Influence of process parameters on joint characteristics in friction stir welding of Al/Cu dissimilar materials for lithium-ion battery

The aluminum to copper dissimilar joining has great interest to industrial fields of lithium-ion battery, such as lead tab and busbar materials as a lap joint configuration. In this study, the dissimilar lap joining of the 1050 Al alloy with thickness of 0.5 mm and commercial pure copper with thickness of 1.0 mm has been carried out by friction stir welding (FSW) with three different rotation speeds (400, 500, and 600 rpm) and three different travel speeds (60, 120, and 180 mm/min). The influence of process parameters on Al-Cu dissimilar joint characteristics was investigated. From the results, a defect-free joint was achieved under the condition of rotation speed of 600 rpm and travel speed of 60 mm/min with a tensile-shear load of 913 N for the joint. In contrast, when the rotation speed is 400 rpm, the tensile-shear load reached only 646 N, where void and tunnel defects were observed, which results indicated that a higher heat input contributed to a higher tensile-shear load due to sufficient plasticization. The minimum hardness value in the TMAZ was 31 HV at a rotation speed of 600 rpm, which is a 36% decrease compared to the Al base material; this thermal softening is caused by low dislocation density. The intermetallic compounds formed in joints were Cu9Al4 and CuAl2 with a layer thickness of 0.64 mu m. According to the Al-Cu joint electrical resistance test, the minimum electrical resistance value was about 70 mu omega, which corresponded to the condition with the maximum tensile shear load. It can be inferred that the defect-free welded joint and sufficient joining area are crucial factors for ensuring smooth current flow compared to the thickness of the IMC layer in solid-state process.