微弧氧化工艺参数对镁合金表面水滑石复合膜层耐蚀性的影响

Effect of Process Parameters on Corrosion Resistance of MAO/LDH Composite Coatings

目的通过在微弧氧化膜上原位生长水滑石膜,提高镁合金的耐蚀性。方法首先分别在硅酸盐、磷酸盐和铝酸盐为主的电解液体系中制备镁合金微弧氧化膜。然后采用水热处理技术,通过加入硝酸铝与硝酸锌的混合溶液,制备微弧氧化/水滑石复合膜层。采用扫描电镜、X射线衍射仪、接触角仪和电化学腐蚀试验,分别研究了微弧氧化及复合膜层的显微形貌、物相组成、疏水性和耐蚀性。结果XRD表明,在不同的微弧氧化膜上均可原位生成水滑石膜。铝酸盐体系中制备的水滑石膜厚且致密,硅酸盐和磷酸盐体系中生成的水滑石数量少,不能完全封闭微孔及裂纹。在硅酸盐体系中于400 V和430 V条件下制备的复合膜层,接触角分别为74.3°和130.3°。磷酸盐和铝酸盐中制备的复合膜层的接触角低,无疏水性。硅酸盐中于430 V条件下制备的复合膜层,阻抗模值达到2×10^(7)Ω×cm^(2),耐蚀性提高10倍左右。结论原位生长水滑石膜可以封闭微孔,硅酸盐和铝酸盐体系中制备的复合膜层的耐蚀性提高,磷酸盐体系中制备的复合膜层的耐蚀性下降。微弧氧化的成膜电压对水滑石生长无显著影响。

The work aims to improve the corrosion resistance of the micro-arc oxidation(MAO)coatings by layered double hydroxide(LDH).Firstly,the MAO coatings of Mg alloy were prepared in silicate,phosphate and aluminate-based electrolytes.Then the LDH was grown in situ on surface of MAO coatings.The samples were immersed in an autoclave and mixed with aluminum nitrate and zinc nitrate solution.Scanning electron microscopy,XRD,water contact angle measuring system and electrochemical corrosion tests were used to explore the micromorphology,composition and corrosion resistance of the coatings.The experimental results show that the LDH layer formed in aluminate system is thick and dense,while the amount of hydrotalcite was small and micro-pores and micro-cracks of MAO coatings were not completely closed by LDH in silicate and phosphate system.The results of XRD indicated that LDH had grown in situ on surface of MAO coatings.In silicate system,the contact angles of the composite coatings prepared under 400 V and 430 V conditions were 74.3°and 130.3°,respectively.The composite coating prepared in phosphate and aluminate has a low contact angle,without a hydrophobic.In silicate system,the composite coating prepared at 430 V has an impedance modulus of composite film of 2×10^(7)Ω×cm^(2),with the corrosion resistance increasing by about 10 times.In situ LDH has a great influence on the corrosion resistance of the coating,and the voltage has no significant influence on the LDH.