Microstructural evolution of rolled Mg-5Zn-3Nd(-Zr) alloy

A mini-type rolling machine was employed for multi-passes rolling of a Mg-5Zn-3Nd(-Zr)(mass fraction, %) wrought alloy. For the sake of providing experimental basis for magnesium alloy rolling process, optical microscopy, SEM and TEM observations were used to study the microstructure evolution of magnesium alloys subjected to different rolling reductions before and after annealing. Investigations show that multi-passes can be achieved for this alloy at ambient temperature, but 330 °C, 15 min annealing was needed for next pass rolling, and total deformation degree was 66%. With the increase in total deformation degree, rolling streams form and the average grain size decreases gradually. The microstructure after rolling is mainly composed of twining, and multiple twining in parallel distribution is also observed. The average grain size in the as-cast condition is about 50 μm and decreases to about 10–20 μm after rolling, whereas the twinning spacing is limited to 1–2 μm. SAED analysis in the twinning area indicates that twinning takes place at {101} plane. Complete recrystallization can occur in Mg-5Zn-3Nd(-Zr) alloys with various rolling reductions and after 200 °C, 120 min or 300 °C, 10 min annealing. Meanwhile, grain growth is apparent under heat treatment at 300 °C.