AZ91镁合金表面稀土转化膜的制备及耐蚀性能研究

采用在镁合金表面形成无毒、无污染的稀土铈转化膜的方法解决AZ91镁合金表面的腐蚀问题。确定了最佳成膜工艺参数，讨论了处理液的浓度、成膜温度和成膜时间等因素对转化膜耐蚀性的影响。利用湿热实验、阳极极化曲线的测定等实验方法评价了转化膜对镁合金表面的防护作用。结果表明，在潮湿温热条件下稀土铈转化膜试样仍能保持膜层的完整性并具有较高的覆盖度，腐蚀现象不明显。腐蚀电势升高，出现钝化现象，腐蚀电流密度下降，稀土铈转化膜可以提高AZ91镁合金的耐蚀性能。用扫描电镜观察了膜的微观形貌，稀土铈转化膜是由基膜和附着的细小颗粒组成，最佳工艺形成的铈转化膜无破碎现象，对AZ91镁合金表面的腐蚀过程的发生有明显的抑制作用。

Preparation and Corrosion Resistance of Rare Earth Conversion Coatings on AZ91 Magnesium Alloy

The feasibility of forming Ce-containing rare earth conversion coating (short for RECCs), which is nonpoisonous and green to the environment, onto the AZ91 magnesium alloy surface in order to increase the corrosion resistance was studied. And the optimum technological conditions, such as the appropriate concentrations of the components in the solution, temperature and duration of the coatings formation were also settled. The protection of conversion coatings on magnesium alloy surface was evaluated by moisture/heating test, anodic polarization, etc. The results show that the corrosion resistance of AZ91 magnesium alloy covered by RECCs is improved. And the coatings are complete and have high coverage and anti-corrosion under moisture/heating condition. The corrosion potential increased and passive phenomenon exists while the current density decreases. The morphology of Ce-containing RECCs is found to be a few particles coherent to a base coating by SEM. The RECCs formed under the optimum technological conditions have no cracks and exhibit apparent corrosion resistance.