VLIV GEOMETRIE NÁSTROJE ECAP NA VLIV GEOMETRIE NÁSTROJE ECAP NA DOSAŽENÉ ZJEMNĚNÍ ZRNADOSAŽENÉ ZJEMNĚNÍ ZRNA

Stanislav Rusz*, Jan Dutkiewicz**,Lubomír Čížek*,Jiří Hluchník*, Irena Skotnicová*

* VŠB – Technická univerzita Ostrava,, Fakulta strojn Česká Republika

** Polska Akademia Nauk, Instytut Metalurgii i Badań Materialów, Kraków, Polsko

INFLUENCE OF ECAP DIE GEOMETRY ON ACHIEVED INFLUENCE OF ECAP DIE GEOMETRY ON ACHIEVED UFGUFG

METAL 2008

Hradec nad Moravicí květen 19 – 21. 2009

Introduction

• Preparation of materials with ultra-fine-grained structure to nano-structure with mean size of grain below 1m is one of progressive technologies, which was for last approx. 15 years in the centre of interest of basic and applied research. It is expected that such materials will have high strength properties, as well as good forming parameters, overcoming the properties of currently produced classical materials

• Some types of ultra-fine-grained (UFG) alloys have already been implemented into mass production, whereas required properties are achieved by formation of fine-grained structure and its stabilisation. At the same time further intensive research of completely novel production technologies is carried on. It should be noted that one of the ways for obtaining ultra-fine-grained structure or nano-structure consists in use of severe plastic deformation of materials, i.e. amount of deformation, which cannot be obtained by classical deformation processes

• It is known that grain refinement improves mechanical strength, it is therefore obvious that UFG materials have very high strength. Moreover, these materials have at the beginning high density of dislocations. UFG materials can achieve after the SPD process higher strengthening. This process, however, usually reduces ductility

• Recent investigations have shown that UFG materials uniquely combine high strength and ductility (Fig. 1), but this success requires original approach

• Two connecting lines in the diagram represent this dependency for Cu and Al. Percentage marking in the nodes denotes percentage reduction of the mean grain size after individual passes through the ECAP tool. Unlike this, extremely high strength and ductility of nano-crystalline Cu and Ti evidently differentiates these materials from coarse-grained metals (CG)

Fig. 1 Comparison of yield value of UFG and CG materials

Principle of the Equal Channel Angular Pressing (ECAP)

p - load - angle of transition of 2 channels- angle of outside sphericity of the channel

R1 – outer radiusR2 – inner radiusb – channel widthb1 – channel width between sphericities

Fig. 3 Channel parametersFig. 2 Channel angles

p

Mathematical simulation of forming process by the program QForm

• This product has been based on advanced software and forming technologies

• Results of simulation are displayed simultaneously with progress of simulation. Model of metal forming realised in the QForm program corresponds to real forming process. Simulation gives complete information about distribution of flows, temperatures and deformation in material, about force, energy and other parameters of the forming process

New concept of design of the ECAP tool – deflection of horizontal part by 10° and 20°

Offset axis by 10° Offset axis by 20°

Axis offset of the output part [°]

Intensity of strain [-]

0 1

10 1.25

20 1.4

R1 = 4 mm, R2 = 0.5 mm, R5 = 5 mm = 90°, = 90°

Proposed design of extrusion tool with the axis Proposed design of extrusion tool with the axis of the of the output part offset by 10° and 20output part offset by 10° and 20°°

Effective Plastic Strain of the alloy AlMn1Cu at 20°C and 4 passes – classical channel

11stst pass pass 22ndnd pass pass

33rdrd pass pass 4th pass

Effective Plastic Strain

Effective Plastic Strain

Effective Plastic Strain

Effective Plastic Strain

Effective Plastic Strain of the alloy AlMn1Cu at 20°C and 4 passes, channel deflection 20°

11stst pass pass 22ndnd pass pass

33rdrd pass pass 44thth pass pass

Effective Plastic StrainEffective Plastic Strain

Effective Plastic StrainEffective Plastic Strain

Overall comparison of results

At present a simulation of the 5th pass was realised. Obtained magnitude of effective plastic strain is given in the table below.

