Effect of Al-Cu Alloy Sheet on Microstructure and Properties of Steel/Aluminum Dissimilar Metal Laser-MIG Hybrid Welded Joint

The dissimilar metal welding of Q890 steel/6063 aluminum alloy was carried out by laser-MIG hybrid welding process controlled by PLC system. The effect of the addition of Al-Cu alloy sheet to the steel side groove surface on the microstructure, hardness and tensile properties of the joint was studied. The results show that the laser-MIG hybrid welded joint had typical brazing characteristics. The interface layer of the joint without Al-Cu alloy sheets was composed of tongue-like Fe₂Al₅ phase and coarse needle-like Fe₄Al₁₃ phase with a thickness of about 18 μm. The interface layer with Al-Cu alloy sheet was composed of tongue-like (Fe,Cu)₂Al₅ phase and fine flocculent (Fe,Cu)₄Al₁₃ phase with a thickness of about 9 μm, and the microstructures of weld zone and the heat-affected zone were similiar with those without Al-Cu alloy sheet. The hardness of the interface layer of the joint with Al-Cu alloy sheet was about 59 HV lower than that without Al-Cu alloy sheet. The tensile strength of the joint with Al-Cu alloy sheet was 109.8% higher than that without Al-Cu alloy sheet; the fracture location of joints with and without Al-Cu alloy sheet both occurred in the interface layer.