Multi-Response Optimization of Process Parameters of Nanocomposite AZ91D/Al ₂ O ₃ /SiC Fabricated by Friction Stir Processing

Multi-response optimization of multipass friction stir processing (MPFSP) of AZ91D magnesium alloy with Al 2 O 3 and SiC nanoparticles (NPs) was performed using response surface methodology (RSM) based on the Central Composite Design (CCD), along with metallurgical characterization. The maximum UTS of 337.41 MPa was found with 5P FSP with SiC and Al 2 O 3 NPs due to uniform dissemination of NPs in the processed zone, which acted as barriers to dislocation motion, enhancing tensile properties. This improvement was attributed to several factors, including microstructural modifications and various strengthening mechanisms. Higher FSP passes lead to refined grain structure and DRX during processing, producing equiaxed grains that restrict dislocation movement, which in turn enhances microhardness. Increasing reinforcement particle concentration and FSP passes (from 1 to 5) suppressed grain boundary migration, leading to a reduction in both high-angle grain boundaries and overall grain size The optimized input parameters, SiC%, Al 2 O 3 %, and the number of FSP were observed as 67.98%, 3.33%, and 3.27, respectively. Correspondingly, the optimized output values for UTS, % strain, and microhardness value at the processes zone are perceived as 305.96 MPa, 17.36%, and 81.107 HV, respectively. These findings provide a comprehensive guide for achieving the best possible mechanical properties of MPFSP (Al 2 O 3 +SiC) of AZ91D.