This paper describes the joining phenomena and the tensile strength of friction welded joint between type 1070 pure aluminum (CP-Al) and oxygen free copper (OFC). When the joint was made at a friction pressure of 30 MPa with a friction speed of 27.5 s −1 , the upsetting (deformation) occurred at the CP-Al side. When the joint was made at a friction time of 2.0 s, the whole weld interface on the OFC side had the transferred CP-Al, and it was obtained approximately 30% joint efficiency. Then, the joint efficiency increased with increasing friction time, and it was obtained approximately 63% joint efficiency at a friction time of 12.0 s. The joint fractured at the weld interface, which had a CP-Al adhering to the weld interface on the OFC side. When the joint was made with friction times of 2.0 s and 6.0 s, the joint efficiency increased with increasing forge pressure and then the joint was obtained the CPAl side fracture at a forge pressure of 135 MPa or higher. However, the joint did not achieve 100% joint efficiency because the adjacent region of the weld interface at the CP-Al side was softened. In addition, the joint at a friction time of 2.0 s had no intermetallic compound (IMC) layer at the weld interface although the not-joined region was slightly observed. On the other hand, the joint at a friction time of 6.0 s did not have the not-joined region at the weld interface although the IMC layer was slightly observed. In conclusion, to obtain higher joint efficiency with fracture on the CP-Al side, the joint should be made with higher forge pressure, and with the suitable friction time at which the entire weld interface of the OFC side had the transferred CP-Al. IntroductionBecause an expansion in the use of dissimilar metal joints (referred to as dissimilar joints) is expected and widely used in various component parts, easily welding method for dissimilar metal joints is required. On the other hand, dissimilar welding operations have several severe problems in industrial usage. One problem will occur when the dissimilar joints are welded by using fusion welding processes which conventionally produce intermediate layer (interlayer) consisting of brittle intermetallic compound (IMC) at the joint interface of both base metals to be joined. The interlayers usually give detrimental damages on mechanical and metallurgical properties of dissimilar joints (For example, American Welding Society, 1982). In particular, fusion welded joints between aluminum or its alloys (referred to as the Al-system material) and copper or its alloys (referred to as the Cu-system material) have also some problems, e.g. the generation of blowholes and cracks at the joint interface (For example, Mizuno et al., 1999). Therefore, a welding process is urgently required, which will reduce the degradation of the mechanical and metallurgical properties of the joints between Al-system material and Cu-system material. 1

This paper described the tensile strength of friction welded joint between Al-Mg alloy (JIS A5052) and pure copper (OFC). In particular, the joining phenomena during the friction process and the effects of friction welding condition such as friction pressure, friction time and forge pressure on the joint strength have been investigated, and the metallurgical characteristics of joints have been also observed and analyzed. The adjacent region of the weld interface at the A5052 side was upset during the friction process, although that of the OFC side was hardly upset. When the joint was made with a friction pressure of 30 MPa, all joints fractured at the weld interface because those joints had the not-joined region at this portion. To reduce the not-joined region, the joint was made with increasing forge pressure. All joints did not have a joint efficiency of 100% (same tensile strength as the A5052 base metal) and the fracture on the A5052 base metal without crack at the weld interface, although the joint efficiency increased with increasing forge pressure. It was showed that the joint had the mechanically mixed layer as the lamellar structures of A5052 and OFC on the adjacent region of the weld interface at the A5052 side, and that layer influenced to the fractured point of the joint. The mechanically mixed layer decreased with decreasing friction time and with decreasing friction pressure after the initial peak. Then, the joint, which had the same tensile strength as the A5052 base metal, the fracture on the A5052 base metal with no crack at the weld interface, and less mechanically mixed layer with no the intermetallic compound (IMC) interlayer on the weld interface, could be successfully achieved. In conclusion, it was suggested that the joint should be made with a low friction pressures such as 20 MPa to prevent generating of the mechanically mixed layer, an opportune friction time such as 6.0 s without generating the IMC interlayer, and a high forge pressure such as 240 MPa in order to achieve completely joining of the weld interface and the fracture on the A5052 base metal.

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