Cold metal transfer spot welding of 1 mm thick AA6061-T6

In order to meet the upcoming regulations on greenhouse gas emissions, aluminum use in the automotive industry is increasing especially in car body structure and closure applications. To address the shift from steel to aluminum, there needs to be a corresponding shift of joining technologies which consequently drives the development of an effective single sided joining process for aluminum alloys. In this paper, a variant of gas metal arc welding, i.e. cold metal transfer, CMT, which is unique in its approach to reduce the overall heat input, has been introduced to address that concern. Three welding arc modes: Standard, Pulsed and CMT are investigated to identify the advantages of CMT mode and the CMT mode was further investigated by four CMT spot welding modes: direct welding (DW) mode, plug welding (PW) mode, direct welding on a chill block (DWB) mode and plug welding on a chill block (PWB) mode. The resultant welds were investigated by macro and micro metallographic examination, microhardness testing and mechanical property testing. The results showed that the CMT arc mode could obtain the strongest welds understandably with the fewest welding defects. Under CMT arc mode, the direct welding with chill block mode (DWB) produced the largest weld faying interface. These welds also exhibited fewest partial tearing defects which led to the highest strength and ductility among the four welding modes for single sided spot welding of 1 mm + 1 mm AA6061-T6 sheet combination.