Corrosion Resistance of Al_0.5CoCrFeNiCu _x Ag _y (x = 0.25, 0.5; y = 0, 0.1) High-Entropy Alloys in 0.5M H₂SO₄ Solution

The electrochemical behavior of the as-cast Al_0.5CoCrFeNiCu_xAg_y (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 Al_0.5CoCrFeNiCu_0.5 and Al_0.5CoCrFeNiCu_0.5Ag_0.1, 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 Al_0.5CoCrFeNiCu_0.25 HEA led to the precipitation of a copper-silver eutectic structure, in which the copper regions were selectively dissolved in the sulfuric acid solution. Al_0.5CoCrFeNiCu_0.25 exhibited the best corrosion resistance with the corrosion current density of I_corr = 3.52 ± 0.02 μA/cm², significantly superior to that of the Al_0.5CoCrFeNi sample without copper and silver (I_corr = 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 Al_0.5CoCrFeNiCu_xAg_y HEAs.