Optimization of tensile strength and hardness for friction stir welded aa6063-t6 pipes using RSM based grey relational analysis and desirability function approach

Abstract Joining of aluminium alloy pipes with efficient joints is one of the critical requirements in engineering fields such as aerospace, automotive, etc. Friction stir welding, one of efficient process to join aluminium alloy materials, is now being employed to join aluminum alloy pipes. While extensive research exists on FSW of plates, the optimization of process parameters for pipe welding presents unique challenges due to circumferential geometry and complex fixturing requirements. This novel study investigates the optimization of friction stir welding process parameters for improved tensile strength and hardness in friction stir welded aluminum alloy 6063-T6 pipes. Process parameters including tool rotational speed and weld speed are optimized using Response Surface Methodology based Grey Relational Analysis. Mechanical properties such as ultimate tensile strength, yield strength, hardness, and percentage elongation are evaluated. The Response Surface Methodology is used to populate various parameter combinations as design matrix for carrying out experimentations, while Grey Relational Analysis is employed to evaluate and rank the mechanical responses. The optimal parameter combination (3000 rpm tool rotational speed, 0.35 rpm weld speed) yielded significant improvements in mechanical characteristics, as confirmed by experimental validation. The results are further confirmed by deploying desirability function and analyzing the microstructure of the weld zone. The optimized weld joint achieved an ultimate tensile strength of 126.3 MPa and a hardness of 152.1 HV, representing a joint efficiency of approximately 52% and 83% improvement over the base material hardness, respectively.