AZ91D镁合金上钼改性锌系磷化膜的制备、结构及性能

Preparation,Structure and Properties of Molybdate Modified Zinc Phosphate Coating on Magnesium Alloy AZ91D

采用在磷化液中添加钼酸钠及腐蚀抑制剂的方法,在AZ91D镁合金表面上制备了均匀细致的锌系复合磷化膜.用XRD对膜层的化学组成及结构进行了表征,用SEM和EDS对膜层的形貌和组分含量进行分析.结果表明,磷化膜主要由Zn3(PO4)2.4H2O和单质Zn组成.在磷化液中加入钼酸钠使磷化膜组织更加细致而且无裂纹.磷化液中的钼酸钠含量为1.5 g/L时,磷化膜的结晶最致密,单质锌的含量最高,耐蚀性最好.还提出了一种快速测量镁合金表面膜层耐蚀性的试验方法,同时对镁合金上的磷化反应的机理进行了探讨.

Uniform and dense molybdate modified zinc phosphate coatings were formed on the magnesium alloy AZ91 D surfaces by using a phosphating bath containing molybdtate and corrosion inhibitor. Phase components of coatings were analyzed by XRD. Morphology and compositions of coatings were analyzed by SEM and EDS. The results indicate that the phosphate coatings consist mainly of Zn3（PO4）2·4H2O and Zn. When molybdate was added in the bath, phosphate coatings became denser and crack-free. The phosphate coatings obtained from the bath containing 1.5 g/L sodium molybdate exhibit denser microstructure and higher concentration of metallic zinc. A corrosion test estimating the corrosion resistance of conversion coating on magnesium alloy was proposed. Phosphating reaction mechanism on the magnesium alloy AZ91 D surfaces was also investigated.