镁合金表面磷酸盐-高锰酸盐转化膜的制备与耐蚀性能

Preparation and Corrosion Resistance of Phosphate-permanganate Conversion Coating on Surface of Magnesium Alloy

目的在镁合金表面制备磷酸盐-高锰酸盐化学转化膜,以提高镁合金的耐蚀性能。方法以磷酸盐与高锰酸盐为转化处理液,在镁合金表面制备出化学转化膜,进而采用SEM、EDAX、XRD及电化学测试方法研究了转化温度、转化液p H值和转化时间对转化膜形貌、成分、厚度、结构和耐蚀性的影响。结果磷酸盐-高锰酸盐转化膜呈深紫色,由Mg、P、Mn和O元素组成,膜层表面存在网状裂纹,厚度为4~18μm,转化膜的耐蚀性随转化温度、p H值、转化时间的增加呈现先增加后降低的变化规律。结论磷酸盐-高锰酸盐转化膜由镁的磷酸盐组成。磷酸盐-高锰酸盐转化处理的最佳工艺条件为：转化温度40℃,转化液p H=3.5和转化时间15 min。经磷酸盐-高锰酸盐化学转化处理后,镁合金的耐蚀性能得到了明显的提高。

The work aims to improve the corrosion resistance of magnesium alloy by preparing phosphate-permanganate conversion coating on the surface of magnesium alloy. The chemical conversion coating on the surface of magnesium alloy was prepared with phosphate-permanganate as conversion electrolyte. Effects of conversion temperature, p H value and conversion time on the surface morphology, chemical composition, thickness, structure and corrosion resistance of the conversion coating were studied by scanning electron microscopy（SEM）, energy dispersion analyzer of X-ray（EDAX）, X-ray diffraction（XRD） and electrochemical test. The phosphate-permanganate conversion coating was dark violet and 4~18 μm thick. It consisted ofMg, P, Mn and O elements with purple appearance and micro cracks. The corrosion resistance of conversion coating first increased and then decreased as the conversion temperature, p H value and conversion time increased. The phosphate- permanganate conversion coating is composed of magnesium phosphate. Optimum processing conditions are as follows： conversion temperature of 40 ℃, p H value of 3.5 and conversion time of 20 min. After chemical conversion treatment by phosphate-permanganate conversion electrolyte, the corrosion resistance of magnesium alloy is greatly improved.