Abnormal grain growth through cyclic heat treatment in a Mg–Sc alloy

Abstract

Enlarging the grain size in Mg–Sc alloys can greatly improve superelasticity. The impact of heat treatment conditions on abnormal grain growth (AGG) caused by phase transformation through cyclic heat treatment (CHT) was investigated in this study. In the CHT process between temperatures in a β single-phase region (Tβ) and α + β two-phase region (Tα+β), lowering the Tα+β resulted in a uniform huge grain size after AGG. In the heating process of the CHT from the Tα+β to the Tβ, the decrease in the heating rate was found to be ineffective in realizing huge grain size because the number of grains that can start AGG increases, which causes the collision of the abnormally growing grains with each other. We also revealed one of the key factors for the AGG to occur. Subgrains, which were formed through CHT, not only act as an additional driving force for grain growth but also shorten the required time for AGG nucleation.