Microstructural, Microhardness and tribological analysis of cooling-assisted friction stir processing of high-entropy alloy particles reinforced aluminum alloy surface composites

High-entropy alloy (HEA) is a promising reinforcing material for aluminium alloys. In this work, cooling-assisted friction stir processing was applied to produce aluminium alloy surface composites reinforced with HEA particles. The effects of the volume fraction of HEA particles on the microstructure, microhardness and tribological properties were studied. The fabricated composites had uniformly distributed HEA particles and showed an excellent interfacial bonding between HEA particles and the matrix. The grain size of the fabricated composites was more refined than that of the base metal, and the grain sizes of the composites with 5 vol.%, 10 vol.% and 15 vol.% HEA particles were refined from a range of 2-15 m of aluminium matrix to 1.8, 1.4 and 1.1 m, respectively. The increased volume fraction of HEA particles caused an improvement in hardness and wear resistance. The composites reinforced with 15 vol.% HEA particles showed a 65.9% increase in hardness, a 43.0% reduction in wear rate and a 57.8% reduction in wear loss compared with those of the base metal. The wear mechanism was transformed from adhesive wear in the base metal to abrasive wear in Al-15 vol.% HEA surface composites.