【作者】 苗景国；

【导师】 吴润；

【作者基本信息】 武汉科技大学 ， 材料学， 2013， 博士

【摘要】 铝及其合金具有质轻、比强度高、韧性好及易加工等优点，但其硬度低及耐磨性差等缺点又限制了它的应用。在铝及其合金表面施以陶瓷化技术可以赋予其表面拥有特殊的优良性能。微弧氧化技术是近年来兴起的在铝、镁、钛及其合金表面进行处理的新工艺。通过微弧放电在铝及其合金表面原位生长出一层陶瓷质膜层，该膜层具有硬度高、耐磨性好、与基体结合力好等优点，在机械、电子、纺织、航空航天等领域具有广泛的应用。影响铝合金微弧氧化陶瓷层性能的因素主要有：电解液参数、电参数以及基体材料中的合金元素等。本文采用正交实验法，优化出了7075铝合金在铝酸钠、硅酸钠、硼酸钠和磷酸钠四个电解液体系下进行微弧氧化的最优配方；在最优配方的基础上，采用单因素分析法，以陶瓷层厚度、显微硬度及微观形貌作为实验指标，对电流密度、占空比、频率及氧化时间等电参数依次进行了优化；并对在不同氧化时间条件下制备出的陶瓷层的耐蚀性、耐磨性及力学性能进行了表征，对基体材料中合金元素在微弧氧化过程中的影响也进行了相应的探究。实验过程中得出的结论如下：采用正交实验法，优化出了7075铝合金分别在铝酸钠、硅酸钠、硼酸钠、磷酸钠电解液体系下进行微弧氧化的最优配方为：铝酸钠体系：铝酸钠9g/L，氢氧化钠1g/L，三乙醇胺6ml/L硅酸钠体系：硅酸钠8g/L，氢氧化钠1g/L，三乙醇胺6ml/L硼酸钠体系：硼酸钠15g/L，氢氧化钠1g/L，三乙醇胺6ml/L磷酸钠体系：磷酸钠12g/L，氢氧化钠1g/L，三乙醇胺6ml/L对四体系下制得的陶瓷膜层进行厚度、硬度、表面及截面形貌表征，综合考虑，在铝酸钠体系下制得的陶瓷膜层质量最好。故选用优化出的铝酸钠体系，采用单因素分析法，详细研究了阳极电流密度及阴/阳电流密度比、正/负占空比、频率及氧化时间对膜层特性的影响，确定出最佳工艺参数为：阳极电流密度ja=10A/dm2，阴/阳极电流密度比jc/ja=0.7，正占空比(+)=15%，负占空比(-)=10%，频率f=300Hz，氧化时间t=45min。通过扫描电子显微镜（SEM）、X射线衍射仪（XRD）对最优工艺参数下制备出的陶瓷层微观形貌及相结构进行表征。结果表明，微弧氧化膜层表面呈“火山口”状凸起，孔径1～3μm；膜层与基体之间呈微区范围内的锯齿状冶金结合，厚度可达31.1μm，连续致密，显微硬度高达1080；膜层主要由γ-Al2O3组成，而-Al2O3含量较低。对在不同氧化时间下制取的陶瓷层的性能进行表征，结果表明，陶瓷层的耐蚀性和耐磨性较基体均有较大幅度的提高，在优化出的工艺参数下制备出的陶瓷层经历240h盐雾实验后未出现腐蚀，其腐蚀电位（-0.589V）较基体（-0.772V）有183mV的提高，且其腐蚀电流密度（1.281×10-9A/cm2）也较基体（8.053×10-5A/cm2）降低了4个数量级。同时，陶瓷层的耐磨性提高了3个数量级，而力学性能损失幅度并不大。为探究Cu、Mn、Mg、Si、Zn等主要合金元素对微弧氧化陶瓷层的厚度、显微硬度、微观形貌、相结构及组成的影响，本文熔炼成一系列不同Cu、Mn、Mg、Si、Zn含量的铝合金在相同工艺参数下对其进行微弧氧化处理，研究结果表明：不同基体材料所制备出的陶瓷层表面呈凹凸不平，有大量孔洞及片状堆积，均由γ-Al2O3及少量-Al2O3组成。Cu元素及Si元素可促进-Al2O3的形成，但当其含量过高时体现为抑制作用；Mg元素在ω(Mg）<0.8%时，促进等离子体电解氧化的进行，当0.8%<ω(Mg）<2.5%时又体现为极大的阻碍作用，随着Mg含量进一步提高，又开始促进等离子体电解氧化的进行，但效果不明显；Zn元素整体表现为对高温氧化铝相的形成有强烈阻碍作用，其含量越高，阻碍作用越明显。更多还原

