This study reveals a novel approach to enhance the mechanical and wear properties of Mg alloy by incorporating high entropy alloy (HEA) particles, specifically CoCrFeNiMoTi particles following by carbon nano-tube (CNT) and graphene nano-plate (GNP) as a hybrid carbonaceous reinforcement via friction stir processing (FSP). The Mg/HEA-X% (CNT + GNP) surface composites (SCs) were systematically characterized in terms of microstructure, mechanical properties and wear surface morphology. The findings showed high efficiency of proper hybrid reinforcement content (HEA-1 % (CNT + GNP)) in grain refinement which was affected by the dynamic recrystallization (DRX), severe plastic deformation and Zener pinning by HEA, CNTs and carbide particles. The Mg and Mg/HEA SC exhibited micro hardness values of 33.5 and 57.5 HV and compressive strengths of 126 and 180 MPa, respectively. However, in Mg/HEA-1 % (CNT + GNP) SC, these properties were improved with increasing to 61 HV and 196 MPa about 6 % and 9 % improvement as compared to Mg/HEA SC, respectively. A remarkable synergy of strength-plasticity was achieved in Mg/HEA-1 % (CNT + GNP) SC due to the finest grain size, homogeneous distribution of reinforcement phase and kinematic hardening mechanism. In the normal loads of 10, 30 and 50 N, the coefficients of friction (FCs) and wear rates (WRs) were decreased by 13.8 %, 15.4 %, 16.3 % and 40 %, 26 %, 19 % in Mg/HEA-1 % (CNT + GNP) SC as compared to Mg/HEA SC, respectively. Superb wear resistance of Mg/HEA-1 % (CNT + GNP) SC was affected by the lowest grain size, high hardness, homogeneous distribution of reinforcement, well strength-plastic synergy and lubricating layers of GNP particles.

Keywords