Corrosion Resistance of Al0.5CoCrFeNiCuxAgy (x = 0.25, 0.5; y = 0, 0.1) High-Entropy Alloys in 0.5M H2SO4 Solution

The electrochemical behavior of the as-cast Al0.5CoCrFeNiCuxAgy (x = 0.25, 0.5; y = 0, 0.1) high-entropy alloys (HEAs) in a 0.5M H2SO4 solution was studied. Polarization measurements were carried out in a standard three-electrode electrochemical cell at room temperature using a platinum counter electrode and a saturated silver chloride reference electrode. For Al0.5CoCrFeNiCu0.5 and Al0.5CoCrFeNiCu0.5Ag0.1, copper segregation along the grain boundaries was observed, which highly dissolved in the sulfuric acid solution and resulted in low corrosion resistance of the samples. Introducing Ag into Al0.5CoCrFeNiCu0.25 HEA led to the precipitation of a copper–silver eutectic structure, in which the copper regions were selectively dissolved in the sulfuric acid solution. Al0.5CoCrFeNiCu0.25 exhibited the best corrosion resistance with the corrosion current density of Icorr = 3.52 ± 0.02 μA/cm2, significantly superior to that of the Al0.5CoCrFeNi sample without copper and silver (Icorr = 6.05 ± 0.05 μA/cm2). Finally, the results indicated that suppressing elemental segregation by annealing or tailoring chemical composition is essential to improve the corrosion resistance of Al0.5CoCrFeNiCuxAgy HEAs.