成膜时间对镁合金镧盐转化膜耐蚀性的影响

稀土盐转化膜是一种绿色环保的金属表面处理技术,为探究硝酸镧成膜时间对镁合金耐蚀性的影响,在镁合金表面成功制备出不同成膜时间下的镧盐转化膜。 试验采用扫描电镜(SEM)、能谱仪(EDS)以及 X 射线衍射仪(XRD) 对膜层的表面形貌及组成进行了表征,采用点滴试验、电化学方法(EIS / Tafel)对不同成膜时间下膜层的耐蚀性进行了测试,并使用软件对结果进行拟合。 试验结果表明,镁合金表面生成了一层微米级的稀土转化膜,转化膜表面存在裂纹,其中 30 min 成膜时间的裂纹最小;点滴试验及电化学测试结果表明镧盐转化膜能够大幅度地提高镁合金耐蚀性, 30 min 成膜时间获得的膜层耐蚀性最佳,相对于空白镁合金,其自腐蚀电流密度下降了 4 个数量级,自腐蚀电位正移了 943 mV;EDS 结果表明,膜层主要由 La 和 O 元素组成,XRD 结果进一步表明 La(OH)₃ 是膜层的主要成分。

Effects of Film-forming Time on Corrosion Resistance of Lanthanum Salt Conversion Coatings on Magnesium Alloy

Rare earth salt conversion film is a kind of green metal surface treatment technology. In order to explore the effect of lanthanum nitrate film forming time on the corrosion resistance of magnesium alloy, lanthanum salt conversion film under different film forming time was successfully prepared on the surface of magnesium alloy. Scanning electron microscopy ( SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to characterize the surface morphology and composition of the film. The corrosion resistance of the film under different film forming time was tested by the drop experiment and electro- chemical method (EIS / Tafel). The results were fitted by software. The results show that a micro scale conversion film can be formed on the surface of magnesium alloy, and there are cracks on the surface of the conversion film, among which the cracks are the smallest at 30 minutes of film forming time; the results of drop experiments and electrochemical tests show that lanthanum salt conversion film can greatly improve the corrosion resistance of magnesium alloy, and the corrosion resistance of the film at 30 mi- nutes of film forming time is the best, compared with the bare magnesium alloy, its current density has decreased by 4 orders of magnitude, and the self-corrosion potential has shifted 943mV. The results of EDS show that the film is mainly composed of La and O elements, and XRD shows that La(OH)₃ is the main component of the film.