone C is the thermomechani-cally affected zone that has under-gone plastic deformation and hea-ting. The structure of this zonedepends on a number of parame-ters including the type of alloy, zone D is the “nugget” formedfrom recrystallised grains in whichthe metallurgical constituents ofthe parent alloys are dispersed.The grains are usually smaller thanin the parent metal. This structureenhances the fatigue resistance ofthe welded joint.
In age hardened alloys the nuggetis in a condition close to T4 (solu-tion heat treated, natural ageing atambient temperature) (figure 95).
14.3Comparisons with arc welding
The FSW process operates at atemperature below the meltingpoint of the metal, offering a num-ber of advantages:
conditions of use are simpli-fied: surface preparation is confi-ned to degreasing only. Whereedge preparation is necessary,surfacing is adequate. The processrequires no filler metal or shieldinggas, the applications of FSW are farmore extensive than with arc wel-ding: all types of aluminium alloyproducts can be welded, whethercastings or wrought semis, the quality of the weld: thereare no risks of hot cracking (36) orporosity as hydrogen is not for-med (37), the quality of the assemblies:
distortion is minimal owing to thelow temperature levels and thefact that welding takes place in asolid medium,
6. WELDING
FRICTION WELDING TOOLS
Downward force
Tooladvance
Probe
Trailing edge of tool
Shoulder
Weld
Figure 92
MICROSTRUCTURE OF THE FSW JOINT
A: Parent metal unaffected by weldB: Heat affected zone (HAZ)C: Unrecrystallised area found in aluminium alloysD: Recrystallised nugget found in aluminium alloys
Width of tool shoulder
CC D
BA B A
CHANGE IN HARDNESS IN THE HAZ OF 5083 [15]
100
90
80
70
60-40 -30 -20 -10 0 10 20 30 40
Har
dnes
sH
b
Distance from weld centre (mm)
5083 O5083 H321
CHANGE IN HARDNESS IN THE HAZ [16]
120
100
80
60
40
20
00 10 20 30 40
Centre of weld
6082 T6As weldedaged 3 h at 185°C
Har
dnes
sH
b
Distance across weld (mm)
120
100
80
60
40
20
00 10 20 30 40
Centre of weld
6082 T4As weldedAged 3 h at 185°C
Har
dnes
sH
b
Distance across weld (mm)
Figure 93
Figure 94
Figure 95
(35) As a result the alloys are in themetallurgical condition indicatedpreviously.
(36) It is possible to weld copper alloys(2000 and 7000 series).
(37) If hydrogen did form it would not bedissolved because its solubility in solidaluminium is zero.
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environmental and working
conditions: there are no fumes,no flying particles of metal, noozone emissions and no ultravioletradiation. The process is alsoenergy efficient, requiring about20% of the power of MIG welding.
Its present state of industrialdevelopment makes FSW highlysuitable for prefabricating sub-assemblies such as deck sections,walls, panels etc. [17] in the work-shop for subsequent installation inships and assembly by conven-tional welding techniques such asMIG (38).
A prototype “portable” machinedesigned by the University ofAdelaide in Australia with TheWelding Institute was presentedrecently [18]. This is in fact a toolconnected to a hydraulic motorand mounted on a trolley for weld-ing hull plates 5 mm thick.However although the tool is“portable”, the components to bebutt welded must be firmly fixedto withstand the forces necessaryfor welding.
14.4Possibilities of welding with FSW
In its present state of advance,FSW allows the welding of mate-rial up to 25 mm thick. Researchinto 6000 series alloys has shownthat it is possible to go up to 50mm thick with a single head (fig-ure 96), and 75 mm with twoheads (figure 97).
Given the current level of industrialdevelopment of the process, FSWcan be envisaged in a number ofconfigurations for butt welds and‘invisible’ welds as shown infigure 98.
(38) A welding code is in the process ofbeing approved by the classificationsocieties.
WHORLTM TOOL
75 mm section of 6082
FSW WELDING WITH TWO HEADS
Adjustable roller guides Contra rotating tools
TYPICAL FSW WELD CONFIGURATIONS
a b c
d ef
a: Butt weld
b: Invisible weld
c: Invisible weld in several thicknesses
d: Welding brackets in Tee
e: Invisible Tee weld
f: Fillet weld inside
Figure 97
Figure 96
Figure 98
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14.5Performance of FSW welds
There have been numerous stud-ies characterising the properties ofFSW welds – their mechanicalproperties, fatigue strength andcorrosion resistance of the weld-ment [19].
Mechanical properties
The mechanical properties of FSWwelded metal are superior to thoseof MIG welded metal (table 55).
Fractures usually occur at theedge of the friction zone, neverinside it, most probably becauseof the strain hardening caused bythe base of the tool.
