Mechanical processing of two-phase alloys by severe plastic deformation

Equal channel angular pressing (ECAP) is a very promising method among several severe plastic deformation (SPD) processes since it offers a potential for high strain rate superplasticity by effective grain refinement to the level of the submicron or nanoscale. Therefore, microduplex alloys such as Zn-22% Al and Pb-62% Sn alloys were subjected to ECAP to study their mechanical properties by varying several parameters available during the ECAP process such as the pressing temperature and the number of pressings.; The Zn-22% Al alloy was subjected to ECAP at temperatures of 373 and 473 K with a number of pressings up to 4, 8 and 12 passes via route B _C where the sample is rotated by 90° in the same sense between each pressing. Superplasticity was promoted to a large extent for specimens pressed at both temperatures. It was realized that the number of pressings greatly influenced the superplasticity in the Zn-22% Al alloy such that the peak strain rate as well as the ductility tended to be enhanced with increasing numbers of pressings.; The microstructure in the Zn-22% Al alloy was studied after the ECAP process. Similar phases were agglomerated at the low numbers of pressings but agglomeration tended to disappear at higher numbers of pressings. It was considered that true mixing of two different phases aided the superplasticity since the mechanical results showed that superplasticity was progressively enhanced as the agglomeration decreased.; A study of the effect of the number of pressings on the strength of the Zn-22% Al alloy showed that the deformation occurred during microindentation in the high temperature deformation regime rather than by the Hall-Petch relationship. A two-dimensional measurement of microhardness on the surface of the cross-section of the billet also showed that friction between the billet and the die surface introduced a local variation in hardness.; A Pb-62% Sn eutectic alloy was subjected to ECAP up to 4, 8 and 16 passes via route B_C. It is shown that superplasticity is not much enhanced in this alloy due to a less effective grain refinement in this alloy.