Influence of Friction Stir Welding Parameters and TiB₂ Content on Tensile Properties and Weld Nugget Hardness of AA7075 Composites: Taguchi L27 Optimization

Abstract

This study investigates the addition of friction stir welding (FSW) process parameters on mechanical characteristics of AA7075 aluminium matrix composites reinforced by titanium diboride (TiB₂) particles. AA7075/TiB₂ composites with 3, 6, and 9 wt.% reinforcement was fabricated by stir-casting technique and subsequently joined through FSW. A Taguchi L27 orthogonal array was employed to evaluate four independent factors: welding speed (30–70 mm/min), tool rotational speed (900–1300 rpm), TiB₂ reinforcement content (3–9 wt.%) and axial load (3–7 kN). Percentage elongation (PE), Ultimate tensile strength (UTS) and weld nugget hardness (WNH) were considered as the mechanical responses. Taguchi signal-to-noise (S/N) ratio analysis and analysis of variance (ANOVA) were performed to determine parameter significance and identify the preferred welding conditions. ANOVA showed tool rotational speed were dominant factor affecting UTS (60.87%) and PE (43.27%), whereas TiB₂ content contributed most significantly to WNH (73.83%). The fitted models achieved coefficients of determination (R²) of 98.26%, 96.61%, and 97.97% for UTS, PE, and WNH, respectively. The preferred conditions for maximizing UTS were 1100 rpm, 50 mm/min, 5 kN, and 6 wt.% TiB₂, yielding a predicted strength of 497.38 MPa. Maximum predicted PE (8.21%) was obtained at 1100 rpm, 50 mm/min, 5 kN, and 3 wt.% TiB₂, while the highest predicted WNH (193.03 HV) corresponded to 1100 rpm, 50 mm/min, 7 kN, and 9 wt.% TiB₂. The findings demonstrate that the preferred axial load and reinforcement concentration depend on the mechanical response, highlighting the effectiveness of Taguchi-based optimization for selecting FSW conditions in AA7075/TiB₂ composites.