Effect of Rotation Speed on Intermetallic Compounds and Failure Load of RFSSW-ed Dissimilar Al/Mg

In this work, refill friction stir spot welding (RFSSW) was used to join 5083 Al and AZ31. The effect of rotation speed on joint formation, intermetallic compounds (IMCs), and failure load of the welded joints was mainly studied. The results showed that dissimilar Al/Mg alloys could be successfully joined by RFSSW, and defect-free joints were obtained at rotation speed of 2400 rpm, welding time of 2 s, and sleeve plunge depth of 2.2 mm. The mechanical stirring induced by the rotation of the sleeve caused the formation of liquid eutectic phase during welding. Upon cooling, the liquid eutectic phase resulted into IMC. Thicker IMC was formed in the joint center and at higher rotation speed. The joint failure load firstly increased and then decreased by increasing the rotation speed. The maximum value of 3.6 kN was obtained at the rotation speed of 2400 rpm. The XRD results showed that IMCs of Al₃Mg₂ and Al₁₂Mg₁₇ were formed inside the joint.