Corrosion behavior of CoCrNiAl high entropy alloy and other typical metals in simulated acid rain solution

Abstract

In order to study the accelerated electrochemical corrosion behavior under simulated acid rain, CoCrNiAl high entropy alloy (HEA) was prepared. The electrochemical performance of CoCrNiAl HEA and other typical metals (Q235 steel, AZ31 magnesium alloy, and 1060 aluminum alloy) in simulated acid rain solution with different pH (3.5, 4.0, 4.5, and 5.0) were studied. The results show that the microstructure of CoCrNiAl HEA is mainly composed of dendrites (DR). The alloy exhibits the diffraction patterns of the disordered A2-bcc phase with the ordered B2-bcc phase. Ni-Al is rich in dendrites, and Cr is rich in interdendritic (ID) regions that consist of the A2/B2. The CoCrNiAl HEA has excellent corrosion resistance in simulated acid rain solution with pH = 3.5, 4.0, 4.5, and 5.0. The self-corrosion current is reduced by 1-2 orders of magnitude compared with other typical metals. The self-corrosion potential is higher than for other typical metals except in a solution with pH = 5. The CoCrNiAl HEA has excellent pitting corrosion resistance. The corrosion resistance of CoCrNiAl HEA is related to the uniformity and compactness of the microstructure, passive surface film, and corrosion resistant elements in the alloy. The dense corrosion products on the surface also play a role in reducing the corrosion rate. The corrosion mechanism of the prepared CoCrNiAl alloy is intergranular corrosion when it comes into contact with a simulated acid rain solution, and then with the extension of time, the corrosion mechanism changes to uniform corrosion. K e y w o r d s : corrosion performance, high entropy alloy, simulated acid rain, vacuum casting, microstructure