It is well known that application of severe plastic deformation (SPD) in con- ventional deformation processing techniques such as rolling, drawing, and extrusion leads to a signi fi cantly higher strength and a relatively low ductility. SPD processing using ECAP leads to reduction in the ductility which is generally less than in more conventional deformation processing techniques. For example, experiments con- ducted to compare the strength and ductility of the 3004 aluminum alloy processed by ECAP and cold-rolling [ 3 ] showed that the yield strength increased monotoni- cally with the increasing equivalent strain imparted into the alloy by either cold rolling or ECAP (Fig. 1.1 ). It is apparent also that the overall ductility exhibits different trends for these two processing methods. After one ECAP pass, equivalent to a strain of * 1, the elongation to failure or the ductility of the alloy decreases from * 32 to * 14 %. However, there is no additional reduction in the ductility with additional ECAP passes and therefore with the imposition of even larger strains. By contrast, cold-rolling decreases ductility by a similar magnitude initially but there- after the ductility continues to decrease with increasing rolling strain, although at a Fig. 1.1 A comparison of yield strength and ductility for an Al-3004 alloy processed by cold-rolling or ECAP 2 V.P. Astakhov
slower rate. Consequently, processing by ECAP leads ultimately to greater retention of ductility than conventional cold-rolling. Recent fi ndings of extraordinary high strength and good ductility in several bulk ultra fi ne-grained metals produced by severe plastic deformation are well analyzed by Valiev and Langdon [ 4 ]. Superplasticity , i.e., obtaining a signi fi cant increase in the strain at fracture in certain work materials. For example, as reported by Figueiredoa and Langdon [ 5 ], mechanical testing of extruded ZK60 alloy at temperature of 473 K showed that the elongation at fracture was 830 % for a received material, whereas this became 3050 % after two passes through equal channel extrusion die. As reported by Kawasaki et al. [ 6 ], testing of a Pb-62 % Sn eutectic alloy after four passes through an equal channel extrusion die showed superplastic elongations at intermediate strain rates with a maximum elongation to failure of 2,665 %. Musin et al. [ 7 ] reported superplastic behavior of an Al – 4.1 %Mg – 2.0 %Li – 0.16 %Sc – 0.07 %Zr alloy (1421 Al) subjected to intense plastic straining by equal channel angular extrusion in the temperature interval 250 – 450 ° C at strain rates ranging from 1.4 × 10 − 5 to 1.4 s − 1 . The grain size after ECAE was about 0.8 μ m and the fraction of high angle boundaries was about 80 pct. The highest elongation of 1850 % without failure appeared at a temperature of 400 ° C and strain rate of 1.4 × 10 − 2 s − 1 .