磷化处理对无铬钝化热镀锌板耐蚀性能的影响

研究了磷化处理工艺对无铬钝化热镀锌板耐腐蚀性能和表面形貌的影响。采用扫描电镜对其表面形貌进行分析,同时与未经过磷化处理的钝化板表面形貌进行对比;采用电化学阳极极化曲线方法和电化学阻抗法对磷化处理后钝化板的耐腐蚀性能进行了研究。在钝化板膜重为0.8g/m2的情况下,经磷化处理的钝化板表面钝化膜完好,没有发现锈蚀或钝化膜剥落现象;经磷化处理的钝化板自腐蚀电位和阳极电流密度不变,阴极电流密度和自腐蚀电流密度有所提高;Nyquist图的高频部分在磷化处理前为容抗弧,磷化处理后出现具有Warburg阻抗的直线,说明磷化处理后钝化膜表面出现扩散过程。研究表明,钝化板经过磷化处理后表面未形成磷化膜,耐腐蚀性能仍来自原钝化膜,经磷化处理的钝化板的耐腐蚀性能有所降低。因此,现有常规的磷化处理并没有增加钝化板的耐腐蚀性能,如果有需要提高钝化板耐腐蚀性能的要求,必须针对无铬钝化板研制专用的磷化液和磷化工艺。

Effect of phosphating on corrosion resistance of chromium-free passivated hot-dip galvanized sheet

The effect of the common phosphating process on the corrosion resistance and surface morphology of chromium-free passivated hot-dip galvanized sheet was studied.Scanning electron microscopy was used to analyze the samples surface morphology.At the same time,the surface morphology of the passivated plate without phosphating treatment was compared.The electrochemical anode polarization curve method and electrochemical impedance method were used to study the corrosion resistance of the passivated sheet before and after phosphating.When the weight of the passivated coating is 0.8 g/m²,the passivated film on the surface of the passivated sheet is intact after phosphating,and no rust or peeling of the passivated film is found.The electrochemical anodic polarization curve shows that the self-corrosion potential and anode current density of the passivated sheet are unchanged and the cathode current density and self-corrosion current density are increased after phosphating.The results of electrochemical AC impedance spectroscopy measurements show that the high-frequency part of the Nyquist diagram is capacitive arc before phosphating.A straight line with Warburg impedance appears after the phosphating process,which indicates that a diffusion process occurs on the surface of the passivated film after phosphating.The research results show that the surface does not form a phosphating film,and the corrosion resistance is still derived from the original passivated film of the passivated sheet by phosphateing.After the phosphating,the corrosion resistance of the passivated sheet is reduced.Therefore,the conventional phosphating treatment does not improve the corrosion resistance of the passivated sheet.If there is a need to improve the corrosion resistance of the passivated sheet,a special phosphating solution and phosphating process must be developed for the chromium-free passivated sheet.