AZ91D镁合金锰系磷酸盐转化膜的研究:磷化液各组分及含量对耐蚀性能的影响

Research on Manganese-based Phosphate Conversion Coating on AZ91D Magnesium Alloy: the Effect of Various Components and Contents of Phosphating Solution on Corrosion Resistance

研究不同添加剂对磷化膜耐腐蚀性能的影响,提高镁合金锰系磷化膜的耐腐蚀性能。利用化学转化法在AZ91D镁合金表面制备锰系磷化膜。研究磷化液的组分及含量对磷化膜耐蚀性能的影响,利用SEM、EDS对膜层表面形貌、元素组成进行表征;通过电化学行为和点滴试验对转化膜的耐腐蚀性能进行分析判断。磷化液各组分的最佳质量浓度为:35 g/L MnSO_(4)、30 g/L NaH_(2)PO_(4)、0.5 g/L EDTA⁃4Na、1 g/L NaF、2 g/L NaNO_(3),pH=2.5(用磷酸调节pH)。在电镜图中观察到镁合金磷化膜有明显的双层膜结构,且膜层的厚度约为24μm。优化后磷化膜的厚度更厚,表面更加致密,裂纹数量更少。在EDS中观察,加入NaF后,膜层的组成物质变化,有少量的F元素参与成膜。相比基础磷化膜,优化后的磷化膜耐腐蚀性增加,腐蚀电流密度从8.912×10^(-7)A/cm^(2)减小为5.56×10^(-7)A/cm^(2),容抗弧半径也有明显的增大,耐蚀性能得到提升。

This research was aimed to explore the influence of different additives on the corrosion resistance of phosphating coatings,and to improve the corrosion resistance of manganese-based phosphating coatings on magnesium alloys.The manganese-based phosphating film was prepared on the surface of AZ91 D magnesium alloy by the chemical conversion method.The influence of the composition and content of the phosphating solution on the corrosion resistance of the phosphating film was explored,and the surface morphology and composition of the film were characterized by SEM and EDS analyses.The optimum mass concentration of each component in phosphating solution was 35 g/L MnSO_(4),30 g/L NaH_(2)PO_(4),0.5 g/L EDTA-4 Na,1 g/L NaF,and 2 g/L NaNO_(3)(pH=2.5 with phosphoric acid).In the SEM image,the magnesium alloy phosphating film displayed an obvious double-layer film structure,and the thickness of the film layer was about 24μm.Through SEM observation,the thicker the optimized phosphating film,the more dense surface and fewer cracks were found.It was observed in the EDS diagram that after the addition of NaF,the composition of the film layer changed,and a small number of F element participated in the film formation.Compared with the basic phosphating film,the corrosion resistance of the optimized phosphating film was enhanced,the corrosion current density was reduced from 8.912×10^(-7)A/cm^(2)to 5.56×10^(-7)A/cm^(2),and the capacitive arc radius was also significantly increased.Overall,the corrosion resistance performance was greatly improved.