Significant Texture Weakening of AZ91 Alloy by Asymmetric Hot Rolling

The asymmetric hot rolling was applied to the as-cast AZ91 alloy to weaken the texture. It was found that the {0001} basal slip was not favored during deformation due to the presence of a strong 〈0001〉 orientation in the as-cast sample. Surprisingly, the fraction of contraction twins was much larger than extension ones owing to the high content of Mg₁₇Al₁₂ intermetallic compounds. The incoherent Mg₁₇Al₁₂ at the grain boundaries could limit and/or prevent the nucleation of the thick extension twin, but did not hinder the narrower twin (contraction and double) nucleation. A large amount of β phase within α grains provided more possibilities to reduce twin boundary migration, and thus, the growth of thick extension twins was hindered. The presence of the Mg₁₇Al₁₂ phase in the starting material was responsible for changing the twinning process. The asymmetric hot rolling led to significant texture weakening in the AZ91 alloy.