Impact of innovative reinforcement strategies on microstructure, mechanical, and wear properties of magnesium-based surface composites produced by friction stir processing

Friction stir processing (FSP)is an effective technique for enhancing material properties by integrating reinforcing particles into a matrix. This study aims to synthesize a novel Mg-Al–Zn surface composite incorporating multiwall carbon nanotube (MWCNT) particles via FSP, and then to evaluate the effects of various processing strategies on particle distribution and material properties, including microstructure, mechanical properties, and tribological performance. Different innovative cavity designs (linear and zig-zag slots) were employed to incorporate MWCNT particles into the base material (BM). In addition, a revolutionary pitch, alternating tool-travel direction between passes, and multiple passes were used as key FSP parameters to induce severe plastic deformation. Results demonstrated uniform particle distribution, significant grain refinement from 33 µm in the BM to 2.65 µm in the linear slot design (LSD) and 4.7 µm in the zig-zag slot design (ZSD), a nearly 100% increase in microhardness, and up to an 82% improvement in tensile strength relative to the BM. Both designs showed improved wear resistance. These enhancements are caused by grain-boundary strengthening and microstructural refinement via continuous dynamic recrystallisation (CDRX). The present study shows that implementing the innovative strategies, such as LSD, achieved enhanced properties of the processed surface composite.