NH4F浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响

目的 考察乙二醇-氟化铵电解液中氟化铵浓度对镁合金表面微弧氧化制备氟化物膜层结构和性能的影响，提高镁合金氟化物膜层的耐腐蚀性能。方法 在含不同浓度NH4F的EG-NH4F电解液中，采用微弧氧化的方法制备氟化物膜层，NH4F质量浓度分别为40、60、80、100、120 g/L。通过扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)和X射线衍射仪(XRD)，对膜层表面微观形貌和成分组成进行分析，并通过电化学测试表征了膜层的腐蚀防护性能，通过盐雾试验评估了膜层长效防腐蚀行为，通过SEM和EDS表征了腐蚀形貌和腐蚀产物。结果 在EG-NH4F中制备膜层的物相组成主要是MgF2。随着NH4F浓度的提高，微弧氧化的起弧电压与工作电压均逐渐减小，膜层中氟含量逐渐增加，膜层的孔径减小，孔数量分布更加均匀，膜层表面粗糙度降低。质量浓度为100 g/L NH4F的膜层自腐蚀电流密度(Jcorr)为2.226×10^?7 A/cm²，较镁合金基材降低了1个数量级，极化电阻Rp增大到90.156 kΩ.cm²，其阻抗模量|Z|f=0.01 Hz=8.55×10⁵ Ω.cm²，与镁合金基材的阻抗模量|Z|f=0.01 Hz=8.86×10² Ω.cm²相比，提高了3个数量级。结论 微弧氧化处理能够显著改善AZ31镁合金的腐蚀防护性能。NH4F浓度的增加有利于提高膜层的耐腐蚀性能，质量浓度为100 g/L NH4F的膜层耐腐蚀性能最优。

Effect of NH4F Concentration on Microstructure and Properties of Fluoride Coatings on Magnesium Alloy by Plasma Electrolytic Oxidation

This work aims to study the effect of NH4F concentration on phase composition, microstructure and corrosion resistance of fluoride coatings on AZ31 magnesium alloy in EG-NH4F electrolytic solution by plasma electrolytic oxidation (PEO). The EG-NH4F electrolytic solutions with NH4F concentration of 40 g/L, 60 g/L, 80 g/L, 100 g/L and 120 g/L were used to prepare PEO coatings on AZ31 magnesium alloy. A scanning electron microscope (SEM), an X-ray energy dispersion spectrometer (EDS) and an X-ray diffractometer (XRD) were used to analyze the surface morphology and composition of the coatings. The electrochemical corrosion behavior was evaluated by potentiodynamic polarization tests in neutral corrosive media, while the long-term corrosion behavior by salt spray tests. The corrosion morphologies and corrosion products after salt spray tests were characterized by the SEM and the EDS. The coating was mainly composed of MgF2. The working voltage and breakdown voltage of PEO process decreased gradually with the increase of the NH4F concentration. The pore size and surface roughness of the coating decreased. The MgF2 coating can significantly improve the corrosion resistance of AZ31 magnesium alloy, and the coating prepared at 100 g/L NH4F has optimal corrosion protection performance.