Effects of Si and Mg on mechanical properties of aluminum-steel welded-brazed joint

Dissimilar metals of 5052 aluminum alloy and galvanized steel were joined with lap joint by pulsed double electrode gas metal arc welding-brazing with ER4043 filler metal and ER5356 filler metal, respectively. The interfacial microstructures, fracture behavior and fracture morphologies of the joints were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-Ray diffraction. The results show that wetting angle of weld with Al-Mg filler metal is larger than that with Al-Si filler metal. Si atoms change the shape of intermetallic compounds and inhibit the formation of Fe₂Al₅ intermetallic compound. The results of tensile tests show that the welded joints with Al-Mg filler metal mainly fracture along the interface between the intermetallic layer and the steel, and the fracture mode of the joints is brittle fracture. The welded joints with Al-Si filler metal mainly fracture in the fusion zone of aluminum alloy, and the fracture mode of the joints mainly is ductile fracture, but has the trace of brittle fracture. Hardness of joints with Al-Si filler metal was determined, the results show that the hardness of aluminum heat affect zone is obviously lower than that of the other zone, which leads to the joints with Al-Si filler metal failure in aluminum fusion zone.