Effects of Annealing Process on the Interface of Alternate α/β Mg-Li Composite Sheets Prepared by Accumulative Roll Bonding

Effects of annealing temperature and annealing time on the microstructure, interfacial bonding properties and mechanical properties of alternate α/β Mg-Li alloy composite plates by accumulative roll bonding (ARB) were investigated. Due to the large reduction, a part of the relatively harder Mg-5Li-1Al alloy is embedded into the softer Mg-12Li-1Al alloy to achieve metallurgical bonding in the process of composite rolling. The optimum annealing temperature of the composite plate is 350 °C or 400 °C. At the same time, the formation mechanism of the interfacial diffusion region was discussed, and results show that there exist two diffusion regions, diffusion layer 1 and diffusion layer 2. The diffusion layer 1 is mainly composed of Li₃Mg₇ phase, and the diffusion layer 2 is composed of Li_0.92Mg_4.08 phase. The interfacial bonding ability of Mg-Li alloy composite plate first increases and then decreases with the increase of annealing temperature and annealing time. Compared with the composite plate processed by one pass ARB, the annealing time of the composite plate processed by six passes ARB increases due to the increase of cumulative strain, and the optimum annealing process is at 400 °C for 30 min.