Interface microstructure and bonding mechanisms of 7050 aluminum alloy thick plates produced by vacuum roll cladding

Abstract

Vacuum roll cladding (VRC) based on friction stir welding (FSW) is applied to prepare aluminum alloy thick plates, and the effect of rolling reduction ratios (60%, 70%, 80%) on the microstructure and mechanical properties at the bonding interface of aluminum alloy clad plates are investigated. The results show that voids at the interface are gradually closed and the original interface finally disappears with the increase of rolling reduction ratios. There are 3 kinds of recrystallization mechanisms at the interface during hot rolling. The contributions to the healing of the interface are in the following order: geometric dynamic recrystallization (GDRX) > discontinuous dynamic recrystallization (DDRX) > continuous dynamic recrystallization (CDRX). At a rolling reduction ratio of 80%, GDRX characterized by the “pinch-off” of original grains mainly occurs at the interface, and no aggregation of defects and impurity elements is detected. The tensile shear strength and fracture displacement at the interface both reach the level of the matrix, which indicates that a good metallurgical bonding has been achieved at the interface. Therefore, the key to improving the interfacial healing quality is to break the interfacial oxide film and further induce recrystallization at the interface through a large rolling reduction ratio.