Influence of grain size on elongation at elevated temperatures in AZ31 Mg alloy

Abstract

Mechanical properties of an AZ31 Mg alloy with the grain sizes of 4, 12, 60 and 450 μm were investigated by tensile tests at 473-673 K with 1.7 × 10-5-1.7 × 10-1 s-1. The Mg alloy exhibited unique behaviors of low elongation of 17% at 473 K with 1.7 × 10-1 s-1 for the specimen with the grain size of 450 μm and large elongation of 234% at 673 K with 1.7 × 10-5 s-1 for the specimen with the grain size of 60 μm. These behaviors could not be explained from the viewpoint of the plastic stability. Microstructural observation revealed significant twin formation at 473 K with 1.7 × 10-1 s-1 for the specimen with the grain size of 450 μm and active grain boundary sliding at 673 K with 1.7 × 10-5 s-1 for the specimen with the grain size of 60 μm. Therefore, it is likely that enhancement of twining and grain boundary sliding gave rise to the unique behaviors of the Mg alloy that could not be explained from the plastic stability.