硝酸镧含量对锌铝涂层组织结构和耐蚀性的影响

Effect of Lanthanum Nitrate Content on Microstructure and Corrosion Resistance of Zn-Al Coating

以稀土硝酸镧为添加剂,用硅烷钝化液代替铬酐,通过添加不量的硝酸镧制备了水性无铬锌铝涂层。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱(EDS)分析、中性盐雾试验和极化曲线等对含硝酸镧涂层试样的结构和性能进行了评价。结果表明:含5g/L硝酸镧(指其在B组分中的质量浓度)涂层试样的耐蚀性最好,适量的镧盐可以改善涂层结构,使涂层均匀致密;硝酸镧钝化处理可以显著降低涂层试样的腐蚀电流,提高腐蚀电位,抑制腐蚀速率,提高涂层的耐蚀性。硝酸镧也可以作为物理屏障,阻止腐蚀介质渗透到涂层中,但它不改变极化曲线的形状。水性无铬锌铝涂层中硝酸镧的最佳用量为5g/L。

A water-based chromium free zinc aluminum coating was prepared by using rare earth lanthanum nitrate as an additive,replacing chromic anhydride with silane passivation solution,and adding a small amount of lanthanum nitrate.The structure and properties of lanthanum nitrate coated samples were evaluated by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),neutral salt spray testing,and polarization curves.The results show that the corrosion resistance of the sample containing 5 g/L lanthanum nitrate was the best,and an appropriate amount of lanthanum nitrate could improve the coating structure and make the coating uniform and dense.Lanthanum salt passivation treatment could significantly reduce the corrosion current of coated samples,increase the corrosion potential,suppress the corrosion rate,and improve the corrosion resistance of the coating.Lanthanum salts could also serve as physical barriers to prevent corrosive media from penetrating the coating,but they did not alter the shape of the polarization curve.The optimal dosage of lanthanum nitrate in a water-based chromium free zinc aluminum coating was 5 g/L.