镁合金双稀土转化膜及其耐蚀性能的研究

Corrosion Resistance of Dual Rare Earth Conversion Film on Magnesium Alloy

已有的铬酸盐转化膜技术因污染环境而被限制使用。采用硝酸铈和硝酸镧混合溶液对AZ31镁合金进行了双稀土转化处理,讨论了浸渍时间对转化膜耐腐蚀性能的影响。采用点滴试验、盐水浸渍试验和Tafel极化法评价了双稀土转化膜的耐腐蚀性能。结果表明,经过双稀土处理后,镁合金的变色时间由6s提高到79s;在3.5%NaCl溶液中转化膜的腐蚀速率是基体的1/5;转化膜的腐蚀电位提高了0.313V,腐蚀电流密度由4.03×10-2mA/cm2降为2.31×10-4mA/cm2;双稀土转化膜的微观形貌呈破裂的干泥状;双稀土转化处理提高了镁合金的耐蚀性能,随处理时间的延长耐蚀性呈先增加后降低的趋势。

AZ31 Mg alloy substrates were soaked in the mixed solution of cerium nitrate and lanthanum nitrate to generate dual rare earth conversion film. The effect of immersion times on the properties of the conversion film was investigated, while the corrosion resistance of the conversion film was evaluated using dipping test, immersion test in saline water, and Tafel polarization method. Results indicated that the tarnishing time of Mg alloy was increased from 6 to 79 s after being soaked in the mixed rare earth solution. The corrosion rate of the conversion film in 3.5% NaCl solution was only 1/5 of that of Mg alloy substrate. At the same time, the corrosion potential of the conversion film was increased by 0. 313 V as compared with Mg alloy substrate, and the corrosion current density was reduced from 4.03×10-2to 2.31×10-4 mA/cm2. In one word, it was feasible to effectively increase the corrosion resistance of Mg alloy by dual rare earth conversion treatment, and the corrosion resistance of the conversion film tended to increase first and then decrease with extending time of immersion in the mixed rare earth solution.