Empirical modeling for the effects of welding factors on tensile properties of bobbin tool friction stir-welded 2219-T87 aluminum alloy

For the joints of bobbin tool friction stir welding (BT-FSW), welding factors such as welding speed, tool rotation speed, and shoulder pinching gap have significant effects on the ultimate tensile strength (UTS) and tensile elongation (TE). This work developed empirical models to describe the relationships between the welding factors and the tensile properties of bobbin tool friction stir-welded 2219-T87 aluminum alloy. Based on the models, the factor effects can be analyzed quantitatively and graphically, and the UTS and TE of the joints can be predicted and optimized effectively. Firstly, experiments were carried out according to a three-factor and five-level central composite design (CCD). Secondly, empirical models were developed by fitting experimental data points. Adequacies of the models were checked by the analysis of variance (ANOVA). Thirdly, the analysis and optimization processes were conducted. Based on the expressions and plots of the developed models, the individual and interactive effects of the welding factors were investigated. By the multiple-desirability function and three-dimensional response surface methodology (RSM), the optimum welding factors were calculated from the models. The validation trial has been carried out, and the result shows that the models are adequate for predicting and optimizing the BT-FSW factor effects.