Influence of laser power on interfacial microstructure and mechanical properties of laser welded-brazed Al/steel dissimilar butted joint

Laser welding-brazing 2-mm-thick 6061-T6 aluminum alloy to DP590 dual phase steel in butted configuration was performed with AlSi12 filler metal. The influence of laser power on weld appearance, interfacial microstructure and tensile strength was studied. Thermal cycle at brazing interface was calculated by numerical simulation in order to clarify the interfacial reaction mechanism. A sound weld appearance and cross section could be obtained under laser powers of 2200 W and 2500 W. When the laser power was 1800 W, the interfacial intermetallic compound (IMC) was continuous thin 2-μm-thick τ₅ phase while no reaction layer was detected at the bottom of groove at the brazing interface. When the laser power was 2200 W, the interfacial IMC consisted of needle-shaped θ phase+serration-shaped τ₅ phase with average thickness of 5.2 μm. With the further increase of laser power to 2500 W, the interfacial IMC was composed of planar η phase, needle-shaped θ phase and serration-shaped τ₅ phase with average thickness of 12 μm. When the laser power increased to 3000 W, the interfacial IMC components were composed of thick planar η phase, θ phase and τ₅ phase with average thickness of 30 μm. Highest tensile strength with 140 MPa was obtained when the laser power was 2200 W. The interfacial reaction mechanism under different laser powers and relationship between IMC components and tensile strength was clarified.