Developing superplasticity in a magnesium alloy through a combination of extrusion and ECAP

A new processing procedure was applied to a cast Mg-9% Al alloy. This procedure involves the sequential application of extrusion and equal-channel angular pressing and is designated EX-ECAP. Experiments show that the Mg-9% Al alloy has an initial grain size of similar to50 mum after casting but this is reduced to similar to12 mum after extrusion and it is further reduced to similar to0.7 mum when the extruded alloy is subjected to ECAP for 2 passes at 473 K. Although the cast alloy exhibits extremely limited ductility and the extruded alloy is only moderately ductile, it is demonstrated that processing by EX-ECAP produces excellent superplastic ductilities including the occurrence of both low temperature superplasticity and high strain rate superplasticity. The EX-ECAP process is less effective when the ECAP step is conducted at 573 K because, although the pressing is then very easy, there is significant grain growth at this higher temperature. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.