Effect of Heat Treatment on Corrosion of an AlCoCrFeNi2.1 Eutectic High-Entropy Alloy in 3.5 wt% NaCl Solution

This paper studies how heat treatments influence the corrosion of an AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) in a 3.5 wt% NaCl solution, by comparing the corrosion behaviors of as-cast, 600 °C heat-treated, and 1000 °C heat-treated samples using microstructure characterization, electrochemical measurements, and surface characterization. The electrochemical results show that the pitting potential rises and the passive current density and passive film resistance are almost changeless with an increasing heat treatment temperature. The enhancement in the pitting corrosion resistance results from the increased amount of the Cr-rich FCC phase and decreased amount of the B2 phase rich in the Al element, which are induced by the heat treatment. On one hand, this microstructure evolution can make the passive film have more Cr2O3 and less Al2O3, thereby enhancing its protective properties, as confirmed by the X-ray photoelectron spectroscopy analysis. On the other hand, the decreased amount of the Al-rich B2 phase can make the pitting corrosion less prone to initiate since the B2 phase can act as the pit initiation site, which is supported by the observation of corrosion morphologies, due to its higher electrochemical activity. In a summary, the heat treatment is beneficial for improving the pitting corrosion resistance of the AlCoCrFeNi2.1 EHEA.