Effect+of+pulsed+current+tig+welding+parameters+on+pitting+corrosion+behaviour+of+aa6061+aluminium+alloy (1)

J. Mater. Sci. Technol., Vol.23 No.2, 2007 223

Effect of Pulsed Current TIG Welding Parameters on Pitting

Corrosion Behaviour of AA6061 Aluminium Alloy

T.Senthil Kumar1), V.Balasubramanian2)†, M.Y.Sanavullah3) and S.Babu2)

1) Department of Automobile Technology, Bharathidasan University, Tiruchirappalli 620 024, India2) Department of Manufacturing Engineering, Annamalai University, Annamalainagar 608 002, India

3) Principal, V.M.K.V.Engineering College, Salem 636 308, India

[Manuscript received September 29, 2005, in revised form June 23, 2006]

Medium strength aluminium alloy (Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of lightweight structures requiring a high strength-to weight ratio, such as transportable bridge girders, militaryvehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy isfrequently TIG (tungsten inert gas) welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been foundbeneficial due to its advantages over the conventional continuous current process. The use of pulsed currentparameters has been found to improve the mechanical properties of the welds compared to those of continuouscurrent welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model hasbeen developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variancetechnique has been used to find out the significant pulsed current parameters. Regression analysis has beenused to develop the model. Using the developed model pitting corrosion potential values have been estimatedfor different combinations of pulsed current parameters and the results are analyzed in detail.

KEY WORDS: Pulsed current; Tungsten inert gas welding; Medium strength aluminium alloy;

Pitting corrosion; Design of experiments; Analysis of variance

1. Introduction

Weld fusion zones typically exhibit coarse colum-nar grains because of the prevailing thermal condi-tions during weld metal solidification. This often re-sults in inferior weld mechanical properties and poorresistance to hot cracking. It is thus highly desirableto control solidification structure in welds and such acontrol is often very difficult because of higher tem-peratures and higher thermal gradients in welds inrelation to castings and the epitaxial nature of thegrowth process. Nevertheless, several methods for re-fining weld fusion zones have been tried with somesuccess in the past: inoculation with heterogeneousnucleants[1], microcooler additions, surface nucleationinduced by gas impingement and introduction of phys-ical disturbance through torch vibration[2].

The use of inoculants for refining the weld fusionzones is, as a matter of fact, not as successful as incastings because of the extremely high temperatureinvolved in welding and also due to the undesirable ef-fect of inoculating elements on weld mechanical prop-erties at the level required for grain refinement. Othertechniques like surface nucleation and microcooler ad-ditions were also turned down because of the compli-cated welding set-ups and procedures associated withtheir use. In this process, two relatively new tech-niques, termed as magnetic arc oscillation and cur-rent pulsing, have gained wide popularity because oftheir striking promise and the relative ease with whichthese techniques can be applied to actual industrialsituations with only minor modifications of the exist-ing welding equipment[3].

† Prof., Ph.D.(IITM), to whom correspondence should beaddressed, E-mail: [email protected].

Pulsed current tungsten inert gas (PCTIG) weld-ing, developed in 1950s, is a variant of TIG weldingwhich involves cycling of the welding current from ahigh level to a low one at a selected regular frequency.The high level of the peak current is generally selectedto give adequate penetration and bead contour, whilethe low one of the background current is set at a levelsufficient to maintain a stable arc. This permits arcenergy to be used efficiently to fuse a spot of controlleddimensions in a short time producing the weld as a se-ries of overlapping nuggets and limits the wastage ofheat by conducting into the adjacent parent materialin a normal constant current welding. In contrast toconstant current welding, the fact that the heat en-ergy required to melt the base material is suppliedonly during peak current pulses for brief intervals oftime allows the heat to dissipate into the base mate-rial leading to a narrower heat affected zone (HAZ).The technique has secured a niche for itself in specificapplications such as in welding of root passes of tubes,and in welding thin sheets, where precise control overpenetration and heat input are required to avoid burnthrough.

