Microstructure evolution and texture development in thermomechanically processed Mg–Li–Al based alloys

In the present study, the influence of alloying and thermomechanical processing on the microstructure and texture evolution on the two Mg–Li–Al based alloys, namely Mg–9 wt% Li–7 wt% Al–1 wt% Sn (LAT971) and Mg–9 wt% Li–5 wt% Al–3 wt% Sn–1 wt% Zn (LATZ9531) has been elicited. Novel Mg–Li–Al based alloys were cast (induction melting under protective atmosphere) followed by hot rolling at ∼573 K with a cumulative reduction of five. A contrary dual phase dendritic microstructure rich in α-Mg, instead of β-Li phase predicted by equilibrium phase diagram of Mg–Li binary alloy was observed. Preferential presence of Mg–Li–Sn primary precipitates (size 4–10 μm) within α-Mg phase and Mg–Li–Al secondary precipitates (<3 μm) interspersed in β-Li indicated their degree of dissolution during hot-rolling and homogenization in the dual phase matrix. Presence of Al, Sn and Zn alloying elements in the Mg–Li based alloy has resulted an unusual dual-phase microstructure, change in the lattice parameter, and intriguing texture evolution after hot-rolling of cast LAT 971 and LATZ9531 alloy. Strong texture was absent in the as-cast samples whereas texture development after hot-rolling revealed an increased activity of the non-basal ( 1   0   1 ¯   0 ) slip planes. The quantification of the grain average misorientation (less than 2°) using electron backscattered diffraction confirmed the presence of strain free grains in majority of the grains (fraction >0.75) after hot-rolling of Mg–Li–Al based alloys. Role of alloying in rendering distribution of dual-phase structure has strongly influenced dynamic-recrystallization and grain-growth in the hot-rolled Mg–Li–Al based alloys.