Pass „Bc“

Temperature / channel deflection

1. 2. 3. 4. 5.

20°C/ 0° - deflection 1.15 2.1 2.9 3.5 4.1

20°C/ 20°- deflection 1.25 2.3 3.3 4.2 5.1

Obtained values of Effective Plastic Strain in dependence on channel geometry and number of passes

Insert of the ECAP tool with deflection of 20°

Shapes of the sample after individual passes through the ECAP channel

Influence of channel deflection on strengthhening 1st - 5th pass (experimental results)

AlMn1Cu alloy 1st pass, deflection (0, 10, 20) deg

050

100150200250300350400450500550

0 10 20 30 40 50

h [mm]

s [

MP

a] 10 deg

20 deg

0 deg

AlMn1Cu alloy 2nd pass, deflection (0, 10, 20) deg

050

100150200250300350400450500550600

0 10 20 30 40

h [mm]

σ [

MP

a] 0 deg

10 deg

20 deg

AlMn1Cu alloy 3rd pass, deflection (0, 10, 20) deg

0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

0 5 10 15 20 25 30 35 40 45

h [mm]

σ [

MP

a] 0 deg

10 deg

20 deg

AlMn1Cu alloy 5th pass, deflection (0, 10, 20) deg

050

100150200250300350400450500550600650700750800

0 5 10 15 20 25 30 35 40 45

h [mm]

σ [

MP

a]

0 deg

10 deg

20 deg

AlMn1Cu alloy 4th pass, deflection (0, 10, 20) deg

050

100150200250300350400450500550600650700750800

0 5 10 15 20 25 30 35 40 45

h [mm]

σ [

MP

a]

0 deg

10 deg

20 deg

Strengthening (MPa)

Channel deflection/no. passes

1st pass 2nd pass 3rd pass 4thpass 5th pass

0° 430 448 456 464 500

10° 460 472 640 772 790

20° 500 574 642 775 795

Influence of number of passes on magnitude of strengthhening for various designs of the ECAP tool

AlMn1Cu alloy, 0 deg (channel deflection)

050

100150200250300350400450500550

0 5 10 15 20 25 30 35 40 45 50

h [mm]

s [

MP

a]

2nd pass

1st pass

3rd pass

4th pass

5th pass

AlMn1Cu alloy, 10 deg (channel deflection)

050

100150200250300350400450500550600

0 5 10 15 20 25 30 35 40 45

h [mm]

σ [

MP

a]

1st pass

2nd pass

3rd pass

4th pass

5th pass

AlMn1Cu alloy, 20 deg (channel deflection)

050

100150200250300350400450500550600650700750800

0 5 10 15 20 25 30 35 40 45

h [mm]

σ [M

Pa]

1st pass

2nd pass

3rd pass

4th pass

5th pass

Summary of partial results

• The obtained results have confirmed unequivocally big influence of modification of the ECAP tool design (channel deflection by 10° and 20°) on increase of resistance to deformation and thus strengthening of the given alloy at individual passes.

• Increase of strengthening at deflection of the channel by 20° at the 1st and 2nd pass is a very important finding as it gives a presumed possibility of reduction of overall number of passes.

• The results will be verified by next mechanical tests and metallographic analysis.

Micro-structural analysis on TEM and SAED

Analysis of the obtained grain size after the 1st pass at cross section of the sample prepared by classical ECAP tool

SAED analysisTEM analysis

Micro-structural analysis after the 5th pass, central part of the sample at cross section – classical ECAP tool

TEM analysis SAED analysis

Analysis of the obtained grain size after the 1st pass at cross section of the sample prepared by the classical ECAP tool with deflection

of horizontal part of the channel by 20°

TEM analysis SAED analysis

Analysis of the obtained grain size after the 5th pass at cross section of the sample prepared by the classical ECAP tool with deflection of horizontal part of

the channel by 20°

TEM analysis SAED analysis

Partial evaluation of micro-structure• It is evident from the shown pictures from  TEM and SAED, that

refinement of initial structure occurs both with use of the classical design of the ECAP tool, as well as with use of its modification, particularly after the 5th pass.

