热浸镀Galfan表面镧盐转化膜的生长和耐腐蚀性能的研究

Preparation and Corrosion Performance of Lanthanum Nitrate Conversion Coating on Hot-dip Galfan Steel

在热浸镀Galfan镀层表面制备了镧盐转化膜,采用扫描电镜及能谱分析(SEM/EDS)、X射线光电子能谱分析(XPS)、原子力扫描探针显微分析(AFM)研究镧盐转化膜的表面形貌、化学成分和结构。通过中性盐雾试验、电化学极化分析和电化学阻抗研究膜层的耐腐蚀性能,确定最佳成膜时间。结果表明:镧盐转化膜成膜不均匀,优先在晶界或相界等活性区域;随着处理时间的延长,膜层的厚度增加;膜层上存在裂纹,且裂纹随着处理时间的延长而变宽,处理时间超过30 min时,膜层脱落,耐腐蚀性能降低;镧盐转化膜由La的氧化物/氢氧化物以及少量的Al和Zn的氧化物/氢氧化物组成。与未经处理的热浸镀Galfan镀层相比,镧盐转化膜显著减低基体的腐蚀速率,明显提高其耐腐蚀性能。

Lanthanum nitrate conversion coating was prepared on a hot-dip Galfan steel by dipping in a passivation solution of La（NO3）3. The surface morphology, chemical composition and structure of the coating were characterized by scanning electron microscopy（SEM） with X- ray energy dispersive spectrometer（EDS）, X-ray photoelectron spectroscopy（XPS） and atomic force microscope（AFM）. The corrosion resistance of the conversion film coated steel was assessed by neutral salt spray tests（NSS）, electrochemical polarization curve and electrochemical impedance spectroscopy（EIS）. The results showed that the conversion coating was not uniform, which had grown preferentially on grain- and phase-boundaries as well as other active sites. The thickness of the coating increased, while cracks in the coating expanded gradually with the increasing dipping- time. The coating spall off after dipping for more than 30 min, and therewith the protective performance of the coating degraded. In comparison with the blank Galfan steel, the corrosion rate of the conversion film coated Galfan steel lowered down significantly.