植酸处理对LZ91镁锂合金腐蚀性能的影响

Effect of Phytic Acid Treatment on Corrosion Properties of LZ91 Magne‐sium Lithium Alloy

对厚度3 mm的LZ91镁锂合金在不同转化时间下进行了植酸化学转化处理。采用扫描电子显微镜、X射线能谱仪、电化学工作站等设备对不同植酸转化时间生成的转化膜的形貌、转化膜成分、腐蚀性能和成膜工艺进行了测试和分析。结果表明,当植酸浓度、植酸溶液pH值和转化温度分别保持2 mL/L、6和55℃不变,转化时间在2~15 min之间时,LZ91镁锂合金表面生成的转化膜良好,转化膜上生成了难溶的白色颗粒状锌的螯合物。随着植酸处理转化时间的增加,转化膜的龟裂纹呈现出逐渐由浅变深的趋势,转化膜厚度呈现出先增大后减小的现象,LZ91镁锂合金植酸处理后的耐腐蚀性能先上升后下降,当转化时间为5 min时,LZ91镁锂合金植酸处理后的耐腐蚀性能最好,其自腐蚀电流密度最小为3.76×10^(-5)A/cm^(2),相比植酸处理前的自腐蚀电流密度下降了2个数量级,此时为植酸处理LZ91镁锂合金形成转化膜的最佳时间。

LZ91 magnesium lithium alloy with a thickness of 3 mm was treated with phytic acid chemical conversion method under different conversion times.The morphology,composition,corrosion performance and film-forming process of the conversion film formed at different phytic acid conversion time were tested and analyzed by scanning electron microscope,X-ray energy spectrometer and electrochemical workstation.The results show that when the phytic acid concentration,pH value of phytic acid solution and conversion temperature remain unchanged at 2 mL/L,6 and 55℃ respectively,and the conversion time is between 2 and 15 min,the conversion film formed on the surface of LZ91 magnesium lithium alloy is good,and the insoluble white granular zinc chelate is formed on the conversion film.With the increase of phytic acid treatment conversion time,the tortoise crack of conversion film gradually changes from shallow to deep,the thickness of conversion film first increases and then decreases,and the corrosion resistance of LZ91 magnesium lithium alloy after phytic acid treatment first increases and then decreases.When the conversion time is 5 min,the corrosion resistance of LZ91 magnesium lithium alloy after phytic acid treatment is the best,and its self-corrosion current density is the minimum of 3.76×10^(-5) A/cm^(2),compared with the self-corrosion before phytic acid treatment,its value decreased by 2 orders of magnitude,which indicates that 5 min is the best time for phytic acid treatment of LZ91 magnesium lithium alloy to form conversion film.