RSM-based multi-objective optimization of process parameters for aluminum alloy pipe stir welding: mechanical and microstructural evaluation

Purpose This study aims to optimize the friction stir welding (FSW) process parameters for AA1100 aluminum alloy pipe joints and evaluate their effects on tensile strength, microhardness, and microstructural characteristics. The objective is to identify the optimal combination of tool rotational speed, welding speed, and axial load for achieving superior joint performance suitable for industrial piping applications. Design/methodology/approach AA1100 aluminum alloy pipe joints were fabricated using friction stir welding. Response Surface Methodology (RSM) based on a Box-Behnken Design (BBD) was employed to investigate the influence of tool rotational speed, welding speed, and axial load on the mechanical properties of the welded joints. Analysis of Variance (ANOVA) was used to evaluate the significance of process parameters and their interactions. Multi-response optimization was performed using the desirability function approach to simultaneously maximize tensile strength and microhardness. Microstructural characterization was conducted to examine grain refinement and weld quality in the stir zone. Findings The ANOVA results indicated that tool rotational speed was the most influential process parameter for both tensile strength and microhardness. The quadratic models exhibited high coefficients of determination (Rˆ2 = 0.99 for tensile strength and Rˆ2 = 0.98 for microhardness), although significant lack of fit was observed for both responses. Multi-response desirability optimization predicted an optimum at 1100.24 rpm, 42.21 mm/min and 4.39 kN, with predicted tensile strength and microhardness of 116.001 MPa and 47.8767 HV, respectively, and an overall desirability of 0.979. Confirmation experiments at the nearest practically achievable settings of 1100 rpm, 42 mm/min and 4.5 kN produced responses within ±10% of the corresponding model predictions. Practical implications The optimized welding parameters obtained in this study can be utilized for the production of high-quality AA1100 aluminum pipe joints in lightweight structural, chemical processing, and industrial piping applications. The proposed optimization methodology can also be extended to other aluminum alloy welding applications to improve joint performance and process efficiency. Originality/value This study presents a comprehensive investigation of friction stir welding of AA1100 aluminum alloy pipe joints using an integrated RSM-based multi-objective optimization approach. The combined assessment of tensile strength, microhardness, and microstructural characteristics provides valuable insights into process optimization and contributes to the development of reliable high-performance welded aluminum pipe structures.