Sustainable assessment of process–reinforcement interaction effects on mechanical strength of FSW Al 7475 hybrid composites

This paper focused to enhance the mechanical and microstructural properties of Al 7475 alloy by incorporating Si₃N₄/TiO2 hybrid ceramic particles in developing composites through Friction Stir Welding (FSW). Tool rotational speed (TR), Plunging Force (PF), Travel Speed (TS) and Si₃N₄/TiO2 ratio (RE) were found to be the four key process parameters. The UTS and BHN of Al 7475 surface composite improved significantly, due to the very fine grains and the enhanced interfacial adhesion between Si₃N₄/TiO₂ (RE). The SEM analysis of the fracture surface showed a uniform distribution of fine and deep dimples, indicating that a ductile mode fracture along with high-level metallurgical interaction with minimal void formation. Analysis of variance (ANOVA) results showed that the Si₃N₄/TiO₂ was highly significant on UTS, with also significant interactive (TR*RE, PF*RE) and quadratic effects (TR², RE²). The composite desirability function (CDF) and Response Surface Methodology with Box-Behnken design (RSM–BBD) optimization was observed between predicted and experimental values. The optimal UTS of 512.36 MPa and hardness of 142.76 Hv was obtained by CDF, whereas the RSM–BBD achieved a slightly higher UTS of 517.95 MPa and hardness of 138.41 Hv. Overall, the developed FSW-based hybrid reinforcing technique is an environmentally friendly, energy-saving and low-cost approach for manufacturing high-performance aluminium surface composites. This concept can be simply adapted for aerospace, automotive and defence industry to enhance the service life of the component, decrease material wastage and enhance mechanical reliability in high operating conditions.