【作者】 刘浩泉；

【导师】 王昕；

【作者基本信息】 中国海洋大学 ， 材料学， 2010， 硕士

【摘要】 本文对铝及其合金表面稀土转化膜的制备工艺进行了初步研究,探讨了化学沉积转化膜的成膜机制和膜层裂纹的产生机理；以减少转化膜表面裂纹和改善其耐腐蚀性为目的,开发了磷酸盐后处理工艺,并对后处理的原理进行了研究。本文主要采取了以下的表征方法：利用扫描电子显微镜(SEM)、能谱仪(EDS)和涂层测厚仪来研究稀土转化膜的微观组织形貌、表面元素组成和膜厚；电化学阻抗谱、极化曲线和全浸腐蚀实验研究了试样表面稀土转化膜的电化学腐蚀行为和耐蚀机理。利用正交实验确定了化学沉积成膜的最佳工艺参数。通过分析化学沉积过程中的膜层厚度、膜层单位面积质量、表面微观形貌和表面元素组成随沉积时间的关系,进一步研究了不同成膜工艺参数(稀土盐浓度、高氯酸钠的浓度、氧化剂过氧化氢的浓度、成膜时间和溶液的pH值)对稀土转化膜的影响。提出了化学沉积过程转化膜的成膜和裂纹形成机理：首先在溶液中发生的是铝的氧化和过氧化氢的还原过程,之后随着氢氧根离子的增多,靠近试样表面的溶液pH值逐渐升高,通过一系列反应最终形成了氧化铈转化膜,最后由于膜层的脱水会导致膜层开裂。采用正交实验优化了化学沉积转化膜的磷酸盐后处理工艺,分析了不同后处理工艺参数(磷酸钠浓度、溶液温度、pH值和反应时间)对最终成膜的影响。实验结果表明,化学沉积稀土转化膜在经过磷酸盐后处理后,通过物质的转化形成了新的磷酸铈水合物,膜层的抗开裂性和耐蚀性能获得了很大的提高。更多还原

【Abstract】 This thesis is aimed at the preparation technology of REM (rare earth metal) conversion coating on the aluminum and its alloy. The mechanism of the growth of spontaneous deposited conversion coatings and the formation of cracks on the surface of the coatings were discussed. For purpose of reducing the cracks on the conversion films and improve the corrosion resistance of these films, phosphate post-treatment process was developed. The theory of the post-treatment was studied. In this paper, characterization methods used mainly included:The microstructure, element composition and thickness have been examined by scanning electron microscopy (SEM), energy spectrometer (EDS) and coating thickness gauge. The corrosion behavior and corrosion mechanism of the substrate with conversion coating were evaluated by polarization curves, electrochemical impedance spectroscopy (EIS) and corrosion test.The technical parameter of spontaneous deposited conversion coating was optimized by orthogonal tests. The analysis on the relationship between the thickness, mass per unit area, the micro-morphology, the element composition of the conversion coatings and the deposited time, further research on the effects of technical parameters (concentrations of rare earth salts, concentrations of sodium perchlorate, concentrations of oxidizer H2O2, immersion time and pH value of solution). The spontaneous depositing process theory about the formation of conversion films and crack initiation was proposed. At first, the deposition mechanism involves both the oxidation of aluminum and the reduction of hydrogen peroxide in the reactions. Then, the generation of hydroxide ions results in a pH increased near the surface of the substrate, which causes the formation of cerium oxide conversion coating by a series of reactions. At last, after the formation of the film, some cracks induced by dehydration of the coating will appear.The optimum technical parameter of phosphate post-treatment was obtained by orthogonal tests. The effects of technical parameters (concentrations of sodium phosphate, temperature, treating time and pH value of solution) in post-treatment process were studied in detail. The experimental results showed that after spontaneous deposited Rare Earth conversion coating was post-processed, converted the structure of deposited coatings into hydrated cerium phosphate structure, the number of cracks was reduced and corrosion resistance was improved a lot.更多还原