Effects of heat input on wettability, interface microstructure and properties of Al/steel butt joint in laser-metal inert-gas hybrid welding-brazing

Laser-metal inert gas (MIG) hybrid welding-brazing was adopted to achieve a dissimilar metal butt joint of 6061-T6 aluminum alloy and 304 stainless steel. The effect that laser power and welding speed had upon the wett-ability, intermetallic compound (IMC) layer microstructure and tensile strength of the joint with and without reinforcement was investigated. The results show that the spreading width of the molten metals on both sides of the steel increased with welding heat input, where the maximum spreading width on both sides of the steel was 5.7 and 4.8 mm respectively for a welding speed of 5 mm/s and a laser power of 1000 W. The total thickness of the IMC layer increased and its morphology varied with increasing heat input. The maximum tensile strength of the joint without reinforcement was improved to 180 MPa with a welding speed of 5 mm/s and a laser power of 1000 W, which was attributed to the fact that the transformation of Fe4Al13 morphology reduced the stress concentration in this layer. The tensile strength of the joint with reinforcement was up to 200 MPa (70% of the 6061-T6 tensile strength). The fracture occurred at the heat-affected zone of the 6061-T6 aluminum alloy.