Extensive researches have been performed in thisprocess and reported advantages include improvedbead contour, greater tolerance to heat sink varia-tions, lower heat input requirements, reduced residualstresses and distortion[4]. Metallurgical advantages ofpulsed current welding frequently reported in litera-ture include refinement of fusion zone grain size andsubstructure, reduced width of HAZ, control of seg-regation, etc.[5]. All these factors will help in improv-ing mechanical properties. Current pulsing has beenused by several investigators to obtain refined grainsin weld fusion zones and improvement in weld me-chanical properties[6,7]. However, reported research

224 J. Mater. Sci. Technol., Vol.23 No.2, 2007

Table 1 Important factors and their levels

Levels Peak current, P/A Base current, B/A Pulse frequency, F/Hz Pulse on time, T/%Low (−1) 160 80 2 40High (+1) 180 90 6 60

Table 2 Experimental design matrix and test results

Expt No. P B F T ∗PCP/mV1 −1 −1 −1 −1 −5002 +1 −1 −1 −1 −4753 −1 +1 −1 −1 −5904 +1 +1 −1 −1 −5405 −1 −1 +1 −1 −4956 +1 −1 +1 −1 −4607 −1 +1 +1 −1 −5358 +1 +1 +1 −1 −5109 −1 −1 −1 +1 −55010 +1 −1 −1 +1 −50511 −1 +1 −1 +1 −60012 +1 +1 −1 +1 −57513 −1 −1 +1 +1 −52514 +1 −1 +1 +1 −49015 −1 +1 +1 +1 −56016 +1 +1 +1 +1 −530

Note: ∗PCP—pitting corrosion potential

work on the effect of pulsed current parameters on me-chanical and metallurgical properties are very scant.Moreover, no systematic study has been reported toanalyze the influence of pulsed current parameters onmechanical and metallurgical properties.

Thus, in this investigation an attempt was madeto develop a mathematical model to predict the effectof pulsed current TIG welding parameters on pittingcorrosion behaviour of medium strength AA6061 alu-minium alloy using statistical tools such as design ofexperiments, analysis of variance and regression anal-ysis.

2. Scheme of Investigation

In order to achieve the desired aim, the present in-vestigation was planned in the following sequence: (1)identifying the important pulsed current TIG weldingparameters, which have influence on grain refinementin fusion zone and corrosion resistance; (2) finding theupper and lower limits of the identified parameters;(3) developing the experimental design matrix; (4)conducting the experiments according to the designmatrix; (5) recording the responses; (6) developingmathematical models; (7) identifying the significantfactors; (8) checking the adequacy of the developedmodels.

2.1 Identifying the important parametersFrom the literature[5–8] and our previous work[9],

the predominant factors which have greater influenceon fusion zone grain refinement of pulsed current TIGwelding process have been identified. They include:(1) peak current; (2) background current; (3) pulsefrequency and (4) pulse on time.

2.2 Finding the working limits of the parametersA large number of trial runs were carried out us-

ing 5 mm thick rolled plates of AA6061 aluminium

alloy to find out the feasible working limits of pulsedcurrent TIG welding parameters. AA4043 (Al-5%Si)aluminium alloy of 3 mm diameter was used as thefiller metal and different combinations of pulsed cur-rent parameters were used to carry out the trial runs.The bead contour, bead appearance and weld qualitywere inspected to identify the working limits of thewelding parameters. From the above analysis, thefollowing observations were made.

(1) When peak current was less than 160 A, incom-plete penetration and lack of fusion was observed. Atthe same time, when peak current was greater than180 A, undercut and spatter was observed on the weldbead surface.

(2) When background current is lower than 80 A,the arc length was found to be very short and addi-tion of filler metal became inconvenient. On the otherhand, when the background current was greater than90 A, the arc became unstable and arc wandering wasobserved due to its increased arc length.

(3) The bead appearance and contours appear tobe similar to that of constant current weld beads whenpulse frequency was less than 2 Hz, while more arcglare and spatter was experienced if pulse frequencywas greater than 6 Hz.

(4) When pulse on time was lower than 40%, theweld nugget formation was not so smooth due to in-complete melting of filler metal. On the contrary,when the pulse on time was greater than 60%, theovermelting of filler metal and overheating of tung-sten electrode was noticed.

