Interface microstructure study of friction stir lap joint of AC4C cast aluminum alloy and zinc-coated steel

AC4C cast Al alloy and zinc-coated steel are successfully lap jointed using friction stir welding. The interface microstructure is investigated using optical microscopy, scanning electron microscopy and X-ray diffraction. The mechanical properties of the joints are evaluated using tensile test. Experimental results show that the lap joint consisted of four part structures, i.e. stir zone structure of Al alloy, new intermetallic compounds layer, old intermetallic compounds layer of original zinc coat and base material of steel. The thickness of intermetallic compounds layer increases with decreasing welding speeds and has a significant effect on the strengths of the joints. Heavy thickness of intermetallic compounds layer seriously deteriorates the mechanical properties of the joints. The intermetallic compounds layer mainly contains Fe2Al5 and Fe4Al13.