Friction stir welding parameter optimization for dissimilar AA2014 and AA5052 aluminium alloys

This scientific research has optimized the parameters of Friction Stir Welding (FSW) for dissimilar aluminium alloys of AA2014 and AA5052 by using Response Surface Methodology (RSM) with a Box-Behnken Design (BBD). Four critical processing variables, i.e., tool rotating speed (1500-2100 rpm), pin geometry (triangle, circular, square), axial load (7-10 kN), and welding speed (10-20 mm/min), were systematically varied to assess their influence on ultimate tensile strength (UTS), yield strength (YS), elongation (E), and microhardness (H). Multi-response optimization using the desirability function revealed a set of favourable conditions: 1879.95 rpm, square pin, 10 kN axial load, and 17.62 mm/min welding speed. Under these conditions the mechanical performance of the weld showed a balance of UTS = 257.76 MPa, YS = 196.96 MPa, E = 4.41%, and H = 100.96 Hv with a combined desirability of 0.880. Subsequent validation experiments proved the model to be reliable, with errors in the prediction of UTS and YS less than 1.5%. Microstructural examination showed that the optimized weld had a fine equiaxed grain structure and a homogeneous distribution of Al₂CuMg precipitates in the stir zone that is due to complete dynamic recrystallization and thorough material mixing. On the contrary, coarse grains, clusters of precipitates, and tunnel defects were produced by sub-optimal parameters, which correlated with inferior mechanical properties. In this research, the integrated approach of RSM-BBD-desirability approach has been shown to be effective in the optimization of FSW of this dissimilar pair of alloys to produce defect-free joints with an improved strength-hardness balance suitable for lightweight structural applications.