Study on Microstructure and Mechanical Properties of AZ31 Alloy after Multi-pass Warm Rolling and Subsequent Annealing

The microstructure evolution and mechanical properties at room temperature of AZ31 sheet after warm rolling and subsequent annealing were investigated by SEM, TEM and tensile tests. The results show that a large number of parallel twins are produced in grains after warm rolling with the thickness reduction of 82%, and the tensile strength and the yield strength of the rolled sheet reach 364 MPa and 297 MPa, respectively, with the elongation of 8.4% at room temperature. With annealing time increasing at 200 ℃, twins disappear gradually and static recrystallization occurs more thoroughly in the rolled sheet. The smallest and uniform microstructure full of recrystallized grains with an average size of 5.3 μm is obtained in the rolled alloy after annealing for 30 min, and the tensile strength and the yield strength at room temperature of the annealed alloy are 323 MPa and 222 MPa, respectively, and the elongation at room temperature is 12.6%.