2.3 Developing the experimental design matrixBy considering all the above conditions, the fea-

sible limits of the parameters have been chosen suchthat the AA6061 aluminium alloy should be weldedwithout any weld defects. Due to narrow ranges offactors, we decided to use two level, full factorial de-sign matrix to optimize the experimental conditions.Table 1 presents the ranges of factors considered andTable 2 shows the 16 sets of coded conditions used toform the design matrix, 24 (2 levels and 4 factors) fac-torial design. The 16 experimental conditions (rows)have been formed for main effects by using the for-mula 2nc−1 for the low (−1) and high (+1) values;where ‘nc’ refers to the column number. For exam-ple, in Table 2, the first four rows are coded as −1 andnext four rows are coded as +1, alternatively, in thethird column (because nc=3 and therefore 23−1=4).The method of designing such a matrix can be foundin literature[10,11].

For the convenience of recording and processingthe experimental data, upper and lower levels of thefactors have been coded as +1 and −1, respectively,and the coded values of any intermediate levels canbe calculated using the following expression[12].

Xi = X− [(Xmax +Xmin)/2]/[(Xmax−Xmin)/2] (1)

where Xi is the required coded value of a factor forany value X from Xmin to Xmax; Xmin is the lower


Table 3(a) Chemical composition (wt pct) of base metal and all weld metal

Type of material Mg Mn Fe Si Cu AlBase metal (AA6061) 0.689 0.331 0.230 0.531 0.305 BalAll weld metal (AA4043) 0.050 0.220 0.050 5.0 0.120 Bal

Table 3(b) Mechanical properties of base metal and all weld metal

Type of material Yield strength Ultimate tensile strength Elongation Vickers hardness, 0.05 kg/MPa /MPa /(%)

Base metal (AA6061) 270 310 10 240All weld metal (AA4043) 140 210 7 260

level of the factor and Xmax is the upper level of thefactor.

2.4 Conducting the experiments and recording the re-sponses

The base metal used in this investigation is amedium strength aluminium alloy of AA6061 grade.The chemical composition of the base metal was ob-tained using a vacuum spectrometer (ARL-Model:3460). Sparks were ignited at various locations of thebase metal sample and their spectrum was analyzedfor estimation of the alloying elements. The chemi-cal composition of the base metal in weight percent isgiven in Table 3. The polarization test was carried outin non-deaerated 3.5% NaCl solution of pH 7. Analargrade chemicals and double distilled water were usedfor preparation of the electrolyte. The specimens wereprepared according to the metallographic standard.Specimens of 20 mm×40 mm (width and length) wereprepared to ensure the exposure of 10 mm diametercircular area in the weld region to the electrolyte. Therest of the area was covered with an acid resistant lac-quer. A potentiostat (Gill AC) was used for this studyin conjunction with an ASTM standard cell and per-sonal computer. The corrosion rate was calculated bypolarizing the specimen anodically and cathodicallyand by extrapolating the Tafel regions of anodic andcathodic curves to the corrosion potential. The inter-section of these two lines at the corrosion potentialyields the corrosion current density, icorr. The corro-sion potential and corrosion current density were ob-tained for each Tafel plot directly from the personalcomputer attached to the polarization set-up.

3. Mathematical Model

In order to represent the PCP of the joint, theresponse function can be expressed as follows[10–12].

PCP = f (peak current (P), base current (B),

pulse frequency (F ), pulse on time (T ))

PCP = f (P ,B ,F ,T ) (2)

The model selected includes the effects of mainfactors and first order interaction of all factors. Itis a portion of power series polynomial expressed asfollows.

PCP = b0 +b1(P )+b2(B)+b3(F )+b4(T )+b5(PB)+

b6(PF ) + b7(PT ) + b8(BF ) + b9(BT )+

b10(FT ) + b11(PBF ) + b12(PBT ) +

b13(PFT ) + b14(BFT ) + b15(PBFT ) (3)

where b0 is the average of responses (pitting corrosionpotential); b1, b2, b3,......b15 are the coefficients thatdepend on respective main and interaction factors andcan be calculated by following expression[10].

bi = Σ(Xi · Yi)/n (4)

where ‘i’ varies from 1 to n, in which Xi is the cor-responding coded value of a factor and Yi is the cor-responding response output value (pitting corrosionpotential) obtained from the experiment and ‘n’ isthe total number of combinations considered (in thiscase n=16).

