Joining 6 mm thick dissimilar steel/Al alloy butt joints using two keyhole laser-MIG hybrid welding processes

Laser-metal inert gas (MIG) hybrid welding has been recently suggested as a feasible process for joining of steels to Al alloys for structural applications. In the present study, keyhole laser-MIG hybrid welding and laser-MIG hybrid welding–brazing processes were performed to join 6 mm thick Q235 steels and 5083 Al alloy plates. Effects of laser-MIG hybrid process parameters on the bead appearance, weld shape, interface microstructures, and microhardness of the steel/Al alloy butt joints were investigated. Research results show that a soundly joined steel/Al alloy butt joint had been achieved by using two keyhole laser-MIG hybrid welding processes. However, two laser-MIG hybrid processes had obvious different influence on the morphology, thickness, and hardness of the intermetallic compound (IMC) layer at the interface. The IMC layers at the interface produced by keyhole laser-MIG hybrid welding were mainly composed of the Fe2Al5 and the Fe4Al13 phases, whereas a new Fe2Al8Si phase was formed at the interface of the joints produced by keyhole laser-MIG hybrid welding–brazing process with Al-Si filler wires, which led to a decrease of the microhardness from 898.8 to 620.0 HV at the interface. Therefore, it demonstrates that MIG laser-MIG hybrid welding–brazing process was of considerable improvement of the brittleness of the interface of the steel/Al alloy butt joints.