Modeling and Optimization of the Yield Strength and Tensile Strength of Al7075 Butt Joint Produced by FSW and SFSW Using RSM and Desirability Function Method

Friction stir welding (FSW) is introduced as a solid-state welding process. Despite the many benefits of the FSW, the effects of the thermal cycles in this process are causing softening of the joint. This phenomenon generally occurs in heat-treatable aluminum alloys and results in reduced mechanical properties of the joint. To solve this limitation, submerged friction stir welding (SFSW) has been developed which is suitable for welding of heat-sensitive alloys. In this study, 31 butt joints were first produced from Al7075-T6 using the FSW. For this purpose, the response surface methodology was selected as the design of experiments method, and the variables: tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were determined as the input variables. Then, the statistical analysis of the parameters affecting the yield strength and tensile strength of the joints was investigated. Then, 10 joints were produced using the SFSW based on the optimal values of the tool feed rate and tool tilt angle. Results of the ANOVA and regression analysis of the experimental data confirmed the accuracy and precision of regression equations and showed that the linear, interactional and quadratic terms of tool shoulder diameter and tool rotational speed effect on the yield strength and ultimate tensile strength of submerged joints. Also, the optimal conditions of input variables were determined by the desirability method and confirmed by the verification test.