Interface microstructure evolution and bonding mechanism during vacuum hot pressing bonding of 2A12 aluminum alloy

The vacuum hot pressing bonding test of 2A12 aluminum alloy were performed under different temperatures (with 17.5% deformation). The microstructure evolution was characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM), and the interface bonding mechanism at elevated temperature was investigated. The results indicated that fine recrystallized grains preferentially grow on both sides of the bonding interface. High density dislocations accumulate around the bonding interface, providing sufficient energy for grain boundary migration. The elimination of interface line was through dynamic recrystallization (DRX) induced by the migration of interfacial grain boundaries (IGBs). The bonding interface could be hardly healed when bonding temperature at 530 °C, since continuous interfacial oxides severely impeded fine grains step over the interface. As bonding temperature increased to 560 °C, the interfacial oxides decreased and the barrier of discontinuous oxides to interface diffusion decreased. Good interface healing was achieved due to interface recrystallization and the elimination of bonding line. Bonding test results showed that the joint obtained at 560 °C possessed higher bonding strength with 318 MPa, which increased by 23.25% compared to that of 258 MPa at 530 °C, and exhibited good plastic characteristics.