VLIV GEOMETRIE NÁSTROJE ECAP NA DOSAŽENÉ ZJEMNĚNÍ ZRNA

1. METAL 2008 Hradec nad Moravicí květen 19 – 21. 2009 VLIV GEOMETRIE NÁSTROJE ECAP NA DOSAŽENÉ ZJEMNĚNÍ ZRNA INFLUENCE OF ECAP DIE GEOMETRY ON ACHIEVED UFG 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

2. Introduction • Preparation of materials with ultra-fine-grained structure to nano-structure with mean size of grain below 1 mmis 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

3. 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)

4. Yield stress (MPa) Elongation (%) Fig. 1 Comparison of yield value of UFG and CG materials

5. Principle of the Equal Channel Angular Pressing(ECAP) p Fig. 2 Channel angles Fig. 3 Channel parameters R1 – outer radius R2 – inner radius b – channel width b1– channel width between sphericities p - load  - angle of transition of 2 channels y- angle of outside sphericity of the channel

6. 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

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

8. Proposed design of extrusion tool with the axis of the output part offset by 10° and 20° R1 = 4 mm, R2 = 0.5 mm, R5 = 5 mm  = 90°,  = 90° Offset axis by 10° Offset axis by20°

9. Effective Plastic Strain of the alloy AlMn1Cu at 20°C and 4 passes – classical channel Effective Plastic Strain Effective Plastic Strain 2nd pass 1st pass Effective Plastic Strain Effective Plastic Strain 3rd pass 4th pass

10. Effective Plastic Strain of the alloy AlMn1Cu at 20°C and 4 passes, channel deflection 20° Effective Plastic Strain Effective Plastic Strain 1st pass 2nd pass Effective Plastic Strain Effective Plastic Strain 3rd pass 4th pass

11. Overall comparison of results At present a simulation of the 5thpass was realised. Obtained magnitude of effective plastic strain is given in the table below. Obtained values of Effective Plastic Strain in dependence on channel geometry and number of passes

12. Insert of the ECAP tool with deflection of 20°

13. Shapes of the sample after individual passes through the ECAP channel

14. Influence of channel deflection on strengthhening 1st- 5thpass (experimental results)

17. Strengthening (MPa)

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

21. 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 strengtheningat deflection of the channel by 20° at the 1st and 2ndpass 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.

22. 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 analysis TEM analysis

23. Micro-structural analysis after the 5thpass, central part of the sample at cross section – classical ECAP tool SAED analysis TEM analysis

24. Analysis of the obtained grain size after the 1stpass at cross section of the sample prepared by the classical ECAP tool with deflection of horizontal part of the channel by 20° SAED analysis TEM analysis

25. Analysis of the obtained grain size after the 5thpass at cross section of the sample prepared by the classical ECAP tool with deflection of horizontal part of the channel by 20° SAED analysis TEM analysis

26. 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 5thpass. • Initial mean grain size was within the interval from 100 to 150 mm. After the 5thpass 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 isnot 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.

27. 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 5thpass 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.

28. 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

29. Proposed design of extrusion tool with helix in vertical part of the channel R1 = 4 mm, R2 = 0.5 mm  = 90°,  = 90°

30. Laboratory equipment for development of UFG materials Hydraulic press DP 1600 kN

31. Control panel for settings of the forming parameters Forming die with heating cuff

32. Service cylinder heating furnace designedfor the temperature 1100°C

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

34. Proposed design – side view

35. 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).

36. Equipment of the type CONFORM

37. 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 -150mm.

38. Thank you for your attention