Interface characteristics of high-entropy alloy/Al-Mg composites by underwater friction stir processing

•UFSP shows potential for fabricating the HEA reinforced Al matrix composite.•Mg and Cr segregation at the HEA-Al interface were observed.•Interface consists of FCC phase, Al18Cr2Mg3, and Cr-depleted HEA nanoparticles.•The composites show better mechanical and wear behaviors than reference alloys. A novel high-entropy alloy (HEA) reinforced Al-Mg composite has been produced by employing underwater friction stir processing (UFSP). A study of the HEA-Al interface reveals that Mg aggregation and Cr segregation occur at the interface, resulting in the formation of a dual interface composed of the FCC phase with a nanotwins structure, Al18Cr2Mg3, and HEA nanoparticles with the depletion of Cr. The tensile strength of the fabricated composites was enhanced to 401 MPa, which is 22.6% higher than that of the UFSPed Al-Mg alloy, and the friction coefficient was reduced from 0.45 to 0.29. Thus, the formed interface is beneficial to the load transfer from the matrix to the HEA particles.