The limit of elasticity is at least10% higher in FSW welded metalthan MIG welded.
Fatigue resistance
The limit of endurance of FSWwelded metal is superior to that of aMIG weld [21] (figure 99 and table 56).
The limit of endurance of an FSWweld is always superior to that of aMIG welded joint, and this is true
for all alloys. This is because FSWensures a very good connectionbetween the joined workpieces.There is no ‘sticking’ (i.e. lack offusion). It goes without saying thatthis applies only when the FSWjoint is free from imperfections.
Corrosion resistance
Investigations carried out so farhave not indicated any particularsensitivity to corrosion by FSWwelds. Their resistance to corro-sion is at least equal to that of MIGor TIG welds.
6. WELDING
Alloy Welding Rp0,2 (MPa) Rm (MPa) A %
5083 H116 MIG 134 287 12,8 FSW 157 335 17
Sealium® MIG 150 308 13,5 FSW 165 354 17
MECHANICAL PROPERTIES OF WELDED 5083 AND 5383 6 MM THICK [20]
Table 55
LIMIT OF ENDURANCE ON 5383 (AT 107 CYCLES FOR R = 0.1) [11]
Alloy Welding Limit of Endurance (MPa)
Sealium® Parent metal 228 FSW 172 MIG 144
Table 56
MPa
N
400
100
50
20104 105 106 107 3.107
5083 plate5083 welded
Recommendations ECCS,class B3
Str
ess
rang
e
LIMIT OF ENDURANCE OF FSW JOINTS
Figure 99
ENGINE AND DRIVE SHAFT BEARER
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15.STANDARDS
The main standards that governthe welding of aluminium arelisted in table 57..
Reference Date Subject
BS EN 1011-4 Dec 2000 Welding. Recommendations for welding of metallic materials.
Part 4: Arc welding of aluminium and aluminium alloys.
NF A 89-310 April 1973 Aluminium et alliages d'aluminium - Soudage - Assemblages
élémentaires types - Critères de choix.
NF A 87-010 April 1973 Aluminium et alliages d'aluminium - Soudage - Préparation des bords.
BS EN 288-4/A1 August 1997 Specification and approval of welding procedures for metallic materials.
Welding procedure tests for the arc welding of aluminium and its alloys.
NF A 89-220 April 1973 Aluminium et alliages d'aluminium - Soudage - Classification et contrôle
des joints soudés.
BS 8118 Structural use of aluminium. Part 2. Specifications for materials,
workmanship and protection.
BS EN ISO 9692-3 Dec 2001 Welding and allied processes. Recommendations for joint preparation.
Part 3: Metal inert gas welding and tungsten inert gas welding of
aluminium and its alloys. (ISO 9692-3:2000).
BS EN 12584 June 1999 Imperfections in oxyfuel flame cuts, laser beam cuts and plasma cuts.
Terminology.
BS EN 30042 July 1994 Arc-welded joints in aluminium and its weldable alloys. Guidance on
ISO 10042 quality levels for imperfections.
BS EN ISO 13919-2 Dec 2001 Welding -- Electron and laser beam welded joints -- Guidance on quality
levels for imperfections -- Part 2: Aluminium and its weldable alloys
(ISO 13919-2:2001).
BS EN ISO 6520-1 Dec 1998 Welding and allied processes -- Classification of geometric imperfections
in metallic materials -- Part 1: Fusion welding (ISO 6520-1:1998).
NF EN 83-100-1 Dec 1995 Construction d'ensembles mécano soudés. Techniques de soudage.
Partie 1 – Généralités: Terminologie, Classes de qualité de soudure –
Etendue des contrôles.
BS EN 12062 1998 Non-destructive examination of welds. General rules for metallic
materials.
BS EN 970 May 1997 Non-destructive examination of fusion welds. Visual examination.
NF A 09-120 June 1984 Essais non destructifs. Principe généraux de l'examen par ressuage.
MAIN EUROPEAN STANDARDS FOR WELDING OF ALUMINIUM
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Bibliography[1] “Soudure et chaudronneried’aluminium”, Revue de l’aluminium,No. 99, March 1938, pp. 1128-1135.
[2] “Le soudage à l’arc des métauxlégers avec électrode fusible enrobée”,CHARLES GUINARD, Revue de l’aluminium,No. 167, June 1950, pp. 237-244.
[3] “Die Fügetechniken des Aluminiumsim Laufe der Jahrzehnte“, G. AICHELE,Aluminium, Vol. 75, pp. 743-753, 1999.
[4] “Construction of the All-Welded Twin-Screw Auxilliary Motor Yacht”, J. G.YOUNG, British Welding Journal, January1955, pp. 1-18.
