Plasma electrolytic oxidation coatings were prepared in aluminate, phosphate, and silicate-based electrolytic solutions using a soft-sparking regime in a multi-frequency stepped process to compare the structure, corrosion, and wear characteristics of the obtained coatings on AZ31 magnesium alloy. The XRD results indicated that all coatings consist of MgO and MgF₂, while specific products such as Mg₂SiO₄, MgSiO₃, Mg₂P₂O₇, and MgAl₂O₄ were also present in specimens based on the selected solution. Surface morphology of the obtained coatings was strongly affected by the electrolyte composition. Aluminate-containing coating showed volcano-like, nodular particles and craters distributed over the surface. Phosphate-containing coating presented a sintering-crater structure, with non-uniform distributions of micro-pores and micro-cracks. Silicate-containing coating exhibited a scaffold surface involving a network of numerous micro-pores and oxide granules. The aluminate-treated sample offered the highest corrosion resistance and the minimum wear rate (5 × 10⁻⁵ mm³ N⁻¹ m⁻¹), owing to its compact structure containing solely 1.75% relative porosity, which is the lowest value in comparison with other samples. The silicate-treated sample was degraded faster in long-term corrosion and wear tests due to its porous structure, and with more delay in the phosphate-containing coating due to its larger thickness (30 µm).

中文翻译：

---

电解液成分对AZ31镁合金上PEO涂层的结构，腐蚀和耐磨性的影响

在铝酸盐，磷酸盐和硅酸盐基电解液中使用软火花工艺在多频分步工艺中制备等离子体电解氧化涂层，以比较所得的AZ31镁合金涂层的结构，腐蚀和磨损特性。X射线衍射（XRD）结果表明，所有涂层均由MgO和MgF _2组成，而特定产品如Mg ₂ SiO ₄，MgSiO ₃，Mg ₂ P ₂ O ₇和MgAl ₂ O _4等。根据选定的溶液，样品中也存在。所获得的涂层的表面形态受电解质组成的强烈影响。含铝酸盐的涂层显示出火山状结节状颗粒和火山口分布在表面。含磷酸盐的涂层呈现出烧结坑结构，具有微孔和微裂纹的不均匀分布。含硅酸盐的涂层表现出包括许多微孔和氧化物颗粒的网络的支架表面。经铝酸盐处理的样品具有最高的耐腐蚀性和最低的磨损率（5×10 ^-5 mm ³ N ^-1 m ^-1），因为其紧凑的结构仅包含1.75％的相对孔隙度，这是与其他样品相比最低的值。经硅酸盐处理的样品由于其多孔结构而在长期腐蚀和磨损测试中降解得更快，并且由于其较大的厚度（30 µm）而使含磷酸盐的涂层具有更大的延迟。