Koichi Kaizu

In a previous study, the tensile strength of dissimilar friction welded joints that was composed between commercially pure Al (AA1070) and low carbon steel (LCS) decreased with increasing forge pressure. This result was not applicable to the general consequence of friction welding. To prevent a decrease in the tensile strength of joints by the increase in forge pressure, the improving method of tensile strength in friction welding was investigated. Two types of AA1070 with different tensile properties due to tempering condition were used, and the weld faying part of the specimen had various overhang lengths and weld diameters. Dissimilar friction welded joints, which were composed with those AA1070 side specimens and LCS specimens, were made with various forge pressures. Then, the relationship between the tensile strength of the joints and the forge pressure was evaluated. The tensile property of AA1070 base metals with various compression stresses was also investigated, and the result was compared with the tensile strength of joints. The decrease in the tensile strength of the friction welded joints with added high forge pressure, which had an AA1070 base metal fracture, could be prevented by changing of the shape at the weld faying part of the specimen and tempering condition of the AA1070 side. However, such a joint should be made with a suitable forge pressure with the AA1070 side fracture and the same tensile strength as that of its base metal since the consideration of the decrease in the tensile strength of joints by greater forge pressure can be ignored.

The joint strength and its improvement of AA5083 Al alloy joints fabricated by friction stud welding method were investigated. The diameter of the work and stud side specimens were 32.0 mm and 12.8 mm, respectively, and those were friction welded. The appropriate welding condition for obtaining high tensile strength was established as follows: a friction speed of 17.5 s−1, a friction pressure of 80 MPa, a friction time of 1.6 s, and a forge pressure of 360 MPa. However, all joints fractured between the initial weld interface and the work or stud sides, i.e. the fracture did not occur in the base metal. It could be considered that the initial oxide film on the weld faying surface of the work side was not exhausted as the flash during the welding process. To obtain the joint having the fracture in the base metal, the suitable shape at the weld faying portion of the work side specimen was suggested as the groove shape. The inner diameter of the groove corresponded to the same diameter of the stud side, and that had a groove width of 3.0 mm with a groove depth of 1.0 mm. As a conclusion, AA5083 friction stud welded joint, which had the tensile strength of the base metal and the fracture in the base metal, could make with the appropriate welding condition. Furthermore, the weld faying portion at the work side should be in the suitable shape that urges the extrusion of the flash from this side.