AZ91D镁合金植酸转化膜组成与耐蚀性能研究

Study of composition and corrosion protection afforded by phytic acid conversion coatings applied to AZ91D magnesium alloy

采用一种环保型金属处理剂植酸对AZ91D镁合金进行化学转化处理,并通过电化学测试技术和化学浸泡方法考查其耐蚀性能.结果表明,经植酸处理后,与传统的铬酸盐制品相比,在室温模拟汗液中,AZ91D镁合金的腐蚀电位从-1.6 V提高到-1.2 V(SCE);在相同电位下,阳极极化电流密度减小5个数量级,电化学性能得到显著改善.涂覆聚丙烯酸树脂后,在模拟汗液中浸泡72 h没有观察到腐蚀迹象.根据扫描电镜观察、电子能谱分析和衰减全反射红外光谱测试结果,发现植酸在镁合金表面发生化学吸附,以植酸盐的形式在合金表面形成一层致密的、具有网状裂纹的转化膜.该转化膜能够有效地阻止浸蚀性阴离子与金属基体接触,从而提高了镁合金的耐蚀性能.

Phytic acid, as an environmental-friendly agent, has been growing in the application of the metal surface treatment. The corrosion protection afforded by phytic acid conversion coatings on AZ91D magnesium alloy had been studied using DC polarization and chemical immersion techniques. The results show that compared with the coatings formed in chromate solution, the open-circuit potential of magnesium alloy coated by phytic acid solutions moves from - 1.6 V to - 1.2 V （SCE） and the anodic current density, at the same potential, decreases 5 orders of magnitude in simulated sweat fluid. After painted polyacrylic resin, magnesium alloy did not corrode during 72 h in the simulated sweat fluid. Based on the analysis of scanning electron microscope （SEM）, attenuated total reflectance （ATR） and energy dispersive X-ray detector （EDX）, it was concluded that with the combination of phytic acids and the metal, a compact film which had resillage was formed. It was mainly composed of phytate. This film may insulate the metal from the deleterious anion, thus protecting the magnesium alloy against corrosion.