Welding of aluminum alloy to zinc coated steel by cold metal transfer

Introducing the aluminum alloy into the steel body structure allows the reduction in the vehicle weight and improves the fuel efficiency. However, it is a still great challenge to weld aluminum alloy to steel due to their differences in the physical, mechanical and metallurgical properties. In this study, aluminum alloy 6061-T6 was welded with zinc coated low carbon steel by cold metal transfer (CMT). Effects of the pre-setting gap at the interface of aluminum alloy sheet and steel sheet as well as the offset distance of the electrode torch from the aluminum alloy sheet edge on the weld qualities were investigated. The tensile shear tests were carried out to evaluate the mechanical property of the welds. In addition, optical micrograph, scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS) were used to analyze the weld microstructure. Experimental results indicated that the intermetallic layer thickness in the CMT welds was well controlled below the 10 μm, which facilitates the achievement of relatively high weld strength. Furthermore, a pre-setting gap and an appropriate post-weld heat treatment can improve the weld strength. However, the weld strength was decreased by increasing the offset distance of arc torch. In addition, the pre-setting gap also affects the intermetallic layer morphology. The formation of brittle Al_xFe_y could be suppressed by the presence of the remained zinc in the steel side.