Effect of Mg and Si on intermetallic formation and fracture behavior of pure aluminum-galvanized carbon-steel joints made by weld-brazing

Commercial pure aluminum and galvanized carbon steel were lap-welded using the weld-brazing (WB) technique. Three types of aluminum filler materials (4043, 4047, and 5356) were used for WB. The joint strength and intermetallic compounds at the interface of three series of samples were analyzed and compared. Depending on the Si content, a variety of ternary Al-Fe-Si intermetallic compounds (IMCs) such as Fe4(Al,Si)13, Fe2Al8Si(τ5) , and Fe2Al9Si2 (τ6) were formed at the interface. Mg element in 5356 filler material cannot contribute to the formation of Al-Fe intermetallic phases due to the positive mixing enthalpy of Mg-Fe. The presence of Mg enhances the hot cracking phenomenon near the Al-Fe intermetallic compound at the interface. Zn coating does not participate in intermetallic formation due to its evaporation during WB. It was concluded that the softening of the base metal in the heat-affected zone rather than the IMCs determines the joint efficiency.