Simultaneous enhancement of strength and ductility in an AlCoCrFeNi2.1 eutectic high-entropy alloy via friction stir processing

Highlights: • As-cast lamellar eutectic structure converted to ultrafine-grained microstructure. • The ultimate tensile strength increased from ∼1000 MPa to 1360 MPa. • Simultaneously, the ductility increased from ∼6.5% to 10%. Lamellar eutectic structure of as-cast AlCoCrFeNi_2.1 was tailored by friction stir processing (FSP). During FSP, lamellar B2 phase was broken into ultrafine-grained particles, with dissolution of Cr-rich precipitates in B2 and formation of Al-rich precipitates in FCC (L1₂). Dynamic recrystallization of FCC/L1₂ and B2 reduced grain size to less than ∼0.5 μm. The combined effect of microstructural evolution in the processed region improved the ultimate tensile strength from ∼1000 MPa to 1360 MPa, the ductility from ∼6.5% to 10%, and the microhardness from ∼300 HV0.2 to 450 HV0.2.