Effect of annealing on the microstructure and mechanical anisotropy of Mg/Al composite plate

In this paper, the effects of recrystallization, grain growth and texture evolution on the formability and anisotropy of Mg/Al composite plates were studied by different annealing processes. The results show that the rolled Mg/Al composite plate exhibits obvious anisotropy and poor formability in the rolling directions (RD) and transverse directions (TD), which is the result of the synergistic effect of matrix texture and grain characteristics. Annealing-activated recrystallization can eliminate local shear bands, hardening and other defects formed by rolling, thereby softening the structure and improving the formability of the sheet. The occurrence of recrystallization behavior also makes the bimodal texture parallel to the TD distribution in the Mg matrix transform into the RD-TD surface dispersion distribution, which weakens the strong deformation texture. The Schmidt factor (SF) of each slip system is calculated to evaluate the slip system start-up probability (deformation difficulty) of the material in a certain direction. The results show that the average SF values of matrix slip in RD and TD directions increase after annealing treatment, which makes the slip system easier to start. The tensile test results show that the formability of the composite plate is the best when the annealing temperature is 300 °C. At this time, the ultimate tensile strength (UTS) and yield strength (YS) are small, the elongation (EL) is large and the anisotropy of mechanical properties is the weakest. In addition, the annealing of the composite plate leads to the transformation of the fracture mechanism from brittle fracture to ductile-brittle mixed fracture. In summary, annealing treatment can effectively improve the formability and weaken the anisotropy of Mg/Al composite plates.