Twinning-assisted static recrystallization and texture evolution in a Mg-Gd-Y-Zr alloy.

Abstract

The formability and mechanical properties of magnesium (Mg) alloys are strongly related to the crystallographic basal texture. Twins play critical roles in adjusting crystallographic orientation of grains during both deformation and annealing treatment via deformation twinning and twinning-assisted recrystallization. In this study, cold rolling and subsequent annealing were conducted on a Mg-5.9Gd-3.3Y-0.5Zr alloy to investigate the recrystallization behavior and texture evolution. Electron backscatter diffraction and transmission electron microscopy techniques were applied to characterize the nucleation of recrystallized grains, especially the twinning-assisted recrystallization, at multi-scales. The results indicated that a large number of {10-12}, {10-11} twins and {10-11} - {10-12} double twins were introduced after cold rolling. The {10-11} - {10-12} double twins, double twin - grain boundary intersections and dense twin-twin intersections acted as the preferential nucleation sites for recrystallization during annealing treatment, while the coarse and parallel {10-12} twins were unfavorable for the nucleation of recrystallized grains. Although {10-12} tension twins are the most common twins in Mg alloys, the interface of this type of twin has strong mobility and is easy to expand. Therefore, it is generally difficult for a single {10-12} twin to recrystallize. However, the {10-11} compression twins and {10-11} - {10-12} double twins are generally difficult to expand and can store high deformation energy, so they are conducive to becoming nucleation sites for recrystallization. During the recrystallization process, the texture type (basal texture) of the cold rolled sample remained unchanged, but the overall texture intensity was significantly reduced due to the dispersion of grain orientations brought by new grains generated by twinning recrystallization.