Abstract: 2 mm-thick 6061-T6 aluminum alloy and SPCC cold-rolled steel plate are used to obtain aluminum steel composite joints with both fusion and brazing characteristics by means of wire filling laser brazing method. The influences of pre-coated flux, groove bevel angle, bevel morphology and solder composition on the microstructure and mechanical properties of brazing joint are studied. The results show that pre-coating flux can greatly improve wettability of filler metal. The mechanical properties of laser brazing joint are better when 60° groove is prefabricated on the side of steel base metal than when 45° groove is prefabricated.. When the prefabricate groove angle of steel material is 60°, and the laser power, welding speed, wire feeding speed, laser defocusing amount, offset center of the laser spot center are 3.1 kW, 0.5 m/min, 2 m/min, ?8 mm, +0.6 mm, respectively, with ER2319 Al-Cu filler metal, the average and maximum tensile strength of the joint are respectively 147 MPa and 159 MPa, the interface layer presents short whisker shape, the interface layer is 5-8 μm in thickness, the Cu element is dissolved in Al-Fe brittle phase by replacing Fe elements to reduce its brittleness. With ER5356 Al-Mg filler metal, the average tensile strength of the joint is 118 MPa when the laser power is 3 kW, the interface layer presents coarse saw tooth shape, and consists of FeAl2, Fe₂Al₅ and FeAl₃ phase, the interface layer is 8-12 μm in thickness, the Mg element is gathered at the outside of brittle phase, and it has no obvious inhibitory effect on the growth of Al-Fe brittle phase; with ER4043 Al-Si filler metal, the average tensile strength of the joint is 129 MPa when the laser power is 3 kW, the interface layer presents small saw tooth shape, the interface layer is 3-4.5 μm in thickness, the Si element is dissolved in Al-Fe brittle phase to inhibit its growth.

Key words: aluminum-steel joint, laser welding-brazing, pre-coated flux, interface structure, mechanical property