Sustainable Friction Stir Spot Joining Process for Aluminum Alloy AA 4045 Parameter Optimization and Mechanical Assessment

Abstract

This study aims to improve Friction Stir Spot Joining (FSSJ) parameters for AA4045 by examining their effects on energy use and mechanical strength. Also, it proposes a sustainable FSSJ strategy for AA4045 aluminum alloy through multi-parameter optimization and energy-based process evaluation. A Taguchi L9 experimental design was used to study how the rotational speed, plunge depth, and dwell time affect joint performance. Lap-shear tests showed that speeds between 900 and 1200 rpm with a plunge depth of 0.5 to 0.8 mm gave the best bonding. In contrast, a shallow plunge depth of 0.2 mm did not allow enough penetration, resulting in weak adhesion at the interface. Sample No. 9 (1200 rpm, 0.8 mm, 2 s) had the highest shear strength at 2.7 kN, while Sample No. 1 (600 rpm, 0.2 mm, 1 s) had the lowest. The sustainability assessment found that higher rotational speeds increased energy use from 0.06 to 0.11 MJ per weld, but 900 rpm gave the best strength-to-energy ratio. Life-Cycle Assessment (LCA) with ecoinvent data showed a Global Warming Potential (GWP) of 0.004–0.007 kg CO₂-eq per weld, confirming that FSSJ of AA4045 is a low-emission alternative to traditional spot welding. These findings show that FSSJ is an eco-efficient joining method for lightweight applications. This research offers a practical guide for using energy-efficient manufacturing in lightweight structures, which is important for reducing emissions in transport and supports SDG 9 (Industry, Innovation, and Infrastructure) and SDG 12 (Responsible Consumption and Production). Optimised parameters not only lower environmental impact but also improve joint strength.