Microstructures of Al7.5Cr22.5Fe35Mn20Ni15 High-Entropy Alloy and Its Polarization Behaviors in Sulfuric Acid, Nitric Acid and Hydrochloric Acid Solutions

This paper investigates the microstructures and the polarization behaviors of Al7.5Cr22.5Fe35Mn20Ni15 high-entropy alloy in 1M (1 mol/L) deaerated sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) solutions at temperatures of 30–60 ̋C. The three phases of the Al7.5Cr22.5Fe35Mn20Ni15 high-entropy alloy are body-centered cubic (BCC) dendrites, face-centered cubic (FCC) interdendrites, and ordered BCC precipitates uniformly dispersed in the BCC dendrites. The different phases were corroded in different acidic solutions. The passivation regions of the Al7.5Cr22.5Fe35Mn20Ni15 alloy are divided into three and two sub-regions in the solutions of H2SO4 and HNO3 at 30–60 ̋C, respectively. The passivation region of the Al7.5Cr22.5Fe35Mn20Ni15 alloy is also divided into two sub-domains in 1M deaerated HCl solution at 30 ̋C. The Al7.5Cr22.5Fe35Mn20Ni15 alloy has almost equal corrosion resistance in comparison with 304 stainless steel (304SS) in both the 1M H2SO4 and 1M HCl solutions. The polarization behaviors indicated that the Al7.5Cr22.5Fe35Mn20Ni15 alloy possessed much better corrosion resistance than 304SS in 1M HNO3 solution. However, in 1M NaCl solution, the corrosion resistance of the Al7.5Cr22.5Fe35Mn20Ni15 alloy was less than 304SS.