Dissimilar metal joining of aluminum alloy to galvanized steel with Al–Si, Al–Cu, Al–Si–Cu and Zn–Al filler wires

Aluminum alloy sheets were lap joined to galvanized steel sheets by gas tungsten arc welding (GTAW) with Al–5% Si, Al–12% Si, Al–6% Cu, Al–10% Si–4% Cu and Zn–15% Al filler wires. Different amounts of Si, Cu and Zn were introduced into the weld through different filler wires. The effects of alloying elements on the microstructure in the weld and tensile strength of the resultant joint were investigated. It was found that the thickness of the intermetallic compound (IMC) layer decreased and the tensile strength of the joint increased with the increase of Si content in the weld. The thickness of the IMC layer could be controlled as thin as about 2 μm and the tensile strength of the dissimilar metal joint reached 136 MPa with Al–12% Si filler wire. Al–Si–Cu filler wire could result in thinner interfacial layer than Al–Cu filler wire, and fracture during tensile testing occurred in the weld for the former filler wire but through the intermetallic compound layer for the latter one. A Zn-rich phase formed in the weld made with Zn–15% Al filler wire. Moreover, the Zn–Al filler wire also generated thick interfacial layer containing a great amount of intermetallic compounds and coarse dendrites in the weld, which led to a weak joint.