Effect of Friction Stir-Welding Tool Pin Geometry on the Characteristics of Al-Cu Joints

Abstract

Friction stir welding (FSW) is considered to be a solid-state welding technique that is suitable well for joining copper and aluminium sheets. The current experimental study focused on the influence of pin geometry on the micro-structural and mechanical characteristics of such joints. An aluminium sheet was welded to a copper sheet at a constant rotational speed of 1280 rpm and a traverse speed of 16 mm/min. The welding tool was made from W302 steel with four different pin profiles: straight cylindrical, tapered, triangular, and squared. When the squared pin was utilized, the optimum joint was produced as the specimen prepared from this joint had a defectfree structure and a tensile strength of 107.2 MPa (80% of the aluminium strength). On the other hand, the pin with a triangular profile was utilized to determine the minimum characteristics, and the specimens' structures revealed dislocations, separations, and cracking in copper particles inside the aluminium matrix. The microhardness trend is consistent across all specimens. Moreover, specimens welded using squared and cylindrical pin tools have the maximum hardness values obtained at the stir zone of the copper side. The inspection of fractured surfaces showed well mixing between aluminium and copper as well as ductile fracture when a squared pin tool was used while it showed a combination of ductile fracture and brittle fracture for the specimen welded with a triangular pin tool. Based on this study, the use of the squared pin tool gives the most favourable results compared with other pin profiles.