• Initial mean grain size was within the interval from 100 to 150 m. After the 5th pass the mean grains size achieved with classic al tool was within 500 – 600 nm.

• In case of new design of the tool with deflection of horizontal part of the channel by 20° the achieved refinement of mean grain size was within 200 – 300 nm.

• Structure is not homogennous in full volume of the sample.

• It is evident from the SAED analysis, that we have achieved a substantial increase of magnitude of angles of grain boundaries.

Influence of modification of the channel design on development of resistance to deformation

• Influence of change of the deformation route given by deflection of horizontal part of the channel of the ECAP tool by 10° and 20° in respect to classical design was proven unequivocally.

• At channel deflection by 20° there occurs at the 5th pass an increase of the maximum of resistance to deformation by 40% in comparison with deflection by 10°, and in comparison with classic al design when deflection is 0°, the maximum of resistance to deformation was increased by 60%.

• This brings a substantial increase in efficiency of the ECAP process.

Proposal of modification of horizontal part of the ECAP channel

• In order to increase the intensity of strain at the first pass through the ECAP tool, it was proposed to implement a helix into its horizontal part.

• At present manufacture of the ECAP tool with the proposed modification is being prepared with initial size of the extruded sample 15x15x65 mm

• Mathematical simulation of extrusion is shown in the next figure

Turning of vertical part [°] Intensity of strain [-]

60 1.35

R1 = 4 mm, R2 = 0.5 mm

= 90°, = 90°

Proposed design of extrusion tool with helix in vertical Proposed design of extrusion tool with helix in vertical part of the channelpart of the channel

Laboratory equipment for development Laboratory equipment for development of UFG materialsof UFG materials

Hydraulic press DP 1600 kN

Control panel for settings of the forming parameters

Forming die with heating cuff

Service cylinder heating furnace designed for the temperature 1100°C

Proposed design of the prototype of equipment for development of UFG structure in a strip of sheet

Proposed design – side view

Principle of the proposal of new concept of the CONFORM type tool for extrusion of a strip of sheet

• The equipment consists of the following main functional parts: main working roll (pos. 4), 2 pressure rollers (pos. 5) with spacing plate (pos. 20), the extrusion tool consisting of two parts (pos. 17, 18) and 2 gripping plates (pos. 1, 2).

• Strip of sheet with dimensions 60 x 1.5 x 1000 mm is inserted by the force exerted by the working roll into the forming tool. The driven pressure rollers at the same time increase overall extrusion force. At the final stage the strip of sheet is drawn from the equipment by special jaw controlled by hydraulic cylinder (this is an independent equipment, which is not shown in drawings.) It is a prototype under development.

• The equipment is at present already manufactured and first verification trials are running (see the next figure).

Equipment of the type CONFORM

Final conclusion

● Growth of deformation intensity was obtained at extrusion of sample alloys through the ECAP tool after multiple passes. In conformity with theoretical assumptions greater number of passes results in substantial growth of intensity of strain.

● No influence of temperature on obtained deformation intensity was detected after individual passes.

● Modified tool geometry aimed at increase of the value of effective plastic strain (20° offset of horizontal part of the channel) enabled substantial increase of the sample deformation already after the first pass and subsequent passes through the ECAP tool, which contributes significantly to enhancement of the SPD process efficiency. This value achieves 16-18% of growth at individual passes.

● According to the input analysis of microstructure of extruded samples the process brought substantial refinement of grain to the final size d = 250-300 nm, from the input grain size 100 -150 m.

Thank you for your attention