Microstructures and mechanical properties of metal inert-gas arc welded joints of aluminum alloy and ultrahigh strength steel using Al-Mg and Al-Cu fillers

The dissimilar metal inert-gas arc welding of aluminum alloy and ultrahigh strength steel was studied. The weld appearance was improved when welding wire was directed toward steel groove middle. The Al-steel joints have welding-brazing characteristics and include weld zone (WZ), bond zone (BZ), and interface zone (IZ). The welds with Al-Mg and Al-Cu welding wires consist of alpha-Al and beta-Al3Mg2, and alpha-Al and Al2Cu, respectively. The IZ contains needle-like Fe4Al13 and lath-shaped Fe2Al5 layers. With increasing welding current, the interface layer thickness and joint cracking sensibility increased due to enhanced heat input and tensile stress in the joints. They were decreased effectively when using Al-Cu welding wire, as the constituent Cu could restrain the growth of interface layer and lower its hardness and brittleness. In particular, Al-Cu welding wire elevated the tensile strength of the Al-steel joints from 65 MPa for Al-Mg wire to 128 MPa.