【作者】 刘丹；

【导师】 韩恩厚； 宋影伟；

【作者基本信息】 中国科学技术大学 ， 腐蚀科学与防护， 2019， 博士

【摘要】 镁合金是最轻的金属结构材料,有着广泛的应用前景。由于镁合金耐蚀性差,服役过程中常需要使用防护涂层。然而涂层在服役过程中,一旦发生老化和破损,腐蚀将会从涂层破损处萌生,加速镁合金的失效。释放缓蚀剂的自修复涂层是解决这一问题的有效途径。虽然已经开发了多种自修复涂层,但是这些单层自修复涂层的修复能力有限,且相关修复机制尚需澄清。本文设计了一种双重自修复涂层,利用微弧氧化膜的微孔来填充成膜型缓蚀剂,并在微弧氧化膜表面有机涂层中加入与成膜型缓蚀剂协同作用的有机缓蚀剂。研究内容包括缓蚀剂的筛选,自修复涂层的制备,涂层自修复性能的检测,涂层中缓蚀剂的释放、迁移及协同修复机制。为筛选用于制备自修复涂层的缓蚀剂,研究了六种缓蚀剂对AM60镁合金的缓蚀作用。其中十二烷基苯磺酸钠(SDBS)、柠檬酸钠和2-巯基苯并噻唑(MBT)为有机吸附型缓蚀剂,Na3PO4、Ce(NO3)3和NaVO3为无机成膜型缓蚀剂。SDBS的缓蚀效率高达97%,MBT和SDBS的结构相似,能减缓阴极反应。Na3PO4的缓蚀率为94%。利用微弧氧化膜的微孔装载成膜型缓蚀剂制备自修复涂层。对比Ce(N03)3、Na3PO4和NaVO3三种高溶解度的成膜型缓蚀剂,填充Na3PO4到微孔中制得的自修复涂层性能最佳,破损后能在3.5 wt.%NaCl溶液中浸泡1周不发生明显腐蚀。该涂层的自修复能力主要源自Na3PO4在裸露基体上生成的更稳定的产物膜,同时Na3PO4溶解后对划痕附近环境的碱化也有较强的正面影响。真空浸渍使更多缓蚀剂填充到微孔内部,提高了涂层的自修复能力。但是多次浸渍并不能进一步提高涂层自修复性能。在没有缓蚀剂的情况下,微弧氧化膜的微孔是腐蚀介质的传输通道,因此微弧氧化膜自身的保护能力随微孔尺寸增大而降低。然而,当微孔中装载有缓蚀剂并在表面涂覆有机涂层后,更大的微孔能够装载更多的缓蚀剂,因此,涂层自修复能力反而有所提高。有机缓蚀剂MBT与微孔中装载的缓蚀剂Na3PO4之间具有协同作用,其源于Na3PO4对MBT溶解度的提高和MBT在产物膜缺陷区的吸附。将MBT复合到表面有机涂层制得的双重自修复涂层比单层自修复涂层具有更好的自修复能力。双重自修复涂层破损后,在腐蚀介质中,高溶解度的Na3PO4能够从划痕处裸露的微弧氧化膜中快速释放,对自修复性能起到主要作用。同时,有机涂层中释放少量MBT,吸附在自修复产物的缺陷处,进一步增强了涂层的自修复性能。MBT释放寿命较长,能有效提高涂层的长效自修复能力。研究了 AM60镁合金、微弧氧化膜和具有不同宽度划痕的复合涂层在户外暴露初期的腐蚀行为。AM60镁合金在工业大气环境中的主要腐蚀形式是开裂的腐蚀点。随着腐蚀时间延长,腐蚀点数量增多尺寸增大,腐蚀形貌逐渐由泥裂状变为更加疏松的絮状。腐蚀产物组成复杂,含有氧化镁、氢氧化镁、碳酸镁和硫酸镁。微弧氧化膜在户外暴露过程中,膜层发生部分溶解导致膜层局部脱落。作为对比,未填充缓蚀剂的复合涂层划痕内的腐蚀程度,在腐蚀介质的聚集及划痕加速作用下,比未涂装的AM60基体发生更严重的腐蚀。自修复涂层通过释放磷酸盐和MBT缓蚀剂,可减缓划痕的腐蚀。划痕较宽时,自修复涂层对划痕处仍有缓蚀作用。更多还原