[5] “Nocivité des de soudage suréprouvettes soudées MIG” D. ALBERT, C.HANTRAIS, M. MÉDIOUNI, M. TRICOT,Rapport Pechiney CRV 3535, December1994.
[6] “Repair yards show their versatility”,Speed at Sea, April 1998.
[7] “Routine repairs provide annualreturns”, Speed at Sea, January 1999.
[8] “Aluminium skills are part of routineworkload”, Speed at Sea, October 2000.
[9] “Developments in welding techniquesfor aluminium alloys”, J. D. RUSSEL, C. J.DAWES, R. L. JONES, TWI, ConferenceSouthampton 1996.
[10] “Improvements relating to frictionwelding”, W M THOMAS, E D NICHOLAS, JC NEEDHAM, MG MURCH, P TEMPLE SMITH,CJ DAWES, (TWI), Patent GB 91 25978.8,International PCT/GB92/02203 andEuropean Patent Specification 0 615 480B1.
[11] “Application of Friction Stir Weldingfor manufacture of aluminium ferries”, S.W. KALLE, E. D. NICHOLAS, P. M. BURLING,TWI, 4th International Forum onAluminium Ships, New Orleans, May2000.
6. WELDING
Reference Date Subject
BS EN 1289 August 1998 Non-destructive examination of welds. Penetrant testing of welds.
Acceptance levels.
BS EN 1712 Nov 1997 Non-destructive examination of welds. Ultrasonic examination of welded
joints. Acceptance levels.
BS EN 1713 Sept 1998 Non-destructive examination of welds. Ultrasonic examination.
Characterization of indications in welds.
BS EN 1714 Oct 1997 Non-destructive examination of welded joints. Ultrasonic examination of
welded joints.
BS EN 1712/A1 February2003 Non-destructive examination of welds. Ultrasonic examination of welded
joints. Acceptance levels.
BS EN 1714/A1 February 2003 Non-destructive examination of welded joints. Ultrasonic examination of
welded joints.
BS EN 444 April 1994 Non-destructive testing. General principles for radiographic examination
of metallic materials by X- and gamma-rays.
BS EN 1435 Oct 1997 Non-destructive examination of welds. Radiographic examination of
welded joints.
BS EN 12517 Sept 1998 Non-destructive examination of welds. Radiographic examination of
welded joints. Acceptance levels.
BS EN 287-2 June 1992 Approval testing of welders for fusion welding. Aluminium and
aluminium alloys.
BS EN 287-2/A1 August 1997 Approval testing of welders for fusion welding. Aluminium and
aluminium alloys.
BS EN ISO 9956-10 Nov 1996 Specification and approval of welding procedures for metallic materials --
Part 10: Welding procedure specification for electron beam welding.
BS EN ISO 9956-11 Nov 1996 Specification and approval of welding procedures for metallic materials --
Part 11: Welding procedure specification for laser beam welding.
BS EN 12345 June 1999 Welding. Multilingual terms for welded joints with illustrations.
BS EN 1792 2003 Welding. Multilingual list of terms for welding and related processes.
Table 57
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[12] “4th International Forum onAluminium Ships”, New Orleans, May2000
“European Shipbuilding in the 21thCentury”, London, December 2000.
“The Third International Forum onAluminium Ships”, Haugesund, May1998.
“Lightweight Construction – LatestDevelopments”, The Royal Institution ofNaval Architects, London February 2000.
[13] “Studies extend Friction Stir Weldingpotential”, Speed at Sea, October 1998,p. 45.
[14] “Friction Stir benefits include costsaving”, P. HYNDS, Speed at Sea, October1999, p. 33.
[15] “Friction Stir Welding in aluminiumalloys, preliminary microstructuralassessment”, P L THREADGILL, TWIBulletin, Vol. 28 (2), March 1997,pp. 30–33 .
[16] “Friction Stir Welding – Weldproperties and manufacturingtechniques”, Proc INALCO-7, CambridgeApril 1998, pp. 171–181.
[17] “Application of prefabricated FrictionStir Welding panels in catamaranbuilding”, O. T. MIDLING, J. S. KVÄLE, S.OMA, 4th International Forum onAluminium Ships, New Orleans, May2000.
[18] “Exploiting friction stir welding inexplosevely-formed aluminium boat hullconstruction”, I. HENDERSON, Joints inaluminium, INALCO 98, 1998, pp. 261-267.
[19] “Friction Stir Welding – The state ofthe art”, P. L. THREADGILL; Report TWI7417.01/99/1012
[20] Pechiney Report CRV February 1999.
[21] “Friction Stir Welding aluminiumalloy 5083, Increased welding speed”, C.J. DAWES, E. J. R. SPURGIN, D. G. STAINES,Report TWI 7735.1/98/993.2.
MARINA AT TRINITÉ-SUR-MER
