中文摘要：

采用磷酸盐对AZ31镁铝合金铈转化膜进行致密化处理，利用扫描电镜（SEM）、X射线光电子能谱（XPS）和电化学方法等对致密化处理之后的膜层性能进行表征，探讨转化膜致密化处理的作用机理。结果表明：转化膜经过致密化处理之后，膜表层裂纹减少，致密性得到改善，提高了对基体的覆盖度，在 NaCl 溶液中的耐腐蚀性能提高。转化膜中Ce4＋的含量减少，部分铈的氧化物/氢氧化物转变为CePO4，降低了膜层中结晶水的含量，减少了裂纹的产生与发展，提高了膜层的性能。

英文摘要：

The densification process of cerium-based conversion film on AZ31.magnesium alloy was achieved by phosphate. The properties of the film and the densification mechanism were investigated exhaustively by scanning electronic microscopy （SEM）, X-ray photoelectron spectroscopy （XPS） and electrochemical methods. The results reveal that after the post-treatment the denseness of the cerium-based conversion coatings is improved, which benefits a lot from the reduced number of cracks. As a result, the corrosion resistance of the conversion film in NaCl solution is strengthened. The less Ce4＋ ion, the transformation of hydrated cerium oxides to stable CePO4 and lower crystal water content in the films attribute to the reduce of the crack number and the improvement of the film performance.