7075铝合金表面HEDP阳极氧化膜的微观结构及耐蚀、耐磨性能

Microstructure and corrosion/wear resistance of anodic oxide film prepared on 7075 aluminum alloy in HEDP electrolyte

[目的]探讨7075铝合金在羟基乙叉二膦酸(HEDP)溶液中阳极氧化的可行性,并分析氧化膜的结构、耐蚀性及耐磨性。[方法]考察了7075铝合金在HEDP电解液中进行恒电流阳极氧化时电压的变化趋势。通过扫描电镜(SEM)观察了不同氧化时间所得氧化膜的表面及截面微观形貌,通过动电位极化曲线、电化学阻抗谱和球-盘磨损试验评价了氧化膜的耐蚀性和耐磨性。[结果]7075铝合金在HEDP电解液中氧化过程的电压变化规律与典型多孔型氧化体系类似。HEDP阳极氧化膜呈双层结构,但其阻挡层明显厚于硫酸阳极氧化膜,表面孔径也更大。氧化时间为60min时可得到厚度约为13μm的膜层,其孔径为100~130 nm,阻挡层厚度为274 nm,在3.5%NaCl溶液中的腐蚀电流密度仅为相当厚度的硫酸氧化膜的10%,耐蚀性更佳。此外,HEDP阳极氧化膜还表现出良好的耐磨性,氧化60min和120min的HEDP氧化膜的摩擦因数仅为0.20~0.25,显著低于7075铝合金基体和硫酸阳极氧化膜。[结论]HEDP阳极氧化对7075铝合金耐蚀性和耐磨性的提高效果优于相同厚度的硫酸阳极氧化膜。

[Introduction]The feasibility of anodizing for 7075 aluminum alloy in 1-hydroxyethylidene-1,1-diphosphonic acid(HEDP)electrolyte was discussed,and the structure,corrosion resistance,and wear resistance of anodic oxide film were analyzed.[Method]The variation of voltage during constant-current anodization of 7075 aluminum alloy in HEDP electrolyte was studied.The surface and cross-sectional micromorphologies of the anodic oxide films obtained at different time were observed through scanning electron microscope(SEM).The corrosion resistance and wear resistance of the anodic oxide films was evaluated by potentiodynamic polarization curve measurement,electrochemical impedance spectroscopy(EIS),and ball-disc wear testing.[Result]The voltage variation of 7075 aluminum alloy during oxidation in HEDP electrolyte is similar to that of typical porous-type anodization.The anodic oxide film had a double-layered structure,but its barrier layer was much thicker and pore size larger as compared with that formed in sulfuric acid solution.A 13μm-thick anodic oxide film could be obtained when the oxidation time was 60 min,which had a pore size of 100-130 nm and a barrier layer thickness of 274 nm.Its corrosion current density in a 3.5%NaCl solution was only 10%of that of the anodic oxide film with a similar thickness formed in sulfuric acid solution,indicating that the anodic oxide film prepared in HEDP electrolyte had better corrosion resistance.The anodic oxide film prepared in HEDP electrolyte also exhibited good wear resistance.The friction coefficient of the anodic oxide film prepared by treating in HEDP electrolyte for 60 min and 120 m was only 0.20 to 0.25,which was much lower than that of 7075 aluminum alloy and the anodic oxide film formed in sulfuric acid solution.[Conclusion]The improvement effect of HEDP anodizing on the corrosion resistance and wear resistance of 7075 aluminum alloy is superior to that of sulfuric acid anodizing under the premise of the similar thickness.