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研究了AZ31B镁合金在羟基乙叉二膦酸(HEDP)溶液中的转化行为,并初步探讨了双膦酸化学转化体系的沉淀吸附防护机理。运用动电位极化扫描和极化阻抗法,比较分析了不同pH和HEDP浓度时转化膜的耐蚀性。结果表明,pH是关键影响因素。pH=1值时转化膜的耐蚀性最佳,腐蚀电位正移0.25 V,腐蚀电流密度降低近2个数量级(从57.3μA/cm2降至0.8μA/cm2),明显提高了镁合金的耐蚀性能。通过扫描电镜(SEM)分析表观形貌得知,膜层呈干涸河床状网络裂纹结构,且随pH升高,裂纹的宽度与深度增大,不利于膜层的抗腐蚀。
The conversion behavior of AZ31B magnesium alloy in hydroxyethylidenediphosphonic acid (HEDP) solution was studied. The mechanism of precipitation adsorption protection of bisphosphonic acid chemical conversion system was also discussed. The potentiostatic polarization and polarization impedance methods were used to analyze the corrosion resistance of the conversion coatings at different pH and HEDP concentrations. The results show that pH is the key factor. At pH = 1, the corrosion resistance of the conversion coating is the best. The corrosion potential shifts by 0.25 V and the corrosion current density decreases by nearly two orders of magnitude (from 57.3 μA / cm2 to 0.8 μA / cm2) Erosion performance. Scanning electron microscopy (SEM) analysis of the apparent topography showed that the membrane layer was dry river bed-like network crack structure, and with the increase of pH, the crack width and depth increases, is not conducive to corrosion resistance of the film.