Analysis of variance (ANOVA) method was ap-plied to find out the significance of main factors andinteraction factors. The higher order interactions (3and 4 factor interactions) are practically insignificantand hence not considered[13]. Yate′s algorithm wasused to calculate the sum of squares. Table 4 repre-sents the Yate′s algorithm and in the column marked(1), the upper half was obtained by adding successivepairs of treatments and the lower half by subtractingsuccessive pairs. Columns (2), (3) and (4) were ob-tained in the same manner from the entries in columns(1), (2) and (3), respectively. Each sum of square wasobtained by squaring the corresponding effect totaland dividing the result by r. 2nf , where ‘r’ is numberof replicates (trials) and ‘nf ’ is the number of chosenfactors. Further details regarding ANOVA methodand Yate′s algorithm can be found in literature[10,11].

3.1 Final mathematical modelANOVA test results are presented in Table 5.

From the ANOVA test results, it is evident that allthe main factors (P,B, F, T ) and few interaction fac-tors (BF and BT ) were considered to be significant.Hence the final model was developed including onlythese significant factors and given below.

(PCP) = {(−528) + 16.88(P)− 27.5(B) +

14.38(F )− 4.38(T ) + 6.88(BF )− 3.13(BT )}mV(5)

3.2 Checking adequacy of the developed modelCoefficient of correlation ‘r’ is used to find how

close the predicted and experimental values lie and itis calculated using the following expression.

r2 = Explained variation/Total variation =

Σ(PCPp − P̄CP)2/Σ(PCPe − P̄CP)2 (6)


Table 4 Yate′s algorithm to calculate sum of squares for pitting corrosion potential (PCP)

Y [1] [2] [3] [4] SS−500 −975 −2105 −4105 −8440 4E+06 1−475 −1130 −2000 −4335 270 4556.3 P−590 −955 −2230 135 −440 12100 B

[+] −540 −1045 −2105 135 −10 6.25 PB−495 −1055 75 −245 230 3306.3 F−460 −1175 60 −195 −20 25 PF−535 −1015 70 15 110 756.25 BF−510 −1090 65 −25 −20 25 PBF−550 25 −155 105 −230 3306.3 T−505 50 −90 125 0 0 PT−600 35 −120 −15 50 156.25 BT

[−] −575 25 −75 −5 −40 100 PBT−525 45 25 65 20 25 FT−490 25 −10 45 10 6.25 PFT−560 35 −20 −35 −20 25 BFT−530 30 −5 15 50 156.25 PBFT

Table 5 ANOVA (analysis of variance) test results for pitting corrosion potential

FactorsSum of squares (SS) Degrees of freedom (d.o.f.) Mean squares (SS/d.o.f.) Fratio (MS/error)

Main factorsP 4556.25 1 4556.25 72.9B 12100 1 12100 193.6F 3306.25 1 3306.25 52.9T 3306.25 1 3306.25 52.9

Two factors∗PB 6.25 1 6.25 0.1∗PF 25 1 25 0.4∗PT 0 1 0 0BF 756.25 1 756.25 12.1∗BT 156.25 1 156.25 2.5∗FT 25 1 25 0.4Error 312.5 5 62.5 –Total 24550 15 – –

Note: ∗F(1,5,0.95)=6.41. Therefore, PB, PF , PT , BT & FT are not significant at 95% confidence level

where PCPp is predicted (using the above model) pit-ting corrosion potential value for the given factors;PCPe is the experimental value for the correspond-ing factors; P̄CP is the average of experimental pit-ting corrosion potential values. The value of ‘r’ forthe above developed model is found to be 0.92, whichindicates high correlation between experimental andpredicted values.

4. Discussion

The mathematical model developed in the abovesection has been written in C program and the devel-oped C program has been used to estimate the pittingcorrosion potential of the pulsed current TIG weldedAA6061 aluminium alloy welds for different combi-nations of pulsed current parameters. Predicted val-ues were plotted and displayed in Fig.1. The plottedgraphs can be effectively used to understand the ef-fect of pulsed current parameter, such as peak current,base current, pulse frequency and pulse on time, onpitting corrosion resistance of TIG welded AA6061aluminium alloy joints. Figure 2 reveals the fusionzone microstructure of the welded joints.

