The corrosion behavior and film properties of Al-containing high-entropy alloys in acidic solutions

Aluminum has shown promising application in reducing the high-entropy alloys’ weight and enhancing their mechanical properties. In this work, the impact of solid-solution aluminum on the corrosion behavior and film properties of FeCoCrNiAlx (x = 0.1, 0.3) high-entropy alloy in 0.5 M H2SO4 and 0.5 M HCl solutions was investigated by electrochemical measurement, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The results demonstrate that both of the high-entropy alloys exhibit an equiaxed grain structure with numerous annealing twins. FeCoCrNiAl0.3 alloy still remains the stable FCC substrate without any second phase precipitates. The increasing aluminum content can improve the corrosion resistance of FeCoCrNiAlx by simultaneously increasing Cr oxide content in the passive film and making it thicker in the H2SO4 solution. Nevertheless, the effect is negative in the HCl solution because chloride ions are inclined to combine with the Al-containing metastable ion complexes, which accelerates the dissolution of HEA.