GW93镁合金表面锡酸盐化学转化膜工艺研究

Stannate Chemical Conversion Coating on the Surface of GW93 Magnesium Alloy

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。

A chrome-free chemical conversion process using sodium stannate as the main component was investigated for corrosion protection of Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr magnesium alloy （GW93）. Corrosion property of the specimens with and without chemical conversion film was evaluated by full immersion test in neutral 3.5wt% NaCl solution. The microstructure and phase composition of the chemical conversion film were analyzed by optical microscope, X-ray diffraction meter and scanning electron microscope. The results show that the optimum chemical conversion processing for GW93 magnesium alloy is Na2SnO3 50 g/L, Na4P2O7 50 g/L, NaOH 5 g/L, CHaCOONa 15 g/L, citric acid 3 g/L and sodium carbonate 20 g/L at 80 ℃ for 15 rain. Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr is covered by uniform chemical conversion coating composed of MgSnOH-3H2O. The immersion test shows that the average corrosion rate of the specimen without chemical conversion treatment is 6.1083g·a^-1·cm^-2, and that of the specimens with chemical conversion treatment is 0.1264 g·a^-1·cm^-2. Corrosion resistance is improved by 97.9%, which suggests that stannate chemical conversion treatment could provide effective corrosion protection for GW93 magnesium alloy.