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

Highlights: • Effect of Al on the corrosion behavior of HEA in acidic solutions was studied. • The film thickness was obtained combined with the results of EIS and AES. • The increasing Al content in the HEA had a positive effect in H₂SO₄ solution. • The increasing Al content in the HEA had a negative effect in HCl solution. 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 FeCoCrNiAl_x (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. FeCoCrNiAl_0.3 alloy still remains the stable FCC substrate without any second phase precipitates. The increasing aluminum content can improve the corrosion resistance of FeCoCrNiAl_x 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.