Modeling and parametric optimization of friction stir welding of aluminium alloy AA7068-T6 using response surface methodology and desirability function analysis

Abstract

In this investigation, high specific strength precipitation hardenable alloy AA7068-T6 was joined using friction stir welding. Experiments were carried out using the three factor-three level central composite face-centered design of response surface methodology. Regression models were developed to assess the influence of tool rotational speed, welding speed, and axial force on ultimate tensile strength and elongation of the fabricated joints. The validity of the developed models was tested using the analysis of variance (ANOVA), actual and adjusted values of the regression coefficients, and experimental trials. The analysis of the developed models together with microstructural studies of typical cases showed that the tool rotational speed and welding speed have a significant interaction effect on the tensile strength and elongation of the joints. However, the axial force has a relatively low interaction effect with tool rotational speed and welding speed on the strength and elongation of the joints. The process variables were optimized using the desirability function analysis. The optimized values of joint tensile strength and elongation – 516 MPa and 21.57%, respectively were obtained at a tool rotational speed of 1218 rpm, welding speed of 47 mm/ min, and an axial force of 5.3 kN.