阳极氧化及封孔处理对2024铝合金耐腐蚀性能的影响(硕士)

阳极氧化及封孔处理对2024铝合金耐腐蚀性能的影响(硕士)(论文25000字)
''摘要
2024铝合金是A1-Cu-Mg系合金，具有较高的强度和硬度，同时还具有较好的塑性等优良的性能。在某些商业民用产品和航天航空领域、交通运输等领域中都得到了广泛应用。但是2024铝合金在腐蚀介质环境中非常的敏感，很容易遭到各种腐蚀。比如：点蚀、剥蚀、晶间腐蚀和应力腐蚀等，最终导致铝合金零件的失效。
本论文以2024铝合金为基体，依托动电位极化曲线、电化学阻抗谱及等效电路的分析，研究铝合金阳极氧化膜在3.5％NaCl溶液中的耐腐蚀性能。探索了草酸二次阳极氧化法制备氧化膜的最佳一次、二次氧化时间参数。为了进一步提高其耐腐蚀性能，对阳极氧化膜进行了封孔处理，探究了植酸封孔参数对封孔效果的影响，获得了耐腐蚀性能最佳的植酸封孔处理参数。
两步阳极氧化工艺是铝合金表面形成连续附着氧化铝层以提高其耐蚀性的有效途径。通过改变第一、二次氧化时间可以获得耐腐蚀性较好的薄膜。以2024铝合金为研究对象，在草酸电解液中进行两步阳极氧化制备阳极氧化膜。随着一次氧化时间的增加，腐蚀电位先增大后减小，腐蚀电流密度先减小后增大。一次阳极氧化时间为45min时，阳极氧化膜达到优异的耐蚀性能。在一次氧化时间为45min下形成的氧化膜，经过二次阳极氧化前的去氧化层处理后得到的周期性凹坑更为优异，更有利于二次阳极氧化时氧化膜的生长。对于二次阳极氧化来说，铝合金阳极氧化膜的抗腐蚀性能随着氧化时间先变好后变差，最佳的二次阳极氧化时间为120min。氧化时间的过长，会导致膜层粗糙、疏松且易脱落，除此之外，也会使得氧化膜的溶解量增大、孔隙率增大等等，这些因素都可能会导致铝合金氧化膜抗腐蚀性能的降低。在40 g L-1草酸电解液、15℃氧化温度和40 V阳极氧化电压的前提下，以45min/120min的第一、二次氧化时间为最佳条件，具有优良的耐腐蚀性能。
植酸封孔使得铝合金草酸阳极氧化膜的耐腐蚀性能大大提高。对于铝合金草酸阳极氧化膜来说，最佳的植酸封孔工艺为植酸溶度2.5 wt.%、封孔时间15min和封孔温度90℃。未密封的铝合金阳极氧化膜呈现多孔结构。植酸封孔后的铝合金阳极氧化膜不仅填充了这些微孔，而且在其表面形成了一定厚度植酸转化膜；且植酸封孔的效果优于沸水封孔。

