Microstructure of Aluminum/Copper Lap Joint by Friction Stir Welding and Its Performance

Abstract

An investigation has been made of the feasibility of friction stir welding of dissimilar lap joint of an aluminum plate to a copper plate, which is difficult to weld by fusion welding methods because of the formation of brittle intermetalic compounds (IMC). The joint strength depended strongly on the depth of the pin tip relative to the copper surface; when the pin did not penetrate to the copper surface the joints showed very weak fracture loads, whereas slight penetration of the pin tip to the copper surface increased the joint strength significantly. Although the level of bond strength was quite low, it exhibited a general tendency to increase with a rise in the rotation speed. Various microstructures with different morphologies and properties were observed in the stirred zone of aluminum and Al/Cu interfacial region. Comparison of the fracture location with the microstructure suggests that IMC formed in the interfacial region was responsible for the low strength of the joints. X-ray diffraction from the fracture surfaces indicated that Al4Cu9, AlCu, and Al2Cu were main intermetallic compounds formed in the interfacial region.