Severe Plastic Deformation of Al–Mg–Si Alloy: The Role of Threaded Pin Profiles in Achieving Grain Refinement Through Friction Stir Processing

Friction stir processing (FSP) of Al–Mg–Si alloys is a severe plastic deformation technique for enhancing material properties through controlled microstructural evolution. The objective of this study is to investigate the effect of several pin profiles, namely tapered, cylindrical, and cylindrical threaded pin profiles, on the mechanical characteristics and microstructure of FSPed Al–Mg–Si alloy. The microstructural changes caused by each pin profile have been investigated with optical microscopy and SEM. Furthermore, microhardness, tensile, and fracture morphology tests have been employed to evaluate the mechanical properties. The unique microstructural characteristics, like grain size and distribution, that are impacted by the particular deformation mechanisms connected to every pin profile were revealed by optical microscopy results. SEM analysis shed light on the precipitation behavior and demonstrated the complex interactions between threading and tapering and the alloy’s finer-scale properties. The hardness profiles throughout the stir zone were acquired in order to comprehend the mechanical behavior of the processed specimen. The threading operation enhanced the hardness characteristics and polished the grain structures, especially in the cylindrical threaded pin profile. The pin profile that was employed during processing caused variances in the tensile qualities, such as strength and ductility. The examination of the fracture surface demonstrated how the pin profiles, with their distinct morphologies, void forms, and ductile properties, affected the failure mechanisms.