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<p>In this study, ZnCo alloy coatings were electrodeposited on Q235B steel to enhance its corrosion resistance, followed by trivalent chromium-molybdate passivation for additional protection. The deposition mechanism, surface morphology, roughness, chemical composition and corrosion behavior of Zn, ZnCo and passivated ZnCo coatings were systematically investigated. During electrodeposition, Zn<sup>2+</sup> and Co<sup>2+</sup> ions were coreduced onto the cathode surface, with Co being preferentially deposited at lower current densities, resulting in a compact alloy structure. The subsequent passivation involved the formation of a Cr(III)-Mo oxide film, primarily composed of Cr<sub>2</sub>O<sub>3</sub> and MoO<sub>2</sub>, which acted as an effective corrosion barrier. Energy-dispersive spectroscopy confirmed that the passivated ZnCo coating was composed of Zn (80.2&#xa0;wt.%), Co (19.8&#xa0;wt.%), Cr (13.9&#xa0;wt.%) and Mo (7.3&#xa0;wt.%). After immersion in 3.5% NaCl solution for seven days, the passivated ZnCo coating exhibited the lowest surface roughness (0.492&#xa0;μm) and corrosion current density (0.689&#xa0;μA&#xa0;cm<sup>−2</sup>), demonstrating superior corrosion resistance. The synergistic effect of Cr and Mo within the passive film provides durable protection and significantly enhances the corrosion performance of ZnCo-coated Q235B steel.</p>

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Deposition Mechanism and Corrosion Resistance of Electrodeposited ZnCo Coatings Passivated by Trivalent Chromium and Molybdate

  • 期刊论文

  • 发表日期：

    2025年12月17日

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  • Li Guoqiang,
  • Gong Hui,
  • Jin Yin,
  • Zhang Ping

摘要

In this study, ZnCo alloy coatings were electrodeposited on Q235B steel to enhance its corrosion resistance, followed by trivalent chromium-molybdate passivation for additional protection. The deposition mechanism, surface morphology, roughness, chemical composition and corrosion behavior of Zn, ZnCo and passivated ZnCo coatings were systematically investigated. During electrodeposition, Zn2+ and Co2+ ions were coreduced onto the cathode surface, with Co being preferentially deposited at lower current densities, resulting in a compact alloy structure. The subsequent passivation involved the formation of a Cr(III)-Mo oxide film, primarily composed of Cr2O3 and MoO2, which acted as an effective corrosion barrier. Energy-dispersive spectroscopy confirmed that the passivated ZnCo coating was composed of Zn (80.2 wt.%), Co (19.8 wt.%), Cr (13.9 wt.%) and Mo (7.3 wt.%). After immersion in 3.5% NaCl solution for seven days, the passivated ZnCo coating exhibited the lowest surface roughness (0.492 μm) and corrosion current density (0.689 μA cm−2), demonstrating superior corrosion resistance. The synergistic effect of Cr and Mo within the passive film provides durable protection and significantly enhances the corrosion performance of ZnCo-coated Q235B steel.