Enhanced ductility of the ZA85 magnesium alloy fabricated by equal-channel angular pressing

Abstract

Equal-channel angular pressing (ECAP) was applied to the as-cast Mg-8 wt.% Zn-5 wt.% Al (ZA85) alloy to produce a fine-grained structure with fine and uniformly distributed Mg-32 (Al, Zn)(49) (tau-phase) particles. Experiments showed that the ZA85 alloy had an initial grain size of similar to 150 mu m after casting and was significantly reduced to 4 mu m after six ECAP passes at 180 degrees C. After annealing at 300 degrees C for 1 h, the average grain size merely increased to 7.1 mu m. This thermal stability of the fine-grained structure at temperatures at or below 325 degrees C is attributed to the presence of the fine and well distributed tau-phase. It was demonstrated that ECAP processing greatly enhances ductility of the experimental alloy. By testing over a range of temperatures and strain rates, a maximum elongation to failure of 400% was obtained in the ECAP ZA85 alloy tested at 300 degrees C (0.53 T-m) with the initial strain rate of 1.0 x 10 (4) s (1). The dominant deformation mechanism for the specimens tested at 300 and 350 degrees C with the initial strain rates ranging from 1.0 x 10 (4) s (1) to 1.0 x 10 (3) s (1) is GBS controlled by grain boundary diffusion. At the higher testing temperature of 400 degrees C, the deformation mechanism for the experimental alloy is dislocation creep. (C) 2012 Elsevier B. V. All rights reserved.