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.