In an attempt to optimize the friction spot joining process of Al alloys for automobiles (Al 5000 and Al 6000 series, thickness 1mm), effects of joining parameters such as tool rotating speed, plunging depth and dwelling time on the weld joints properties were evaluated. Experimental tests were carried out for lap joined Al plates. A wide range of joining conditions could be applied to join Al alloys for automobiles without defects in the weld zone except for certain welding conditions with an insufficient heat input. The microstructures and hardness variations in the weld regions are discussed. The microstructures of welds, corresponding to the pin hole, have dynamic-recrystallized grain similar to stir zone in FSW weld. In hardness distribution, minimum hardness region was located about 6-mm away from the weld center, corresponding to the shoulder radius of the tool. For each weld the results from tensile-shear tests are also presented. For sound joints without defects, tensile shear strength of weld joints was higher approximately 230% than acceptable criteria of tensile shear strength of electrical resistance spot-welded joints for aluminum (MIL-W-6858D).