Abstract
The effect of heat treatments on microstructure and mechanical properties of Al_0.5CoCrFeNi complex concentrated alloy (CCA) was studied. The CCA was prepared by vacuum induction melting of pure elements and solidification in ceramic crucibles. The as-solidified alloy was subjected to heat treatments consisting of solid solution annealing, water quenching and precipitation hardening. The microstructure of the as-solidified alloy consists of fcc(A1) dendrites and an interdendritic region composed of bcc(B2), bcc(A2) and fcc(A1) phases. The solution annealing followed by water quenching and ageing at 800 and 900 °C leads to the precipitation of needle-like bcc(B2) particles in fcc(A1) dendrites and the formation of the interdendritic region composed of bcc(B2) and fcc(A1) phases. The volume fraction of needle-like bcc(B2) precipitates increases with increasing ageing time and decreasing ageing temperature. The size of bcc(B2) precipitates increases with increasing ageing time and ageing temperature. Vickers microhardness, Vickers hardness and room temperature yield strength of the heat-treated alloy increase with decreasing ageing temperature and increasing ageing time up to 5 h and then decrease at a longer ageing time up to 25 h.

Key words
complex concentrated alloys, precipitation hardening, heat treatment, microstructure, mechanical properties

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