Role of zinc coat in friction stir lap welding Al and zinc coated steel

AC4C cast Al alloy and Zn coated steel were successfully lap welded using friction stir welding technology. Full strength joints could be obtained and the joints fractured at Zn coated steel base metal side, while Al alloy and unzinced steel could not be welded in the same welding conditions. The joining mechanism and the role of Zn coat on friction stir lap welding of Al alloy and Zn coated steel were put forward. The intervention of Zn coat promoted the formation of Al-Zn low melting point eutectic structure at the interface, which significantly improved the weldability of Al and steel.