Effects of annealing on the interfacial microstructure and mechanical properties of explosively welded AZ80 magnesium alloy and A6005C aluminium alloy

Effects of annealing on the interfacial microstructure, mechanical properties, and residual stress of the explosively welded AZ80 magnesium alloy and A6005C aluminium alloy cladding plate were investigated. By explosive welding, a thin interlayer composed by an intermetallic compound, i.e. γ-Mg₁₇Al₁₂ phase, was formed at the interface of the cladding plate. After annealing at both 373 K and 473 K, the thickness of the interlayer increased. After annealing at 473 K, the interlayer changed from a single layer of γ-Mg₁₇Al₁₂ phase to a double layer of γ-Mg₁₇Al₁₂ phase and β-Al₃Mg₂ phase, resulting in a decrease in shear strength. As a result of nanoindentation measurement at the interface, the hardness was remarkably high in the β-Al₃Mg₂ phase. It was suggested that this phase became the crack initiation site for brittle fracture and the shear strength is decreased. Measurements of the residual stress using synchrotron radiation X-rays at the interface of cladding plate revealed the tendency of the generation of tensile residual stress on AZ80 magnesium alloy side and compressive residual stress on A6005C aluminium alloy side. After annealing at 473 K, residual stress in AZ80 magnesium alloy side and A6005C aluminium alloy side changed to compressive and tensile stresses, respectively, and these stress values became smaller in both cases. On the other hand, after annealing at 373 K, compressive residual stress was observed in both AZ80 magnesium alloy side and A6005C aluminium alloy side.