This study examines the effects of heat treatment on corrosion behavior of equiatomic AlCoCrNiFe high-entropy alloy within a solution treatment temperature range of 800–1100 °C. Experimental observations on phase formation were compared with thermodynamic predictions. The microstructure, mechanical properties, and aqueous corrosion behavior of the as-deposited alloy were analyzed and contrasted with heat-treated samples. The results showed a decline in the corrosion resistance of the AlCoCrNiFe after heat treatment, which was attributed to chemical segregation and Cr depletion in the microstructure matrix. Additionally, post-corrosion analysis revealed a reduced volume fraction of protective oxides in the heat-treated samples.