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<p>To evaluate the corrosion resistance of KMgF<sub>3</sub> conversion coatings on AZ31 magnesium alloy in sodium sulfate environments (0.1&#xa0;M, 0.3&#xa0;M, 0.5&#xa0;M Na<sub>2</sub>SO<sub>4</sub>), this study employed hydrogen evolution tests and electrochemical measurements. The coatings were prepared by immersing the alloy in a 0.1-M KF solution prior to testing. Surface morphology and phase composition were characterized by scanning electron microscopy (SEM) and<i> x</i>-ray diffraction (XRD) to elucidate the corrosion mechanism. The results revealed that the KMgF<sub>3</sub> coating gradually dissolved, forming a porous corrosion-product layer primarily composed of MgO and Mg(OH)<sub>2</sub>. Corrosion resistance exhibited a non-monotonic trend during immersion: It initially decreased due to coating dissolution, temporarily improved as the corrosion-product layer formed, and subsequently declined as the layer deteriorated. Optimal corrosion performance was observed after approximately 24&#xa0;h. Higher Na<sub>2</sub>SO<sub>4</sub> concentrations accelerated the coating degradation, reduced the peak corrosion resistance, and increased the overall corrosion rate. SO<sub>4</sub><sup>2−</sup> ions promoted degradation via competitive adsorption, formation of soluble MgSO<sub>4</sub>, and the disruption of Mg(OH)<sub>2</sub> layer stability.</p>

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Non-Monotonic Evolution of Corrosion Performance: The Failure Mechanism of KMgF3-Coated AZ31 Mg Alloy in Sulfate Environments

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • Yanzhe Yang,
  • Yu Zhang,
  • Lin Zhao,
  • Pengyu Dai,
  • Xiaohong Yi

摘要

To evaluate the corrosion resistance of KMgF3 conversion coatings on AZ31 magnesium alloy in sodium sulfate environments (0.1 M, 0.3 M, 0.5 M Na2SO4), this study employed hydrogen evolution tests and electrochemical measurements. The coatings were prepared by immersing the alloy in a 0.1-M KF solution prior to testing. Surface morphology and phase composition were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD) to elucidate the corrosion mechanism. The results revealed that the KMgF3 coating gradually dissolved, forming a porous corrosion-product layer primarily composed of MgO and Mg(OH)2. Corrosion resistance exhibited a non-monotonic trend during immersion: It initially decreased due to coating dissolution, temporarily improved as the corrosion-product layer formed, and subsequently declined as the layer deteriorated. Optimal corrosion performance was observed after approximately 24 h. Higher Na2SO4 concentrations accelerated the coating degradation, reduced the peak corrosion resistance, and increased the overall corrosion rate. SO42− ions promoted degradation via competitive adsorption, formation of soluble MgSO4, and the disruption of Mg(OH)2 layer stability.