【作者】 刘渝萍；

【导师】 张丁非；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2011， 博士

【摘要】 针对含氟、铬、磷镁合金阳极氧化液的污染问题和阳极氧化工艺不易控制的问题,本文以AZ31镁合金为研究对象,开发了环境友好型AZ31镁合金阳极氧化电解液配方及工艺,从半导体电化学理论为基础讨论了镁合金阳极氧化的成膜机制,最后考察了镁合金阳极氧化膜的腐蚀性能与电偶腐蚀行为,这将有助于促进镁合金的广泛实际应用。经过大量试验,开发了环境友好型镁合金阳极氧化电解液配方及工艺,电解液由氢氧化钠、硅酸钠、植酸、聚天冬氨酸（PASP）组成。优化工艺下,AZ31镁合金阳极氧化膜具有灰白色、多孔状、裂纹状特点,由MgO和Mg₂SiO₄组成。作为环境友好型除垢剂,聚天冬氨酸较少用于镁合金阳极氧化的有机添加剂。当PASP浓度从0g/L到28.8g/L时,AZ31镁合金阳极氧化膜的槽压、膜生长速度、组分含量明显提高,但当PASP浓度大于28.8/L时,反而抑制氧化膜生长。提出了“吸附构型转变”机制,并用量子化学计算解释了PASP浓度对AZ31镁合金阳极氧化膜生长的作用行为,即“站立式吸附”和“平躺式吸附”之间的转变。热力学计算发现镁合金阳极氧化液中氢氧化物和硅酸盐的浓度将很大程度决定氧化膜的种类。从成膜现象和厚度变化来看,AZ31镁合金阳极氧化膜生长符合“抛物线规律”。从结构和成分变化来看,氧化膜主要有多孔层和冶金层组成,并且氧化膜中MgO和Mg₂SiO₄的物质量不断增加,膜外层以Mg₂SiO₄为主,膜内层以MgO为主,说明阳极氧化初期,氧化膜以外延生长为主,受界面电化学反应控制;阳极氧化中后期,氧化膜以内延生长为主,受扩散速度控制。从表面形貌和断面形貌来看,表面微孔不断减小,断面孔洞越来越大。最后,在半导体电化学理论和PMD模型基础上,提出了有关“能带模型”和“缺陷模型”的电化学成膜机制。AZ31镁合金及其阳极氧化膜在阳极氧化液中能带发生弯曲是发生火花放电的重要原因。AZ31镁合金阳极氧化膜的生长是氧离子空位迁移而形成,镁合金的溶解是由于镁离子空位扩散的净结果。采用半导体电化学技术,建立了AZ31镁合金阳极氧化成膜因素与半导体特性有关联性。在3.5%NaCl溶液中,氧化膜呈n型半导体。随着氧化时间的增加,载流子密度逐渐减小,平带电位变负,半导体特性减弱;随着电流密度的增加,载流子密度几乎逐渐增大,平带电位几乎变正,半导体特性减弱;随着温度的升高,载流子密度几乎逐渐增大,平带电位几乎变正,半导体特性略减。当阳极氧化条件为20min、10mA/cm²、20℃时,AZ31镁合金阳极氧化膜表现出较强的半导体特性和耐腐蚀性能。最后,采用电化学技术和全浸实验,得出AZ31镁合金阳极氧化膜比空白镁合金的耐腐蚀性能明显提高,以及封孔的AZ31镁合金阳极氧化膜与有机涂层处理的铝合金、低碳钢之间的电偶腐蚀效应明显降低。更多还原

【Abstract】 For these issues of the pollution problem of anodizing electrolyte including F, Cr and P and the difficulty of controlling the process conditions, this paper developed the environment-friendly anodizing oxidation electrolyte and process based on magnesium alloy of AZ31.With the theory of semiconductor electrochemistry, the formation mechanism of AZ31 was discussed and evaluated the corrosion performance and galvanic corrosion behavior of the anodic film formed on AZ31.This research will be promote the practical applications.After a lot of trial, a kind of environment-friendly anodizing oxidation electrolyte and process was developed. And the electrolyte consists of NaOH, Na₂SiO₃,Phytic acid and sodium of polyaspartic acid（PASP）.With the optimal process, the anodic film with micro-cracks was grey white and porous. And the composition of the anodic film is MgO and Mg₂SiO₄.As a scale inhibitor, PASP barely is used in anodizing magnesium alloy as the organic agent. With the regime of PASP from 0g/L to 28.8g/L, the cell voltage, the formation rate and the content of the constituents were improved obviously. But over 28.8g/L, PASP decreased the development of the anodic film. Thus, a plausible model we propose that the anodizing process is regulated by two main plausible adsorption orientations of PASP at the surface anode. Furthermore, the quantum chemistry calculation was adopted to explain this model including flat-on configuration and end-on configuration.From the thermodynamic analysis, the constituent was decided on the concentration of NaOH, Na₂SiO₃ in anodizing electrolyte. From the experimental phenomenon and the variation of the thickness, there were three stages in anodizing process and the growth curve was in keeping with the tendency of parabolic curve. With the structure and composition test, the anodic film has two layers of porous lay and metallurgical coating. And the amount of substance of MgO and Mg₂SiO₄ was increased. Mg₂SiO₄ was the main constituent in outer coating and MgO was the main constituent in inner coating. These results implied that in the initial stage, the anodic film was formed with epitaxial growth with the control of electrochemistry reaction and in the later stage, the anodic film was formed with topotaxy with the control of diffusion process. From the surface and cross-sectional morphologies, the dimension of micro-pore became smaller and the dimension of cavities became larger. Finally, based on the semi-conductor electrochemical theory and PMD model, the electrochemical mechanism about energy band model and defect model was proposed. The bending of energy band of Mg alloy in anodizing electrolyte is very important reason for the discharge of sparks. The anodic film formed on AZ31 originated from the migration of Oxygen ion vacancy and the dissolution of Mg alloy originated from the Magnesium ion vacancy.We have used semiconductor electrochemistry technique, a correlation of the formation conditions and semiconductor properties was established. In 3.5% NaCl solution, the anodic film formed on AZ31 was n-semiconductor. With the increasing of anodizing time, the carrier concentration decreased gradually and the flat band potential shifted to the negative direction, while the characteristics of the semiconductor declined. With the increasing of current density and temperature, the carrier concentration almost increased and the flat band potential almost shifted to the positive direction, while the characteristics of the semiconductor declined. The anodic coating formed on AZ31 showed stronger semiconductor characteristics and good corrosion performance.Finally, using electrochemical technique and immersion experiment, the corrosion performance of the anodic film was better than that of Mg ally AZ31.And the galvanic effect of the sealed anodic film and the aluminium alloy and low-carbon steel treated with organic coating declined evidently.更多还原