Spot welding between Al alloy and some kinds of steels by friction stirring was conducted. In the process, a rotating tool was plunged into the Al alloy which was overlapped onto the steel plate, and held at the plunge depth for a few seconds with rotating condition. In this welding, friction stirring was adopted only inside of the Al alloy, and welding between Al alloy and steel is performed by an interaction of stirred Al alloy to the fixed steel surface. Mechanical strength of the joints was evaluated by both tensile shear test and cross tensile test. From the observation results on the microstructure of the weld interface, it was found that Fe/Al intermetallic compound with a few m thickness was formed at the interface. It was found that Zinc coated layer intrinsically has a role to protect the steel materials at a static condition, however, in the stirring condition of Al alloy, Zinc layer easily moved toward the outside of stirring zone and resultant fresh surface of the steel enables formation of the higher mechanical strength of the joint.
