摘要镁合金是我们生活中常用的一种合金，但是在镁合金的实际运用中却遇到了很多 问题，镁合金不稳定，耐蚀性能差容易发生腐蚀，所以在镁合金的表面添加一层具有 抗腐蚀的膜层对于镁合金的运用有着重要作用。81108

本文运用化学转化法给镁合金表面添加一层锡酸盐转化膜，来提高镁合金的耐蚀 性。以 AZ91D 镁合金作为实验材料，用草酸、磷酸、酒石酸和柠檬酸分别对镁合金 进行酸洗从而寻找到最佳的酸洗方案。以锡酸钠、焦磷酸钠和乙酸钠作为转化液的主 要成分，对镁合金进行转化处理，后采用正交实验的方法确定了最佳的成膜工艺，用 单一变量实验确定了锡酸钠的含量对膜层耐蚀性的影响程度。同时也用硫酸铜点滴实 验观察了膜层耐蚀性能的强弱。也用到了电化学实验法验证了转化膜的耐蚀性。通过 XRD、SEM 和 EDS 图对膜层进行了分析，初步探讨了锡酸盐转化膜的成膜机理。

酸洗结果可以看出草酸溶液对镁合金的酸洗效果最好，溶液的浓度应控制在 25g/l 左右。正交实验以及控制单一变量的实验得到最佳的转化工艺为：锡酸钠 45g/l、 焦磷酸钠 35g/l、乙酸钠 6g/l、NaOH 12g/l。其中锡酸钠对膜层性能影响较为明显。电 化学实验结果可以看出锡酸盐转化膜一定程度的提高了镁合金的耐蚀性，但膜层的耐 蚀性能不太理想。XRD、SEM 和 EDS 图像看出转化膜为一层白色球状颗粒紧密的排 列在镁合金表面，转化膜的主要成分为 Mg(OH)2、MgSn(OH)6。

毕业论文关键词：AZ91D 镁合金；锡酸盐；转化膜；耐蚀性

Abstract Magnesium alloy is commonly used in our daily lives, however，the practical application of magnesium alloy has encountered a lot of trouble, magnesium alloy is unstable, prone to poor corrosion resistance to corrosion, so we added a layer of anti corrosion coating to the the surface of the magnesium alloy for the use of magnesium alloy。

In this paper,we used a chemical conversion method to add a layer of magnesium alloy surface stannate conversion coating to improve the corrosion resistance of magnesium alloy。We also used AZ91D magnesium alloy as experimental material,and we added oxalic acid,phosphoric acid, tartaric acid and citric acid, respectively in order to find the best pickling conditions。 sodium pyrophosphate and sodium acetate were used as the main component transformation solution of magnesium alloy conversion process, after finding out the coating process with a single variable determined and its infulence to the optimum film coating process with a single variable determined experiment。We observed the copper sulfate spot to test the strength of film corrosion resistance。We also used the electrochemical experiment to verify the corrosion resistance of the conversion coating。By XRD, SEM and EDS analysis diagram of the film was preliminarily discussed forming mechanism stannate conversion film。

We can see from the pickling results that oxalic acid solution is the best way to effect the magnesium alloy, the concentration of the solution should be controlled at 25g/l or so。 Control of a single variable and orthogonal experiment to get the best conversion process: tin sodium 45g/l, sodium pyrophosphate 35g/l, sodium acetate 6g/l, NaOH 12g/l。 It's obvious that sodium stannate has the most impact on the performance of the film。The electrochemical experimental results can be seen to some extent that the stannate conversion coating improves the corrosion resistance of magnesium alloy, but corrosion resistance of the film is not ideal。We can see form the XRD, SEM and EDS images that conversion coating is a layer of white spherical particles arranged in magnesium alloy conversion。 Conversion coating is mainly composed of Mg (OH) 2, MgSn (OH) 6。

Key words： AZ91D magnesium alloy；stannate；conversion coating；corrosion resistance