In this research paper, an endeavour was made to devise empirical relations amidst the process parameters of friction stir welding (FSW) and tensile relevant strength of AZ80A Mg alloy joints, based on a 6 parameters—5 levels based central composite design (CCD). Mathematical equations illustrating the impact of process parameters of FSW were formulated based on quadratic regression based analysis to optimize the parameters for attaining superior tensile strength and sensitivity related equations were established from these numerical models. A detailed sensitivity characteristic relevant map for the FSW of AZ80A Mg alloys was established forecasting the fine tuning related prerequisites of the employed FSW parameters. Coefficient of determinant (R²) announced that 99.062% of the overall variability was described by the formulated model and only lower than 1% of the overall variations was not justified by the model. Predicted R² was also in perfect agreement with the adjusted R² and announced the model’s capability to demonstrate 95.43% of the variability in the generated data. Highest value of tensile relevant strength (80.77% of the parent metal) was exhibited by the AZ80A Mg alloy joint fabricated under optimized parameters. Tensile relevant strength of AZ80A Mg joints was observed to be highly sensitive to traverse speed of the employed tool.

In this work, an endeavour was made to determine the impact of the tool’s shoulder diameter, pin profile, rotational and traverse speeds on the mechanical properties of the friction stir welded namely Ti–6Al–4 V alloy joints. A total of 21 experiments were carried out based on the central composite design (CCD) concept of response surface methodology (RSM). A quadratic regression based numerical model was formulated to ascertain the relationship amidst the parameters of FSW process and the mechanical properties of the fabricated Ti alloy joints. Analysis of variance (ANOVA) was employed to confirm the importance of parameters and their interactive impacts. Optimized process parameter combinations were ascertained by grey relation based analysis (GRA) was coupled together with principal component analysis (PCA), a hybrid based approach. Single score of GRG based response was determined and GRG scores were ranked for all experiments. 1st rank was attained by the experiment no. 20 possessing a GRG score of 2.9989. Optimized values of 25 mm shoulder diameter having a taper cylindrical pin geometry employed at a tool traverse speed of 40 mm min⁻¹, rotational speed of 1400 rpm resulted in the generation of flaw free Ti alloy joint possessing a largest tensile strength of 809.8 MPa, yield strength of 778.7 MPa and percentage of elongation of 6.9%. SEM based fractography of Ti alloy joint specimens announced that taper cylindrical pin geometry along with 25 m shoulder diameter of employed tool have an inevitable part in generating frictional heat in ideal volumes and a perfect stirring action during FSW process.