Mechanical properties and microstructure of friction stir-welded AZ31 based on variety post-weld heat treatment (PWHT) temperatures were evaluated, and an optimal PWHT condition was identified. At rotational speed of 1200 rev min⁻¹ and welding speed of 300 mm min⁻¹, the average yield tensile, tensile strength and elongation of friction stir-welded joints was 92.5 MPa, 199.1 MPa and 7.3%, respectively. It was found that (300°C – 1 h) heat treatment after welding was more beneficial than other heat treatments in enhancing the mechanical properties and homogenising grain size. The maximum yield and tensile strength was 139.9 and 238.4 MPa, respectively, tensile longitudinal and compressive transverse residual stress could be effectively eliminated, and the fatigue strength increased 34.2% comparing with as-welded joints.

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 μ m of aluminium matrix to 1.8, 1.4 and 1.1 μ 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.