Microstructural evolution of rolled AZ31 alloy plate during in-plane compression and annealing: Effect of amount of compressive strain

Abstract In this study, a rolled AZ31 alloy plate is compressed to various plastic strains (3, 6, and 9%) along the rolling direction (RD) and then annealed at 250 °C to determine the variations in the microstructural characteristics during the compression and subsequent annealing steps. When 3% compression is applied to the as-rolled material, its average grain size decreases from 37.9 μm to 18.8 μm because of the formation of numerous lamellar { 10 1 ‾ 2 } twin bands. However, as the compressive strain increases from 3% to 9%, the average grain size increases from 18.8 μm to 31.6 μm owing to the coalescence of the formed twin bands. An increase in the compressive strain leads to the gradual strengthening of the RD-oriented twin texture, in which the basal poles are distributed within a range of 0°–43° from the RD toward the transverse direction. The subsequent annealing treatment causes an increase in the average grain size and a decrease in the number fractions of twin-induced boundaries with misorientation angles in the ranges of 5°–10°, 50°–60°, and 80°–90° owing to the formation of twin-free grains. The grain coarsening during annealing is much less pronounced in the 9%-compressed material than in 3%-compressed material because the driving force for boundary migration is lower in the former owing to the more homogeneous distribution of internal strain energy. The annealing treatment does not cause a remarkable change in the texture of the compressed materials. The 9%-compressed and subsequently annealed material has a spread RD-oriented texture and consists of twin-free equiaxed grains smaller than those of the as-rolled material. These results demonstrate that the application of an appropriate combined process of in-plane compression and subsequent annealing enables effective modification of the texture of rolled Mg alloy plates without any change in their twin-free homogeneous grain structure.