Friction based joining process for high strength aerospace aluminium alloy

The present study investigates the metallurgical, mechanical and corrosion behavior on 6 mm plate, friction stir welded aluminium alloy (AA) 7475-T761. The process parameters of the welding process were optimized by using Box Behnken Method with a minimum number of trials. Optical and Scanning electron microscope (SEM) were used to evaluate the microstructure of weldment in different zones. Energy Dispersive x-ray Spectroscopy (EDS) analysis was carried out to analyze the extent of microsegregation of alloying elements in the different zones of the weldment. X-Ray diffraction (XRD) analysis was carried out to evaluate the phase formation and calculate the crystallite size, microstrain and dislocation density in the stir zone and base metal. Exfoliation corrosion was performed to evaluate the corrosion behavior of the weldment in the different zones. The results illustrate the defect-free welding was obtained by a combination of rotational speed (ω) 600 RPM, traverse speed (ν) 40 mm min⁻¹ and axial force (p) 10 kN. The fine equiaxed microstructure was observed in the stir zone. EDS analysis shows the extent of Cu rich microsegregation in the stir zone. Weldment produced by the above combination of parameters exhibit 76% joint efficiency. Hardness value along the weldment reveal 26% improvement in stir zone compared to the base metal due to refined microstructure. X-Ray diffraction analysis point out the high dislocation density and strain induced in stir zone is caused by dynamic recrystallization. Corrosion study confirms the stir zone has higher resistance to corrosion compared to adjacent thermos-mechanical affected zone. (paper)