Equal channel angular processing of magnesium alloys

Equal channel angular processing (ECAP) offers the potential to introduce very large strains into a workpiece without changing its cross-section. Hence, it is an attractive technique for developing homogeneous fine-grained metals with good forming characteristics. Magnesium alloys are ideal condidates to benefit from ECAP, because they exhibit poor low temperature forming characteristics due to a hexagonal close packed crystal structure. An assessment of the technique has been made with three commercial magnesium alloys ZK60, WE43 and AZ31 and one experimental alloy Mg-4wt%Li. The ductilities of the former two precipitation strengthened alloys, which contain Zr, were substantially improved. The latter two solid solution strengthened alloys, which do not contain Zr, showed little change in their properties for the processing conditions explored. Relative to the as-received material, the ductility of ZK60 was improved by at least 2 times over the entire temperature range investigated (24-450°C); with superplastic elongations up to 370%. Dynamic recrystallization appears to be an important mechanism for accommodating the high elongations. Comparisons are made with reported superplastic results from extruded Mg alloys.