The Al_0.5CoCrFeNi high-entropy alloy was smelted by vacuum medium frequency induction melting, followed by homogenization heat-treatment and cold rolling with 40% reduction, and then post-heat treatment at 800, 1000 and 1200 ℃ respectively. The microstructure and mechanical properties, as well as the corrosion behavior in solutions of 0.5 mol/L H₂SO₄, 0.5 mol/L NaOH and 3.5%NaCl of as the cast alloy and the rolled + post heat-treated alloys were studied by XRD, SEM, EDS, AFM, universal testing machine and electrochemical corrosion test. The microstructure analysis shows that the as-cast high entropy alloy has a typical dendrite structure composed of fcc-phase and bcc-phase (B2) with precipitates of flocculent structure-like fine fcc-phase within the B2-phase, however after rolling+heat treatment, the fine fcc-phase within the B2 phase is completely dissolved, while certain amount of acicular B2-phase is precipitated within the fcc-phase. Mechanical analysis shows that the precipitation of the hard and brittle acicular B2-phase increases the yield strength and hardness of the alloy. After rolling + heat treatment, the potential difference within the B2 phase is eliminated, but the potential difference between B2-phase and fcc-phase is increased, nevertheless, which gradually decreases with the increase of heat treatment temperature. The electrochemical corrosion test results show that in 0.5 mol/L H₂SO₄ solution, the corrosion properties of the alloy at different temperatures are linearly related to the Cr content in B2-phase. In 0.5 mol/L NaOH solution, the as-cast alloy and rolled + 1000 ℃ heat treated alloy showed excellent corrosion resistance. In contrast, the rolled + 1200 ℃ heat treated alloy has the best corrosion resistance in 3.5%NaCl solution.