Optimisation of Friction Stir Welding Parameters for Dissimilar Aluminium Alloys AA6061-T6 and AA7075-T6: Effect of Tool Pin Profile, Rotation Speed, and Feed Rate on Joint Strength, Microhardness, and Microstructure

Abstract

Friction Stir Welding (FSW) is a solid-state joining process that avoids the melting and re-solidification defects inherent in fusion welding, making it particularly suitable for joining high-strength aluminium alloys of the 6xxx and 7xxx series that are notoriously difficult to fusion weld without porosity, hot cracking, and loss of temper properties in the heat-affected zone. This paper presents a systematic experimental investigation of FSW of dissimilar aluminium alloys AA6061-T6 and AA7075-T6 using a Taguchi L16 orthogonal array design with four parameters: tool rotation speed (600, 800, 1000, 1200, 1400 rpm), welding feed rate (40, 50, 60 mm/min), tool pin profile (cylindrical, tapered, threaded taper), and axial force (4, 5, 6 kN). Ultimate tensile strength (UTS), Vickers microhardness distribution across the weld zone, and joint efficiency relative to the weaker parent material (AA6061-T6) are evaluated for all sixteen experimental runs. Signal-to-Noise (S/N) ratio analysis, ANOVA, and main effects analysis are applied to determine the optimal parameter combination and quantify the relative influence of each parameter. ANOVA identifies tool pin profile as the dominant factor for UTS (38.4% contribution) followed by tool rotation speed (26.2%) and feed rate (22.8%). The optimal parameters are tool rotation speed 1000 rpm, feed rate 60 mm/min, threaded taper pin profile, and 5 kN axial force. Confirmation experiments at the optimal setting achieve UTS = 218 MPa and joint efficiency of 70.3% relative to AA6061-T6, with maximum nugget zone hardness of 126 HV. Microstructural analysis reveals a fine, equiaxed recrystallised grain structure in the nugget zone (average grain size 4.2 µm) produced by dynamic recrystallisation during thermomechanical deformation, compared to 28.4 µm and 12.6 µm in the AA6061-T6 and AA7075-T6 parent materials respectively.

Cite as:

P. P. Bhise. (2026). Optimisation of Friction Stir Welding Parameters for Dissimilar Aluminium Alloys AA6061-T6 and AA7075-T6: Effect of Tool Pin Profile, Rotation Speed, and Feed Rate on Joint Strength, Microhardness, and Microstructure. Research and Reviews on Experimental and Applied Mechanics, 9(2), 12–20. https://doi.org/10.5281/zenodo.21902896