Interfacial microstructure and reaction mechanism with various weld fillers on laser welding-brazing of Al/Cu lap joint

The influence of pure Al, Al-Si and Zn-Al weld fillers on microstructure and mechanical properties was investigated during lap laser welding-brazing of Al to Cu. Al_4.2Cu_3.2Zn_0.7 IMC layer and plate-like Al₂Cu phase were observed at Al/Cu interface with pure Al and Al-Si weld fillers. Microcrack was easy to generate in Al₂Cu phase decreasing the joint strength. When the Zn-Al weld filler was adopted, the formation of Al₂Cu brittle phase was limited by low Al content and the CuZn and CuZn₅ IMC layers were observed at Al/Cu interface. According to the chemical potential, the diffusivity of Cu atoms in Zn-Al weld filler was much lower than that of pure Al and Al-Si weld fillers, which prevented from the formation of coppery phases near the Al/Cu interface. Si atoms tended to concentrate at Al/Cu interface. It played a role in obstructing the diffusion of Cu atoms, enhancing the Al/Cu joint strength to some extent. According to nanoindentation result, the mechanical property of the formed phases (CuZn and CuZn₅) in the case of Zn-Al weld filler was better than that formed with pure Al and Al-Si weld fillers such as Al₂Cu and Al_4.2Cu_3.2Zn_0.7. The highest tensile strength was 148 MPa with Zn-Al weld filler.