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以锡酸钠为转化液主要成分对Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr(GW93)镁合金进行无铬化学转化表面处理,通过全浸法评价转化膜在pH为中性的3.5%NaCl(质量分数)溶液中的腐蚀性能,利用光学显微镜、X射线衍射仪和扫描电子显微镜分析转化膜的微观形貌和相组成。结果表明,适用于GW93镁合金的锡酸盐转化膜的最佳工艺条件为:锡酸钠50 g/L,焦磷酸钠50 g/L,乙酸钠15 g/L,氢氧化钠5 g/L,柠檬酸3 g/L,碳酸钠20 g/L,转化温度80℃,转化时间15 min。转化膜主要组成为MgSnO3·3H2O。该工艺下形成的膜层为细小的、近球状颗粒堆积而成,表面均匀平整。腐蚀性能评价结果表明,未经锡酸盐化学转化的镁合金的平均腐蚀速率为6.1083 g·a-1·cm-2,经最佳化学转化成膜工艺处理后,该镁合金的平均腐蚀速率为0.1264 g·a-1·cm-2。抗腐蚀性能被提高了97.9%,说明该锡酸盐化学转化膜层可以有效地提高镁合金的耐腐蚀性能。
Chromium-free chemical conversion treatment of Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr (GW93) magnesium alloy was carried out using sodium stannate as the main component of the conversion solution, and the conversion film was evaluated at pH 3.5 % NaCl (mass fraction) solution, the microstructure and phase composition of the conversion coating were analyzed by optical microscope, X-ray diffraction and scanning electron microscopy. The results showed that the optimum conditions for stannate conversion coating for GW93 magnesium alloy were as follows: sodium stannate 50 g / L, sodium pyrophosphate 50 g / L, sodium acetate 15 g / L, sodium hydroxide 5 g / L, citric acid 3 g / L, sodium carbonate 20 g / L, transformation temperature 80 ℃, transformation time 15 min. The main composition of the conversion coating is MgSnO3 · 3H2O. The process is formed under the film is small, nearly spherical particles stacked from the surface even formation. The results of corrosion evaluation showed that the average corrosion rate of magnesium alloy without stannic acid conversion was 6.1083 g · a-1 · cm-2. After the best chemical conversion into film process, the average corrosion rate 0.1264 g · a-1 · cm-2. Corrosion resistance is increased by 97.9%, indicating that the stannate chemical conversion coating can effectively improve the corrosion resistance of magnesium alloys.