The SSM 356 aluminum alloy formed by GISS technique, which was developed to be used in the production of automobile parts and
necessary for FSSW process, is found to be good adhesion of the lap joint. The results of all experiments were very satisfying. For
rotation speed at 380 rpm, the plug depth of 1.5 mm and the welding time of 60 sec, the maximum shear strength was 174.2 MPa,
whose Joint efficiency was 92.12 percent compared with the base metal. The values of hardness in SZ ranged lower than those in other
regions, while the hardness values in the advancing side of thermo-mechanically affected zone (AS-TMAZ) were higher than those in
other regions. The evaluation of the microstructure in SZ shows that external force and heat cause the material to become plastic
deformation resulting in the new precipitations from β-Mg2si phase to β՛՛-Mg2si homogenous phase whose particle size is smaller
around 2-7 µm. The analyzed experimental design was a general mixed-level design which had a test coefficient of R2 of 0.96 at
confidence level of 95.00%.