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Aluminum and magnesium alloys dissimilar friction stir spot welds had been fabricated using a tool without probe whose shoulder surface had a scroll groove with the depth of 0.5mm. The scroll groove was designed to induce material flow in the nugget of spot welds. The tensile strengths of dissimilar welds were comparable to those of the magnesium similar welds made by the same tool. Thin intermetallic compound (IMC) layer consisting of Al3Mg2 and Al12Mg17 was formed along the interface between aluminum and magnesium sheets. EDX analysis revealed that the thickness of IMC layer was dependent on the distance from the center of nugget, where the formation of thin IMC layer had resulted in the bonding between the dissimilar alloys. The tensile strengths of dissimilar welds fabricated by the different conditions were dependent on the thickness of IMC layer, and were sensitive to the thickness of IMC layer around the edge of the nugget. Subsequently, tensile shear fatigue tests had been conducted, and the fatigue strengths were nearly the same between dissimilar and magnesium similar welds. Fatigue fracture modes were dependent on the load levels, where fatigue crack propagated along the interface at the higher load levels than 1000N. However, fatigue crack initiated in the lower magnesium sheets at the edge of the nugget and propagated through thickness at the low load level of 750N. Fractographic and EDX analyses revealed that the fatigue crack mainly propagated through the thin IMC layer at the higher load levels. 1. 緒 言 近年,輸送機器分野では低燃費化や高効率化のために,構造の軽量化が強く求められており,アルミニウム(Al) 合金やマグネシウム(Mg)合金等の軽金属が多用されるようになった.そのため,Al 合金と Mg 合金の接合が 重要な課題となっている.しかし,抵抗スポット溶接などに代表される従来の溶融接合手法では,接合界面に脆 い金属間間化合物が多量に形成されるため,信頼性のある継手を得る事が難しいとされている.一方,摩擦攪拌 接合(Friction Stir Welding: FSW)や摩擦攪拌スポット接合(Friction Stir Spot Welding: FSSW)は,固相接合であ るために異種金属接合に適すると考えられており,実際に Al/鋼板(福本他, 2004),Mg/鋼板(渡辺他, 2006) 1 渦溝ツールにより作製した A6061/AZ31 異種金属 摩擦攪拌スポット接合継手の疲労挙動 植松 美彦*1,柿内 利文*1,戸崎 康成*2,麻地 剛史*3 Fatigue behavior in A6061/AZ31 dissimilar friction stir spot weld made by a scroll grooved tool Yoshihiko UEMATSU*1, Toshifumi KAKIUCHI*1, Yasunari TOZAKI*2 and Takeshi ASAJI*3 *1 Gifu Univ. Dept. of Mechanical Engineering 1-1 Yanagido, Gifu 501-1193, Japan *2 Industrial Research Institute of Gifu Prefecture 1288 Oze, Seki-shi, Gifu 501-3265, Japan *3 Howa Machinery, Ltd. 1900-1 Sukaguchi, Kiyosu-shi, Aichi 452-8601, Japan Received 6 June 2014