Modelling and optimization of process parameters for friction stir welding of armor alloy using RSM and GRA-PCA approach

In this study, an attempt has been made to investigate the effect of shoulder flatness, shoulder diameter, transverse welding speed and pin profile on mechanical and microstructural properties of friction stir welded (FSWed) armor aluminium alloy AA7039 T6. In total 21 experiments were performed as per center composite design (CCD) approach of response surface methodology (RSM). The tensile tests were carried out to observe the ultimate tensile strength, yield strength and percentage elongation of the FSWed joints. The quadratic regression mathematical model was developed to establish a relation between inputs and outputs. ANOVA was used to ensure the significance of the process parameters and their interactions. Optimized combination of process parameters was determined using grey relation coupled with principal component analysis, a hybrid approach. The results reveal that the process parameters considered for study have a significant effect on the variation of the studied responses. The optimum values of shoulder diameter, shoulder flatness, pin profile and welding speed were found as 18 mm, 2 mm, square and 30 mm min⁻¹, respectively. The microstructural variation across different subzones of welded joint was examined to confirm the relation obtained between process variables and tensile properties. Fractographic examination of tensile specimens and microstructural examination of joints revealed that shoulder flatness with concavity and pin pulsating effect has helped in proper mixing of material and evenly distribution of secondary phase precipitates which has imparted good mechanical properties to the FSWed joint. (paper)