Abstract
SPCC steel to 6061-T6 aluminum alloy were lap welded by friction stir welding using a numerical fiction stir welder. The rotational tool with a probe of 1.1mm in length was inserted to A6061 sheet such as upper sheet. A thin compound layer was formed at the weld interface between SPCC and A6061. And microstructure of stir zone showed fine grain structure than that of the base metal. The hardness of stir zone and heat affected zone of A6061 side were softened than the base metal. Maximum tensile shear load of joint showed 6.2kN.