Microstructure and Mechanical Properties of Friction Stir Welded Joints between Commercially Pure Copper and Al 6351 Alloy

In the present study, the effect of tool rotational speed on microstructure and mechanical properties of friction stir welded joints between commercially pure copper and 6351 Al alloy was carried out in the range of tool rotational speeds of 300-900 rpm in steps of 150 rpm at 30 mm/minutes travel speed. Up to 450 rpm, the interface of the joints is free from intermetallics and Al₄ Cu₉ intermetallic has been observed at the stir zone. However, Al₄ Cu₉ intermetallic was observed both at the interface and the stir zone at 600 rpm. At 750 and 900 rpm tool rotational speed, the layers of AlCu, Al₂ Cu₃ and Al₄ Cu₉ intermetallics were observed at the interface and only Al₄ Cu₉ intermetallics has been observed in the stir zone. The maximum ultimate tensile strength of ~207 MPa and yield strength of ~168 MPa along with ~6.2% elongation at fracture of the joint have been obtained when processed at 450 rpm tool rotational speed.