钝化法热浸镀铝钝化液配方的正交优化

Orthogonal Optimization of Passivator of Passivating Hot-Dip Aluminizing

为了在保证钝化热浸镀铝层质量的基础上减轻钝化液毒性,通过添加NaNO_2和KMnO_4来降低铬酐钝化液中CrO_3的含量,经2次正交优化试验获得4种低CrO_3的钝化液,可使CrO_3浓度降低至原来的1/10,经低CrO_3含量钝化液处理的试样可获得表面光滑、连续完整的镀层。由硝酸腐蚀失重试验分析4种经较优钝化液处理、宏观镀层完好的试样的失重,确定可获得无针孔镀层的钝化液组成为3 g/L CrO_3,2 g/L NaNO_2,0.1 g/L KMnO_4;借助扫描电镜观察,对最佳镀层的显微结构进行分析,结果显示镀层从外到内分别由纯铝层和合金层构成,铝层较薄,约20μm,合金层较厚,约70μm,合金层与基体呈锯齿状相结合。

In order to reduce the toxicity of passivation solution on the prerequisite for ensuring the quality of passivating hot-dip aluminizing,the content of CrO3 in chromic anhydride passivation solution was reduced by adding NaNO2 and KMnO4. After two orthogonal optimization experiments,four kinds of low CrO3 passivation solution were obtained,which could reduce the content of CrO3 to 1/10 of that of the original solution. After treated by the low CrO3 passivation solution,the sleek,continuous and complete coatings were obtained. Nitric acid corrosion weight-loss test was used to analyze the weight loss of intact coatings prepared by the four kinds of optimized solution,and the optimal solution in which the coating with free pinhole was obtained was confirmed 3 g/L CrO3,2 g/L NaNO2 and 0.1 g/L KMnO4. Moreover,the structure of optimal coating was observed by using scanning electron microscope( SEM),and it was found that the coating was composed of pure Al layer and alloy layer from the outer to the inner. The Al layer was thinner( about 20 μm) while the alloy layer was thicker( about 70 μm). Besides,the two layers were saw-toothed jointed with each other.