Effect of grain size on the mechanisms of plastic deformation in wrought Mg–Zn–Zr alloy revealed by acoustic emission measurements

Abstract

The present study has clarified the roles of dislocation slip and twinning as the deformation mechanisms in magnesium alloys, as well as the effect of grain size on their relative contributions. The details of these mechanisms were studied by monitoring acoustic emission (AE) in conjunction with a novel signal categorization technique in Mg alloy ZK60. Through the analysis of AE time series the sequences of predominant deformation mechanisms in coarse grained (∼70μm) and fine grained (∼2μm) specimens of the alloy were identified with a high degree of confidence. It was found that dislocation slip and twinning occur during tensile loading simultaneously for both microstructural states of the material, while a change from one predominant mechanism to the other occurs in the course of loading. Specifically, in the fine grained material plastic deformation is initially carried by dislocation slip, but deformation twinning takes over as the lead mechanism early on. In the coarse grained variant this sequence is reversed. The implications of the changing roles of the mechanisms of plastic deformation for the overall mechanical performance of ZK60 in the two contrasting microstructural states are discussed.