Novel spot friction stir welding of 6061 and 5052 Al alloys

A novel two-step spot friction stir welding (FSW) technique was developed with the purpose to improve the mechanical property of the joints by removing the keyhole. In the first step, a conventional spot FSW is conducted above a round dent previously made on the back plate. Therefore, a protuberance was formed on the back side of the joints due to the flow of the materials into the dent during the welding process. In the second step, the welding process was conducted on a smooth back plate using a rotating tool without the probe in order to remove the protuberance on the back side and the keyhole on the front side. This novel spot FSW method was applied to 6061 and 5052 Al alloys, and it reveals that the final joints have a smooth surface with no defects inside and shows improved mechanical properties.