Optimization of friction stir spot welding process parameters to achieve maximum failure load

Friction stir spot welding (FSSW) process is one of the friction stir welding (FSW) processes which is used for spot joining of thin sheets with different materials without melting of base metals. Box-Behnken design of response surface methodology (RSM) has been used for modelling and optimizing of parameters in different processes. The aim of this study was investigation of the effect of backplate material on the maximum failure load and failure mode in FSSW of AA7075-T6 sheets by using Box-behnken design. Three continuous parameters including rotational speed, plunge depth and plunge speed in three levels and one discrete parameter (backplate material) in two levels were considered. AA7178 and Ti6Al4V were used as backplate sheets. Continuous parameters limits were defined according to experimental tests and previous studies. The results of experimental tests were predicted by second order polynomial. According to statistical results, plunge depth, backplate material, plunge speed and rotational speed affected on the failure load respectively. Shear failure, tensile/shear failure and tensile failure mode were observed after tensile test. Maximum failure load was obtained in tensile failure mode.