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

摘要:

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。

Abstract:

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, CH3COONa 15 g/L, citric acid 3 g/L and sodium carbonate 20 g/L at 80 oC for 15 min. Mg-8.8Gd-3.1Y-0.6Zn-0.5Zr is covered by uniform chemical conversion coating composed of MgSnO3·3H2O. The immersion test shows that the average corrosion rate of the specimen without chemical conversion treatment is 6.1083 g·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.