Friction stir processing is performed on RZ 5 Mg alloy to produce surface metal matrix composites reinforced with hard reinforcement particles. Boron carbide, multiwalled carbon nanotubes, and a mixture of zirconia and alumina particle reinforcements were introduced. The developed surface composites (SCs) exhibited lower wear rates at various normal loads than the base RZ 5 Mg alloy owing to their improved microhardness. The wear resistance of the composites was 1.2–1.9 times greater than the base alloy, and hence, the wear rates were 18–50% lower than the base alloy. Maximum reduction in wear rate is observed in B₄C-reinforced SC. Abrasion, adhesion, and oxidative wear mechanisms are operational during the wear test performed at loads ranging between 10 N and 75 N.