4.1 Effect of pulsed current parameters on fusion zonegrain size

Solidification cracking occurs when the thermal

stresses built up during freezing exceed the strength ofthe solidifying weld metal. The commonly used meth-ods to reduce the tendency for solidification crackinginclude: altering weld metal composition, through theaddition of a filler wire, close process control, and con-trolling the grain structure within the fusion zone. Itis widely accepted that by changing the weld′s grainstructure, from coarse columar to fine equiaxed, bet-ter cohesion strength can be obtained, and the re-maining eutectic liquid present during the final stageof solidification can be fed more easily and the pre-formed cracks may be healed[14,15].

Another way of reducing the susceptibility to so-lidification cracking is through fusion zone grain re-finement, which confers the further benefit that theweld metal mechanical properties are improved. Var-ious grain refinement techniques have been discussedin the literature for aluminium alloy welds, e.g. elec-tromagnetic stirring, current pulsing, torch vibrationand inoculation. Of these, pulsed current weldingtechnique has gained wide popularity because of theirstriking promise and the relative ease with whichthese techniques can be applied to actual industrialsituations with only minor modifications to the exist-ing welding equipment[17].

In general, the formation of equiaxed grain struc-ture in CCTIG (continous current tungsten inert gas)weld is known to be difficult because of the remelting


Fig.1 Effect of pulsed current parameters on pitting corrosion potential

of heterogeneous nuclei or growth centers ahead of thesolid-liquid interface. This is due to the high tem-perature in the liquid, thus making survival nucleidifficult. The microstructural evolution in weld fu-sion zone is also influenced in many ways by currentpulsing, principally, the cyclic variations of energy in-put into the weld pool cause thermal fluctuations, oneconsequence of which is the periodic interruption inthe solidification process. As the pulse peak currentdecays the solid-liquid interface advances towards thearc and increasingly becomes vulnerable to any distur-bances in the arc form. As current increases again inthe subsequent pulse, growth is arrested and remelt-ing of the growing dendrites can also occur. Currentpulsing also results in periodic variations in the arcforces and hence an additional fluid flows that low-ers temperatures in front of the solidifying interface.Furthermore, the temperature fluctuations inherentin pulsed welding lead to a continual change in theweld pool size and shape favoring the growth of newgrains. It is also noted that effective heat input forunit volume of the weld pool would be considerablyless in pulse current welds, so the average weld pooltemperatures are expected to be low[16,17].

It is important to note that while dendrite frag-mentation has frequently been cited as a possiblemechanism, evidence for this has not been found. Itwas suggested that the mechanism of dendrite break-

up may not be effective in welding because of thesmall size of the fusion welds and the fine interden-drite spacing in the weld microstructure. Thus grainrefinement observed in the PCTIG welds is thereforebelieved to be due to other effects of pulsing on theweld pool shape, fluid flow and temperature. The con-tinual change in the weld pool shape is particularlyimportant. As the direction of maximum thermalgradient at the solid-liquid interface changes contin-uously, newer grains successively become favourablyoriented. Thus, while each grain grows only a smalldistance, more grains grow resulting in a fine-grainedstructure[14].

The weld pool solidification during fusion weldingbegins with the epitaxial growth of grains from par-tially melted zone grains along the fusion boundary,at the interface between the base metal and fusionzone. The partially melted grains provide excellentsites for growth with the growth rate exceeding thenucleation rate in this region. Epitaxial growth acrossthe weld pool results in long and oriented columnargrains. The epitaxial grains are the final result ofcontinuing growth of the partially melted grains fromthe fusion boundary. Epitaxial growth requires that aminimal degree of undercooling prevail. In contrast,the nucleation of new grains both at and near the fu-sion boundary necessitates a free energy barrier to beovercome. Consequently, no undercooling is necessary


Fig.2 Micrographs of fusion zone region: (a) Joint 1 (D=40 µm), (b) Joint 2 (D=30 µm), (c) Joint 3 (D=65 µm),(d) Joint 4 (D=55 µm), (e) Joint 5 (D=35 µm), (f) Joint 6 (D=20 µm), (g) Joint 7 (D=50 µm), (h) Joint8 (D=40 µm), (i) Joint 9 (D=55 µm), (j) Joint 10 (D=35 µm), (k) Joint 11 (D=75 µm), (l) Joint 12(D=60 µm), (m) Joint 13 (D=50 µm), (n) Joint 14 (D=30 µm), (o) Joint 15 (D=60 µm ), (p) Joint 16(D=45 µm)

for nucleation. To initiate nucleation in the weld de-posit and concurrently promote epitaxial grain refine-ment, it is essential to either increase the driving force,i.e. degree of undercooling, or reduce the free energybarrier by introducing trace amounts of zirconium ortitanium to the aluminium weld pool[18].

