海津 浩一

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.

A6063とFCD400の薄肉円管の接合に摩擦圧接法を用い，継手強度に及ぼす圧接条件の影響を調べた．外径 16mm，内径 12mmとし，摩擦速度27.5s-1，摩擦圧力30MPaで接合した．その結果，摩擦時間0.2s，アプセット圧力165MPaの時にA6063母材に対して継手強度が約76%の引張強度となった．そして，熱処理による脱炭処理を行ったところ，継手強度が約87%まで増加することが分かった

A5052/SUS304摩擦圧接継手に温度を種々変化させて後熱処理を施した．そして，熱処理を施した継手の引張強さを調べた．摩擦圧力30MPa，摩擦時間1.5s，アプセット圧力240MPaとして継手を作製したところ，接合したままではA5052母材に対して約95%の引張強さで圧接面から破断した．一方，熱処理温度の増加にともない継手の引張強さは減少し，475℃～500℃で急激に減少することがわかった．

溶融溶接法では接合が困難である，難燃性Mg合金のAZX611と，Al合金の代表格であるA5083を摩擦圧接法を用いて接合した．A5083側の変形を促し，継手の引張強さを向上させるために，AZX611側に設ける接合端部長さを種々変化させて摩擦圧接を行った．その結果，AZX611側の直径16mm，接合端部長さ25mmの場合，最大でAZX611母材の約65%の引張強さを有した継手を作製することができた．