关键词:铝合金，二次阳极氧化，封孔处理，耐腐蚀性，电化学阻抗谱，动电位极化测试
 
Abstract
2024 aluminum alloy is A1-Cu-Mg alloywith high strength and hardness, and it also has good plasticity and other excellent properties. Therefore, it has been widely used in commercial and civil products, space aviation, transportation and many other fields. But 2024 aluminum alloy is very sensitive in the corrosive medium environment. For example, pitting, denudation, intergranular corrosion and stress corrosion can be found, which eventually lead to the failure of aluminum alloy parts.
Based on the analysis of Tafel polarization curve, electrochemical impedance spectroscopy and the simulation by equivalent circuit, the corrosion resistance of anodic oxide film formed on aluminum alloy in 3.5%NaCl solution is studied. At first, the optimum first and second oxidation times were investigated on the film by two-step anodization in oxalic acid electrolyte. In order to further improve its corrosion resistance, sealing treatment on the anodic oxide film was carried out. The influence of the sealing parameters of phytic acid was explored, and the best sealing parameters were obtained.
Two-step anodizing process can be seen as an effective way to form a continued adherent alumina layer on the surface of aluminum alloy to enhance its corrosion resistance. The film with excellent corrosion resistance can be obtained by changing the first and the second oxidation time. 2024 aluminum alloy was used as the research object, and anodic oxidation film was prepared by two-step anodization in oxalic acid electrolyte.With the increase of the first oxidation time, the corrosion potential increases and then decreases, and the corrosion current density decreases and then increases. When the first oxidation time is 45min, the anodic oxide film has excellent corrosion resistance. For the second oxidation process, the corrosion resistance of the anodic oxide film of aluminum alloy increases firstly and then decreases with the increase of oxidation time. The best second oxidation is 120min. Too long oxidation time will lead to the rough, loose and easy falling off of the oxide film. Besides, it will also increase the dissolution rate and porosity of the oxide film. All these factors may lead to the reduction of the corrosion resistance of the oxide film on the aluminum alloy.Under the premise of 40 g L-1 oxalic acid electrolyte, oxidation temperature of 15 °C, and anodic oxidation voltage of 40 V, the first/second oxidation time for 45 min/120 min was considered to be the optimum condition as it had the excellent corrosion resistance.
The corrosion resistance of the aluminum oxalic acid anodic oxide film is greatly improved by the sealing of the phytic acid. For the oxide film formed on the electrolyte of oxalic acid, the optimum technology of phytic acid sealing is the phytic acid of 2.5 wt.%, sealing timeof 15min and sealing temperatureof90 centigrade. The unsealed anodic oxide film presents a porous structure. While the sealing treatment of phytic acidnot only fills these micropores, but also forms a certain thickness of phytic acid conversion film on its surface. Moreover, for anodic oxide film formed on the electrolyte ofoxalic acid, the effect of the phytic acid sealing is better than that of boiling water sealing.

Key words:Aluminum alloy,two-step anodizing, sealing, corrosion resistance, EIS spectroscopy, potentiodynamic polarization
 
目录
第一章绪论    1
1.1前言    1
1.2 铝及其合金的腐蚀    1
1.2 铝合金阳极氧化机理    3
1.2.1 铝合金阳极氧化的原理    3
1.2.2 铝合金阳极氧化膜的结构    4
1.2.3 铝合金阳极氧化膜的性能    4
1.3 影响铝合金阳极氧化膜的因素    5
1.3.1 铝合金成分的影响    5
1.3.2 阳极氧化电压的影响    5
1.3.3 阳极氧化温度的影响    6
1.3.4 阳极氧化时间的影响    6
1.4 铝合金阳极氧化方法    6
1.5 铝合金阳极氧化膜的封孔方法    8
1.5.1 热封孔    8
1.5.2 冷封孔    9
1.5.3 中温封孔    9
1.6论文选题的意义及研究内容    10
第二章实验内容与研究方法    12
2.1实验材料和仪器设备    12
2.2 铝合金阳极氧化膜的制备    13
2.2.1 预处理过程    13
2.2.2 阳极氧化过程    14
2.2.3 封孔处理过程    14
2.3 阳极氧化膜的性能测试    15
2.3.1 氧化膜的形貌分析    15
2.3.2 电化学性能测试    15
2.4 本章小结    16
第三章二次阳极氧化对2024铝合金耐腐蚀性能的影响    17
3.1 前言    17
3.2 一次阳极氧化时间对铝合金耐腐蚀性能的影响    17
3.2.1动电位极化测试    17
3.2.2电化学交流阻抗测试    18
3.3 二次阳极氧化时间对铝合金耐腐蚀性能的影响    19
3.3.1动电位极化测试    19
3.3.2电化学交流阻抗测试    20
3.4 本章小结    21
第四章植酸封孔工艺对阳极氧化膜腐蚀行为的影响    22
4.1 前言    22
4.2 实验方法    22
4.3 表面形貌分析    23
4.4 动电位极化分析    23
4.5 交流阻抗谱分析    25
4.6 本章小结    27
第五章总结与展望    29
5.1 本文总结    29
5.2 未来展望    29
参考文献    30
致谢    35