The Interaction Between $$ \{ 10\bar{1}2\} $$ Twinning and Long-Period Stacking Ordered (LPSO) Phase During Hot Rolling and Annealing Process of a Mg-Gd-Y-Zn-Zr Alloy

Abstract

The interaction between $$ \{ 10\bar{1}2\} $$ twinning and the LPSO phase was explored in the microstructure of a hot-rolled Mg-5.5Gd-4.4Y-1.1Zn-0.5Zr (wt pct) sheet. The twinning behavior in the nanoscale matrix lamellae, which were sandwiched between LPSO plates, was analyzed using high-resolution transmission electron microscopy. Profuse $$ \{ 10\bar{1}2\} $$ twinning is activated within grains containing the LPSO phase. Twinning easily occurs in the matrix with sparsely distributed LPSO plates, and the twins continually “traverse” across multiple LPSO plates. The occurrence of $$ \{ 10\bar{1}2\} $$ twinning in the matrix lamellae sandwiched between LPSO plates has a significant nanosize effect. With the decrease of matrix lamellae thickness, the nucleation and growth of twins become more difficult. Non-twinned matrix lamellae are found when the lamellae thickness is smaller than 50 nm. Additionally, the LPSO plates, which have been engulfed by twins, exist stably inside the twin after 10 pct hot rolling reduction at the temperature of 450 °C, and decompose during the annealing process. For the multi-pass hot rolling, the decomposition of the LPSO plates during intermediate annealing is considered to be beneficial for the continuous twin growth in the subsequent rolling pass, due to the relaxation of back-stress.