The dissimilar metal joints of A3003 aluminum alloy and SUS304 stainless steel were newly designed and produced by multi-run lap Friction Stir Welding (FSW) technique. The joints produced were estimated on mechanical properties such as static and fatigue strength, cross-sectional observation and hardness distribution. The interface of the joint was of a reaction layer with approximately 200 to 300 nm thickness, which was identified as Al₁₃Fe₄ and Al₅Fe₂. Furthermore, FEM analysis on the multi-run lap FSWed joints was well corresponded to the result of joints strength tests. It was confirmed that a multi-run lap FSWed joint could achieve almost the same strength as an explosive welded joint if its shape and the position, number and direction of its FSW-passes were optimized.

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For the purpose of improving the defect of conventional friction welding method, new friction welding technology has been examined. New method has an intermediate material for friction between joint specimens. In addition to the experiment, the thermal elastic-plastic stress analysis by the finite element method has been carried out to search the suitable welding conditions. In this study, square cross sectional aluminum alloy joint was investigated. The results are as follows. In this test, obtained joint effciency evaluated in the tensile test is about 90％ under remaining the solid condition for interface of the specimens. The good relationship between overhang height of the burr near the interface and the joint effciency is recognized. The higher joint effciency is obtained in more than a threshold value of the overhang height. As a result of numerical estimation in this square cross sectional joint, it is to be found that the corner of cross section has lower temperature and more tensile strength than those of the center. It makes plastic deformation of both joint specimens di‹cult to weld. That is the reason not reaching 100％ joint effciency.

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