【作者】 刘建才；

【导师】 张新明； 陈明安；

【作者基本信息】 中南大学 ， 材料加工工程， 2011， 博士

【摘要】 高比电容电解电容器用铝箔是一种高技术和高附加值产品,它是电子工业最基本的元器件——电容器的基础材料。国内某厂现有高压箔产品在铬酸体系下发孔效果较好,比电容高；但在环保型硫酸体系工艺条件下,出现发孔腐蚀不均匀,发孔数量少等问题,导致化成后表面积小,静电容量不高。因此,为了提高铝箔的发孔率及发孔均匀性,开发适合硫酸体系的高压箔生产技术和产品,本文利用金相显微镜(OM)、X-射线织构仪、扫描电镜(SEM)、二次离子质谱(SIMS)和电化学工作站等检测分析手段和技术平台,对高纯铝箔组织和再结晶织构的演变规律进行了研究,结合第一原理模拟技术,研究了热处理、表面处理和痕量元素含量及分布对铝箔腐蚀发孔性能的影响规律,得到以下结论：(1)利用第一原理模拟技术,揭示了痕量元素在铝合金中的分布规律；利用空位迁移原理,建立了痕量元素表面偏析的动力学模型；首次建立了痕量元素种类和含量作用于铝合金表面化学势和溶解电极电势的直接关系式,揭示了痕量元素对铝合金表面电化学性质的影响机理。理论计算结果为高压铝箔成分的设计提供指导。(2)揭示了最终退火工艺对铝箔的立方织构占有率、微观组织和铝箔腐蚀发孔率及发孔均匀性的影响规律。结果表明：采用适当速度升温,高温退火后快冷可使铝箔中的痕量元素富集在铝箔表面并保持相对分布均匀的状态,使得腐蚀发孔均匀,腐蚀性能得到提高。(3)确定了使铝箔形貌状态均匀并提高发孔均匀性的表面清洗工艺技术。在发孔前用碱清洗铝箔表面可以使铝箔表面的氧化膜溶解变薄,酸清洗则将Cl-引入铝箔表面,酸碱清洗共同使铝箔的腐蚀电位降低,腐蚀电流增大,促进铝箔的腐蚀发孔,提高发孔率,增加发孔均匀性。(4)揭示了痕量元素In影响高纯铝形变组织及宏观冷轧织构的形成和演变规律,及其对再结晶立方织构的影响规律。实验发现In可细化铝箔组织,添加In含量在40ppm以内对铝箔立方织构的形成有利。In含量在40ppm时,铝箔经高温短时退火后立方织构取向密度最大,继续增加In含量立方取向密度反而下降。(5)探明了痕量元素In含量和分布、最终退火工艺和表面清洗工艺对铝箔腐蚀发孔性能的影响规律,并探讨了其影响机理。In为大尺寸的原子,通过控制不同的热处理条件可以调整和控制痕量元素In在铝箔表面的富集和存在状态。痕量元素In对铝箔的腐蚀机制与Pb相似,迁移到铝箔表面的In原子主要富集在铝箔基体与氧化膜界面处。由于In有比Al更正的电位,In与Al原子形成局部微电池,提高铝箔表面的活性,进而显著提高铝箔的腐蚀效率、增加腐蚀发孔面积,使腐蚀孔坑分布均匀。(6)建立了铸锭无均匀化退火直接制备高立方织构含量和优异腐蚀发孔性能的高压铝箔的技术,以及添加ppm级痕量元素的技术。利用三层法高纯铝和偏析法高纯铝包含不同痕量元素的优点,混合使用通过特定的制备工艺可以确保高压箔的立方织构比例高于95%,腐蚀发孔率在98%以上,蚀坑分布均匀。该技术不但省掉了铸锭均匀化退火工艺,还将痕量ppm级的对铝箔腐蚀发孔有利的元素如Ga等直接加入铝箔中,减少了熔铸时添加痕量元素中间合金的麻烦,即节约能耗又提高了生产效率和经济效益。更多还原

【Abstract】 The electrolytic capacitor aluminum foil with high specific capacitance is a high-tech and high value-added product. It is the main material for capacitors which are the basic devices of the electronic industry. The domestic aluminum foil has high corrosion capacitance in the chromic acid system, but uneven pitting and few etching pits are produced in the environmental of H2SO4 corrosion system, which result in small surface area and low capacitance after forming and etching. In order to promote pitting ability and corrosion homogeneities of aluminum foils, the microstructure and recrystallization texture evolution of high voltage aluminum foils have been investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), secondary ion mass spectrometer (SIMS), electrochemical technique. Combined with first principle simulation, the influence of heat treatment, surface treatment and the amount and distribution of trace elements on the homogeneity of etching pit has been studied. The main conclusions are as following:(1)The distribution of trace elements in pure aluminum was investigated by first principle simulation. According to the vacancy transportation principle, a model was established to describe the kinetics process of segregation of trace elements on clean surface via atomic movement through vacancies. The effect of doped trace elements on the electrochemical properties of aluminum surface was investigated, and a straightforward equation was suggested to desbribe the surface chemical potentials of metals and the electrochemical dissolution potentials of alloy surfaces. The calculation results provide a reference for the future design of high voltage aluminum foils.(2) The effect of heat treatment on the volume fraction of cube texture, microstructure and the pitting ability was studied. The results indicated that properiety speed of heating-up and rapid cooling at the elevated temperatures led to homogeneous dispersion of trace elements on aluminum foil surface and more corrosion pits that ensure high specific capacitance.(3) The surface treatment was used to improve the uniformity of pitting on the surface of the aluminum foils. The sodium hydroxide pre-treatment before pitting can remove the oxide film on the foils, and the hydrochloric acid pre-treatment can introduce Cl-ion into the surface of foils. NaOH+HCl co-pre-treatment reduces the corrosion potential and increases the corrosion current density. The area and density of the pit etching on the surface were promoted after pre-treatment, and the uniformity of pitting was also improved significantly.(4) The effects of In trace element on the deformation microstructure, the evolution of cold rolling texture and recrystallization texture of the high purity aluminum foils were investigated. The results demonstrated that In element can refine the grains of the aluminum foils and ensure the percentage of recrystallization cube texture in the aluminum foils higher than 95%.(5) The influence of the content and distribution of trace In, the final annealing and surface treatment on the homogeneity of etching pit has been investigated, and the mechanism was explored. The enrichment and the distribution of trace element In on the foil surface can be adjusted by carefully controlling the heat-treatment parameters. The mechanism of pitting behavior of trace In on aluminum surface was similar to that of Pb. Most of the enriched In was found to be near the oxide film/aluminum matrix interface. Since the potential of In is much higher than that of aluminum, a local electrochemical cell was formed between In and Al substrate. Thus the efficiency of corrosion was improved and the etched area became larger. The corrosion pits of the etched aluminum foil became more uniform.(6) A new method without homogenizing treatment of ingot was established to fabricate high voltage aluminum foils with high content of cube texture and excellent pitting corrosion properties. Taking advantage of three-layer-electrolysis high-purity aluminum and partial high-purity aluminum, more than 95%volume fraction of cube texture and 98% corrosion region distributed well can be obtained through special designed process. Moreover, it introduced the gallium into aluminum foils directly. It has the advantages of lower cost, higher efficiency and more economy benefits.更多还原