Characteristics of joint and interface layer during bypasscurrent MIG welding-brazing of aluminum and steel dissimilar metals

By pass-current MIG welding-brazing was conducted with 2 mm thick 6061 aluminum alloy plates and galvanized steel plates. The microstructure and mechanical properties of lap joints were investigated by optical microscopy, scanning electron microscope with energy dispersive spectrometer and tensile testing. The effect of welding speed on interface layer and joint characteristics during by pass-current MIG welding-brazing of aluminum alloy to steel was analyzed. The results show that with the increase of welding speed, the welding heat input reduced, and the interface temperature dropped which decreased the diffusion of elements and finally reduced the thickness of interface layer. In addition, the tensile strength of joint tended to increase at first and then reduce with the increase of welding speed, and reached a maximum of 135.32 MPa. When the welding speed was low, the high interface temperature increased the possibility of forming brittle intermetallic compounds which would reduce the performance of the resultant joint. On the contrary, defects such as incomplete brazing and pores in the interface because of insufficient reaction could occur at higher welding speed.