The Mechanism and Evolution of Interface by Introducing Multi-Directional Stresses for 5A90 Al-Li Alloy Diffusion Bonding

Currently, the 5A90 Al-Li alloy has been regarded as the most competitive lightweight structural material across various industries, particularly in the aerospace domain. Nevertheless, its diffusion bonding remains an urgent issue to be addressed in industrial applications. In this research, deformation was induced by introducing multi-directional stress, leveraging the distinct plastic characteristics of the Al₂O₃ oxide layer on the surface of the aluminum alloy and the 5A90 plate. The brittle nature of the Al₂O₃ oxide layer formed on the aluminum alloy surface causes it to fracture under stress, thereby exposing a new surface for diffusion bonding. Evidently, the introduction of deformation effectively mitigates defects such as pores and cracks at the diffusion bonding interface and significantly reduces the oxygen element content. The potential phases at the diffusion bonding interface are Al, MgO, and Al₃Mg₂. EBSD microscopic observations reveal that the dislocation density within the recrystallized grains is extremely low, and the lattice integrity is high, indicating a typical state of complete recrystallization. The subgrain boundaries gradually transform from low-angle to high-angle grain boundaries, and the formation of subgrain boundaries due to strain promotes the evolution of new grain boundaries along the original grain boundaries.