Statistical analysis and optimization of tensile strength of Al7075 butt joint produced by friction stir welding and submerged friction stir welding via response surface methodology and desirability approach

The thermal cycles involved in friction stir welding process cause softening in the joint of heat-treatable aluminum alloys. To overcome this limitation, submerged friction stir welding process has been developed. In this study, firstly, the butt joints were produced from Al7075-T6 alloy using friction stir welding process. To this end, the response surface methodology was selected as the experiment design technique. So, the factors such as tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were identified as the input variables. Then, a statistical analysis of variables affecting the tensile strength of joints was performed. Afterward, the butt joints were produced using submerged friction stir welding process based on the optimal values of tool feed rate and tool tilt angle. The obtained results from analysis of variance and regression analysis of experimental data confirmed the accuracy of regression equations. Furthermore, it is shown that the linear, interactional and quadratic terms of the tool rotational speed and tool shoulder diameter are effective on the ultimate tensile strength of the underwater welded joints. Also, the optimal condition of input variables was determined using the desirability method. In addition, the optimal condition has been confirmed by implementing the verification test.