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目的：通过钼酸钠( SM)添加剂、SM前处理、SM后处理三种方案对铝合金表面植酸转化膜进行改进研究,以进一步提高其耐蚀性。方法通过动电位极化测试研究改进后铝合金在3.5%(质量分数) NaCl溶液中的耐蚀性。结果随着SM添加剂浓度的增加,铝合金表面植酸转化膜的耐蚀性先增强再减弱,SM质量浓度为30 g/L时的腐蚀保护效率P e 最大,达95.5%,而不含SM时的P e 仅为86.8%。 pH值太大(pH=8.0)或太小(pH=3.0)都不利于形成耐蚀性更好的膜层,pH值为6.0时的Pe 达98.6%。SM后处理会严重影响植酸转化膜的耐蚀性,腐蚀电流密度Jcorr大幅增大；SM前处理可提高植酸转化膜的耐蚀性,Pe达98.2%；SM前处理与添加剂同时应用时,植酸转化膜耐蚀性提高幅度更显著,Jcorr仅为0.042μA/cm2,极化电阻Rp达222 kΩ·cm2,Pe 达99.5%。结论 SM添加剂和SM前处理均可明显提高铝合金表面植酸转化膜的耐蚀性,且复合作用时的效果更显著,而SM后处理不能提高铝合金表面植酸转化膜的耐蚀性。

ABSTRACT:Objective To further enhance the corrosion resistance of phytic acid conversion coating on the surface of aluminum alloy, sodium molybdate ( SM) additives, SM pre-treatment and SM post-treatment were applied to modify the process. Methods The corrosion resistance of the modified aluminum alloy in 3. 5wt.% NaCl solution was investigated through dynamicpotential polar-ization test. Results With the increase in concentration of SM additives, the corrosion resistance of phytic acid conversion coating first increased and then decreased, and the corrosion protection efficiency Pe was the largest, reaching about 95. 5% when SM was 30 g/L, while the value was 86. 8% without SM additives. The Pe value reached 98. 6% at pH 6. 0, while a larger or a smaller pH (i. e. pH 8. 0 or pH 3. 0) was not beneficial to form a more anti-corrosion coating. However, the corrosion resistance of phytic acid conversion coating was seriously impaired by SM post-treatment, and the corrosion current density Jcor was substantially in-creased. SM pretreatment could enhance the corrosion resistance of phytic acid conversion coating, and Pe reached 98. 2%. When SM pretreatment and SM additives were applied simultaneously, the corrosion resistance of phytic acid conversion coating was im-proved most significantly, Jcor was merely 0. 042 μA/cm2;the polarization resistance Rp was 222 kΩ·cm2 , and Pe reached up to 99. 5%. Conclusion The corrosion resistance of phytic acid conversion coating on aluminum alloy could be largely enhanced by SM additives and SM pre-treatment, and the inhibition efficiency was more outstanding when these two modified schemes were applied simultaneously. However, SM post-treatment could not improve the corrosion resistance of phytic acid coating on aluminum alloy.