抄録
Dissimilar friction stir spot welds between aluminum and magnesium alloys were fabricated using a tool without probe. The tool had a scroll groove on its shoulder surface to induce material flow in the nugget. The tensile strengths of dissimilar welds were comparable to those of the magnesium similar welds made by the same tool. Thin intermetallic compound layer of Al_<12>Mg_<17> was formed along the interface between aluminum and magnesium sheets. EDX analysis revealed that the thickness of intermetallic compound layer was dependent on the distance from the center of nugget, where the thickness increased near the edge of the tool due to the upward material flow in the nugget. The intermetallic compound layer resulted in the bonding between the dissimilar alloys. Subsequently, fatigue tests were 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 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 intermetallic compound layer at the higher load levels.
