Heterogeneous structure-induced strength-ductility synergy by partial recrystallization during friction stir welding of a high-entropy alloy

To apply high-entropy alloys (HEAs) for extensive advanced structural uses, their welding properties should be well understood. In this study, Al _0.3 CoCrCu _0.3 FeNi HEA was butt welded by friction stir welding (FSW). The fine-grained partially recrystallized microstructure in the stir zone gave rise to a high tensile yield strength of 920 MPa with an elongation of 37%. By microstructural observation, the excellent mechanical properties of the stir zone material were attributed to the partially recrystallized heterogeneous structure, with which the synergetic strengthening improved the strength of the HEA with considerably less trade-off in its ductility. This unique phenomenon was unprecedented in any other friction-stir welded conventional alloys and was credited to the low stacking-fault energy and the high grain growth activation energy of the HEA. This work suggests that FSW can not only produce good HEA welds but serve as a special processing technique to enhance mechanical properties of HEAs.