Hot dip galvanized (HDG) coatings are widely used in various industrial fields for better corrosion protection of steels. Comparative study of the corrosion behavior of the phosphated hot-dip galvanized steel conversion coatings and post-sealing in sodium silicate solution were characterized in 3.5 % NaCl solution by different techniques, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The surface morphology and elemental composition of hot-dip galvanized steel and post treated were characterized by scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that after phosphating the porous phosphate crystals formed on the surface of HDG steel and the phosphating followed by post-sealing samples in sodium silicate solution filled into the phosphate pores. The optimum silicate concentration ranged from (3-5 g/l), its morphology has fine crystal, compacted and dense uniform coating (zinc-silicate complex). Low silicate concentration (3-5 g/l) have better protection property and best corrosion performance than other high concentration (7-10 g/l) due to cracks formation in coating and bad protection.
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机译：热浸镀锌（HDG）涂层广泛用于各种工业领域，以更好地保护钢。在3.5％NaCl溶液中，采用不同的技术，电化学阻抗谱（EIS）和电势极化，对磷酸盐化的热浸镀锌钢转化涂层的腐蚀行为和在硅酸钠溶液中的后密封的腐蚀行为进行了比较研究。通过扫描电子显微镜（SEM）和能量色散X射线光谱仪（EDX）对热浸镀锌钢的表面形态和元素组成进行了后处理。结果表明，磷化后，在HDG钢表面形成的多孔磷酸盐晶体发生磷化，然后在填充到磷酸盐孔中的硅酸钠溶液中进行后密封样品。最佳硅酸盐浓度范围为（3-5 g / l），其形态具有细小的晶体，致密且致密的均匀涂层（锌硅酸盐络合物）。与其他高浓度硅酸盐（7-10 g / l）相比，低硅酸盐浓度（3-5 g / l）具有更好的防护性能和最佳的腐蚀性能，这是由于涂层中形成了裂纹并且保护性差。
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