Enhanced stretch formability of AZ31 magnesium alloy thin sheet by pre-crossed twinning lamellas induced static recrystallizations

In order to improve the stretch formability of AZ31 magnesium alloy thin sheet with thickness of 1 mm, a multidirectional pre-compressive deformation along rolling (RD)-transverse direction (TD) with various strain levels and sequent annealing at 450 °C are conducted. Besides, a special die is developed to avoid sheet bending-buckling during pre-compression. After TD-RD multidirectional pre-compression (T1.69%-R3.3%, T3.32%-R3.3%, T5.38%-R3.3%) and annealing, the grain size increases obviously with increasing TD pre-strain levels which may be related to the strain induced static recrystallization. However, grain coarsening was observed in R3.3%-T1.59% pre-compressed Mg sheets and then the grain size decreased gradually as the TD pre-strain levels increased (R3.3%-T1.69%, R3.3%-T3.32%, R3.3%-T5.38%). The microstructure evolution in the multidirectional pre-compression Mg sheets may be attributed to the twin-twin intersections serving as nucleation sits further to promote the recrystallization behavior. Due to the pre-induced twins and grain growth, the (0002) basal texture weakens obviously. The stretch formability (IE-value) of magnesium alloy sheet is enhanced greatly with the IE-value being improved by 112.4% in T5.38%-R3.3% pre-compressed Mg alloy sheet compare to that of as-received one.