【Abstract】 Magnesium alloys,as the lightest metallic structure materials,have great promising prospect.Their poor corrosion resistance makes the protection coating as a necessity in actual applications.However,once coatings are aged and damaged during service,corrosion is easy to initiate from these damaged areas,accelerating the failures of Mg parts.Self-healing coatings,which can release corrosion inhibitors,is efficient to solve this problem.Although many self-healing coatings are developed,their healing ability are highly limited and many healing mechanisms are unclear.Therefore,a duplex self-healing coating is designed in this research,which loads interphase inhibitor into the pores of micro-arc oxidation(MAO)coating and dopes an organic inhibitor which shows synergism effect with the above-mentioned interphase inhibitor into the top paint to further enhance the self-healing property.The research includes the selection of proper inhibitors,the preparation of self-healing coating,the performance of self-healing property and the study of inhibitor release/migration/synergism mechanism.To select proper inhibitor to prepare self-healing coating,the inhibition effect of 6 inhibitors on AM60 Mg alloy are studied.Among these inhibitors,SDBS(sodium dodecylbenzene sulfonate),SC(sodium citrate)and MBT(2-mercaptobenzothiazole)are organic interface inhibitor,Na3PO4,Ce(NO3)3 and NaVO3 are inorganic interphase inhibitor.The inhibition efficiency of SDBS is up to 97%.MBT,which owns similar structure with SDBS,can inhibit the cathodic reaction.The inhibition efficiency of Na3PO4 is 94%.A type of self-healing coating for AM60 Mg alloy was prepared by loading interphase inhibitor into micro-arc oxidation.Among 3 highly soluble interphase inhibitors Ce(NO3)3,Na3PO4 and NaVO3,the self-healing coating which loads Na3PO4 into MAO pores shows the best property.The exposed Mg substrate in damaged area remains un-corroded after immersion in 3.5 wt.%NaCl solution for more than one week.Its excellent self-healing property is owing to the increase of pH near the release sites of Na3PO4 and the formation of stable protection film Mg3(PO4)2.In comparison with atmospheric impregnation,vacuum impregnation can efficiently load inhibitors into MAO pores both in quantity and depth.However,more impregnation frequency cannot improve the self-healing property.Although the large size of MAO pores is harmful to the corrosion resistance of MAO coating,it is beneficial for the self-healing properties owing to the easy loading of more inhibitors.The synergism effect between organic inhibitor MBT and loaded Na3PO4 is found,and their synergism effect is attributed to the effect of Na3PO4 on the solubility of MBT and the absorption of MBT on the defects of product film.The duplex self-healing coating,which loads Na3PO4 into the pores of MAO coating and dopes MBT into the top paint,shows better healing property than the above self-healing coating.When the duplex self-healing coating is damaged,abundant highly soluble Na3PO4 is quickly released from the cross-section of scratch,and takes the main rule in self-healing process.Besides,small amount of MBT which is released from the top organic coating is absorbed in the defects of healing film,further enhancing the self-healing property.Especially,the release life of MBT is long,which prolongs the healing life of coating.The early corrosion behavior of AM60 Mg alloy,MAO coatings and self-healing coatings with different width of scratches during outdoor exposure is studied.The main corrosion morphology of AM60 is cracked corrosion point.With increasing exposure time,the corrosion points become more and larger.The main corrosion products are MgO,Mg(OH)2,MgCO3 and MgSO4.During the outdoor exposure,MAO coating is partly dissolved,leading to the local detachment of MAO coating.For the blank composite coating which mixed none inhibitor,due to the aggregation of corrosion media and the acceleration effect of scratch,the corrosion in scratch area is worse than the uncoated AM60.Self-healing coating can release Na3PO4 and MBT,inhibiting the corrosion in scratched area.When the scratch is wider,the healing property is still strong.更多还原