Microstructural evolution and predictive mechanical modeling of B 4 C-reinforced nugget zones in friction stir welded AA6061–AA6063 dissimilar joints

Increased demand of high-strength, low-weight components in aerospace and automobile sectors has strengthened the focus on joining dissimilar aluminum alloys. Friction stir welding (FSW) is a solid-state process overcomes the thermal defects inherent in fusion welding. Nevertheless, FSW joints involving dissimilar materials tend to experience poor mechanical properties because of limited material flow. In the current research work, the mechanical strength of similar and dissimilar AA6061–AA6063 friction stir lap welds was improved by including B₄C particles within the nugget region. Experimental process parameters were tool tilt angle (TTA), traverse speed (TS), and rotational speed (RS) for optimization based on response surface methodology using central composite design (CCD). Twenty experimentation trials were followed by regression analysis modeling and statistical ANOVA testing. Optimized parameters (RS: 1106.3 rpm, TS: 31.26 mm/min, TTA: 1.526°) achieved a maximum UTS of 281.17 MPa. X-ray diffraction analysis (JCPDS: 04-0787 for α-Al, 35-0798 for boron carbide (B₄C)) ensured the retention of B₄C without unwanted phase formation. Grain refinement and distribution of particles homogeneously were observed through microstructural and scanning electron microscope analysis. This work proves that controlled reinforcement with optimized FSW parameters can noticeably enhance joint strength, providing an effective pathway toward advanced structural applications.