锌铝镁镀层不同表面处理体系成分分析及耐蚀性研究

Composition Analysis and Corrosion Resistance of Different Surface Treatment Systems for Zn-Al-Mg Coating

目的分析锌铝镁镀层不同表面处理体系的成分,考察表面处理膜层的耐蚀性,明晰不同表面处理方式的防腐机制。方法通过白光干涉仪和扫描电镜(SEM)对3种表面处理方式下锌铝镁钢板不同表面微观形貌进行观察,通过辉光光谱(GDS)、X射线衍射(XRD)、X射线光电子能谱(XPS)以及傅里叶变换红外反射吸收光谱(FTIR)对表面处理膜膜层厚度及成分结构等进行表征,并结合家电板实际使用条件,考察不同钝化膜层的耐蚀性。结果涂油样品表面存在约10 nm厚、以烃类基础油和钙盐缓蚀剂等成分为主的油膜。三价铬钝化膜为厚度约50 nm,以Cr_(2)O_(3)、Cr(OH)_(3)及ZnO为主的致密不溶性氧化物膜层,无铬钝化膜为厚度约3μm、以氨基硅烷-树脂为主成膜物质的有机钝化膜。XPS及FTIR结果表明,硅烷-树脂在钢板表面发生了交联反应,形成了三维立体网状结构,同时钝化膜与镀层Zn之间形成了强化学键作用。电化学试验结果表明,三价铬钝化以及无铬钝化样品具有更小的自腐蚀电流密度及更大的电化学阻抗。在中性盐雾环境中,三价铬钝化膜具有更好的平面耐蚀性。无铬钝化膜具有更优异的划叉耐蚀性。结论三价铬钝化处理以及无铬钝化处理锌铝镁板的腐蚀倾向均小于涂油处理锌铝镁板的,相关研究可为锌铝镁镀层材料在家电板市场的推广应用提供理论支撑。

The purpose of this study is to analyze the composition of different surface treatment systems of Zn-Al-Mg coatings,investigate the corrosion resistance of surface treatment films,clarify the anti-corrosion mechanisms of different surface treatment methods,and explore the essential reasons for the difference in corrosion resistance.In this study,the surface morphologies of Zn-Al-Mg steel plates under different surface treatments were observed by white light interferometer and scanning electron microscopy(SEM).The thicknesses,element compositions and structures of surface treatment films were characterized by glow spectrometer(GDS),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared reflection and absorption spectrometer(FTIR).At the same time,the corrosion resistance of the three samples was analyzed by neutral salt spray test,Tafel test and electrochemical impedance spectroscopy(EIS).The results indicate that the anti-rust oil film was only about 10 nm thick and mainly consisted of hydrocarbon base oil and corrosion inhibitor.The anti-corrosion mechanism mainly relied on the physical adsorption of the polar head of the anti-rust agent on the surface of the coating to form a single molecule or multi-molecule adsorption layer.The adsorption layer could prevent the contact between the coating surface and oxygen and water.Cr3+passivation film was mainly composed of chromium phosphate and silica-containing organic additives(silane,etc.)with a thickness of about 50 nm.The passivation mechanism was through the dissolution of Zn on the surface to form Zn^(2+),and then the Cr3+in the solution reacted with Zn^(2+)and OH–.A dense insoluble oxide film layer mainly composed of Cr_(2)O_(3),Cr(OH)_(3)and ZnO was precipitated on the surface of the coating.A small amount of organic silicon additives in the passivation film formed a physical barrier to the corrosion factors,and then improved the corrosion resistance.Cr-free passivation film mainly adopted amino silane and water-based resin as film forming materials,which had a thickness of about 3μm.XPS and FTIR results indicated that Si-O-Si,Si-O,Si-C,Si-O-Zn,C-O and other forms existed in the passivation film,which proved that silane and resin cross-link on the surface of the steel plate formed a three-dimensional network structure.It also formed strong chemical bonds between silane and Zn-Mg-Al coating.The electrochemical tests showed that compared with the oiling treatment sample,the Cr^(3+)passivation sample and Cr-free passivation sample had smaller self-corrosion current densities and larger electrochemical impedance.In the neutral salt spray environment,compared with the chromium-free passivation film,the Cr^(3+)passivation film layer was denser,so it showed better planar corrosion resistance.The white rust area was less than 5%after 360 h.When the passivation film was destroyed,the inorganic salt corrosion inhibitor in the Cr-free passivation film re-dissolved and migrated to the damaged film layer,and reacted with the substrate to form a new oxide film.Thus,Cr-free passivation film showed better self-healing ability and more excellent scratch corrosion resistance.After 360 h,the white rust in the crossing part no longer increased.These results proved that the corrosion tendency of Zn-Al-Mg coated plates with Cr3+passivation film or Cr-free passivation film was much smaller than that with anti-rust oil film.This work provides a theoretical support for the application and popularization of Zn-Al-Mg coating materials in the home appliance board market.