硫化钠对镀锌钢表面铈盐转化膜耐蚀性的影响

Effect of sodium sulfide on corrosion resistance of cerium-salt conversion coating on galvanized steel

采用硝酸亚铈、六偏磷酸钠组成的转化液,在镀锌钢表面制备了铈盐转化膜,研究了硫化钠(Na2S)对其耐蚀改性作用。通过中性盐雾(NSS)试验考察了Na2S质量浓度、p H、温度、时间等工艺条件对转化膜耐蚀性的影响,通过单因素试验得到最佳转化条件为:Na2S 6 g/L,温度25°C,p H 0.8,转化时间3 min。用扫描电镜和能谱分析了有无Na2S改性的铈盐转化膜的形貌结构及成分,用Tafel极化曲线法比较了它们的耐蚀性。结果表明,加入Na2S增强了铈盐转化膜与镀锌钢基体的附着力,提高了O、P、Ce等主要耐蚀成分的含量,耐盐雾腐蚀时间由改性前的24 h延长到改性后的96 h,耐蚀性显著提高。

A cerium salt conversion coating was prepared on galvanized steel in a bath mainly consisting of cerium（III） nitrate and sodium hexametaphosphate. The modification effect of sodium sulfide （Na2S） on corrosion resistance of the coating was studied. The influences of conversion conditions such as mass concentrations of Na2S, pH, temperature, and reaction time on corrosion resistance of the coating were studied by neutral salt spray （NSS） test. The optimal conditions were determined by single-factor experiment as follows： Na2S 6 g/L, temperature 25 C, pH 0.8, and time 3 min. The cerium-salt conversion coating obtained thereby was compared with the unmodified one. The surface morphology and elemental composition were analyzed by scanning electron microscopy and energy-disperse spectroscopy. The corrosion resistance was characterized by Tafel polarization measurement. The results showed that the addition of Na2S enhances the adhesion between the conversion coating and galvanized steel, and increases the contents of major anticorrosive components such as O, P, and Ce. The enduring time to NSS test of cerium-salt conversion coating prolongs from 24 h to 96 h after modification, showing an evident improvement of corrosion resistance.