4.2 Effect of pulsed current parameters on pittingcorrosionThe microstructure of AA6061 exhibits inter-

metallics and strengthening particles. The inter-metallics are formed during casting and ingot homoge-nization due to interaction between alloying elementsand impurities present in the alloy. In AA6061 theMg2Si intermetallics undergo phase transformationand change their morphology during ingot homoge-nization, but they are not affected by solution heattreatment and aging of the alloy. The strengthen-ing particles have composition Mg2Si and size in thenanometer range. Their precipitation in the matrixduring aging provides strength to the alloy. In ad-dition, the strengthening particles precipitate at thegrain boundaries strongly affecting the resistance ofintergranular corrosion of the alloy[19,20].

However, Al7Cu2Fe and (Al,Cu)6(Fe,Cu) inter-

metallics are the initiation sites for pitting in Al-Zn-Mg-Cu alloys. The pitting is due to local dissolutionof the matrix or to dissolution of the intermetallics be-cause there is galvanic coupling between intermetallicsand matrix. The intermetallics containing Cu and Feare cathodic with respect to matrix and promote dis-solution of the matrix, while Mg-rich intermetallicsare anodic with respect to the matrix and dissolvepreferentially[21,22]. In general, the pitting corrosionresistance of AA6061 aluminium welds was found tobe lower than that of the base metal. This can be at-tributed to the presence of segregation products in assolidified welds. The poorest corrosion resistance ex-hibited by continuous current welds can be attributedto the presence of continuous network of grain bound-ary precipitates mainly containing magnesium rich ηphase. Region adjacent to the grain boundary is ex-pected to be depleted in magnesium due to the pres-ence of magnesium rich η at grain boundaries. Theseareas containing lower amounts of magnesium are thepreferred locations for corrosion.

A relatively more uniform distribution of pits wasobserved in pulsed current welds and this is due tothe absence of a continuous grain boundary precip-itates and to lower microsegregation of silicon and


magnesium in these welds. This could be attributedto convection in weld pool due to current pulsing. Thegrain boundary corrosion reported here is also simi-lar to weld decay generally observed in unstabilizedstainless steels due to depletion of chromium from lo-cations near the grain boundary as a consequence ofchromium carbide precipitation at the grain bound-ary.

Similar observations have also been made by otherinvestigators[8,23] in Al-Li alloy welded using AA5356filler metal. Further, they opined that the aging upto peak strength results in increased precipitation ofequilibrium η at the grain boundaries, thus providingnumerous anode-cathode cells. Overaging coarsensthe precipitates and also results in precipitate agglom-eration, leading to a reduction in the density of precip-itates as well as minimizing chemical inhomogeneityaround the precipitates due to diffusion effects. This,therefore, results in a relatively decreased tendencyfor corrosion in the overaged condition, as comparedto that in the underaged and peak aged conditions.

5. Conclusions

(1) Generally, peak current and pulse frequencyhave direct proportional relationship with the pittingcorrosion resistance of the welded joints, i.e. if thepeak current is increased, the pitting corrosion resis-tance will be increased. The similar effect is observed,when frequency is increased.

(2) Base current and pulse on time have inverseproportional relationship with the pitting corrosionresistance, i.e. if the base current is raised, the pittingcorrosion resistance will be decreased. The similar in-fluence is noticed when pulse on time is increased.

(3) The developed mathematical model can be ef-fectively used to predict the pitting corrosion poten-tial of PC TIG welded AA6061 aluminium alloy joints.

AcknowledgementsThe authors would like to thank Defence Research &

Development Organization (DRDO), New Delhi for thefinancial support rendered to carryout this investigation.The authors also would like to thank the Department ofManufacturing Engineering, Annamalai University for ex-tending the facilities of Metal Joining Laboratory and Ma-terial Testing Laboratory to carryout this investigation.

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