This investigation studies the microstructures of FeCoNi and CrFeCoNi alloys, and their polarization behaviors in 1 M deaerated H2SO4 and NaCl solutions. The results revealed that both FeCoNi and CrFe-CoNi alloys had an FCC granular structure, and their lattice constants were approximately 0.357 nm in as cast and as-annealed states. However, many HCP precipitates were observed in the matrix of CrFeCoNi alloy in both as-cast and as-annealed states. The corrosion resistance of FeCoNi alloy in 1 M H2SO4 solution was better than that of CrFeCoNi alloy. The corrosion resistances of both FeCoNi and CrFeCoNi alloys in 1 M H2SO4 solution were better than that of 304 stainless steel. The corrosion resistance of FeCoNi alloy in 1 M NaCl solution was better than that of CrFeCoNi alloy. The activation energies of FeCoNi and CrFeCoNi alloys were calculated using the Arrhenius equation; in 1 M H2SO4 solution, they were 28.5 and 20.8 kJ/mol, respectively; and in 1 M NaCl solution, they were 24.6 and 89.1 kJ/mol, respectively. (C) 2016 Elsevier B.V. All rights reserved.