【Abstract】 Aluminum and its alloys are widely applied due to its advantages such as lightweight, highspecific strength, good toughness and formability, but some shortcomings such as low hardnessand poor corrosion resistance and abrasive resistance limit its application. Special and excellentperformances can be obtained after ceramic technology on surface of aluminum and its alloys.Technology of micro-arc oxidation (MAO) is an emerging surface treatment process onaluminum, magnesium, titanium and their alloys. In-situ ceramic coatings formed by micro-arcdischarge have high hardness, good corrosion resistance, good abrasive resistance and excellentadhesion to substrate. Therefore, the technology is widely used in the field of machinery,electron, spinning and aerospace.Electrolyte parameters, electrical parameters, alloying elements in matrix material are keyfactors which influence the performance of ceramic coatings on aluminum alloys. Orthogonalexperiment was used in this paper to optimize the best electrolyte parameters to preparemicro-arc ceramic coatings on aluminum alloy7075in electrolytic systems of sodiumaluminate, sodium silicate, sodium borate and sodium phosphate. Based on the best electrolyteparameters above, electrical parameters such as current density, duty cycle, frequency, andoxidation time were optimized by using single factor analysis under experimental index ofthickness, micro-hardness and microstructure of ceramic coatings. Corrosion resistance,abrasive resistance and mechanical properties were characterized of ceramic coatings preparedin different oxidation time, influences of alloying elements in substrate during the process ofmicro-arc oxidation were analyzed. Conclusions obtained during the experiment were listedbelow:By orthogonal experiment, the best electrolyte parameters to prepare micro-arc ceramiccoatings on aluminum alloy7075in electrolytic systems of sodium aluminate, sodium silicate,sodium borate and sodium phosphate were:Sodium aluminate: sodium aluminate9g/L, sodium hydroxide1g/L, trethanolamine6ml/LSodium silicate: sodium silicate8g/L, sodium hydroxide1g/L, trethanolamine6ml/LSodium borate: sodium borate15g/L, sodium hydroxide1g/L, trethanolamine6ml/LSodium phosphate: sodium phosphate12g/L, odium hydroxide1g/L, trethanolamine6ml/LThickness, micro-hardness, surface and cross-section morphology of ceramic coatingsprepared in the electrolyte above were tested and analyzed, sodium aluminate system waschosen for its best ceramic coatings quality. By using the best electrolyte parameters and singlefactor analysis, effects of anodic current density and cathode/anodic current density ratio,posive/negative duty cycle, frequency and oxidation time on coating properties were discussedin detail. The optimum electrical parameters were proposed as follows: anodic current densityof10A/dm2, cathode/anodic current density ratio of0.7, positive duty cycle of15%, negative duty cycle of10%, frequency of300Hz, oxidation time of45min.The microstructure and morphology of ceramic coatings were observed by using scanningelectron microscope (SEM) and X-ray diffraction (XRD). The results showed that,embossments like “volcanic vent” were presented on the surface of MAO coatings prepared inthe optimal technological parameters with diameters of micro-holes between1and3μm. Inaddition, metallurgical bonding mode like zigzag was observed between coating and substrate,coatings were continuous and compact with thickness of31.1μm and micro-hardness ofHV1080. Coatings were mainly composed of γ-Al2O3and little-Al2O3.Properties of ceramic coatings prepared in different oxidation time were characterized,results showed that, corrosion resistance and abrasive resistance were improved significantly.Corrosion hadn’t occurred on ceramic coatings prepared under the best technical parametersafter salt spray test of240hours, its corrosion potential(-0.589V) was higher thansubstrate(-0.772V), and its corrosion current density (1.281×10-9A/cm2) had decreased4ordersthan substrate(1.281×10-9A/cm2). At the same time, the abrasive resistance had improved by3orders while the mechanical properties just lost little.In order to research the influences of alloying elements such as Cu, Mn, Mg, Si and Zn onthickness, micro-hardness, microstructure and phase composition, a series of aluminum alloyswhich contained different content of alloying elements were smelted, and micro-arc oxidationwas carried out under the same technical parameters, results showed that, the phase of ceramiccoatings prepared on different substrates were composed of γ-Al2O3and little-Al2O3. elementCu and Si can promote the formation of-Al2O3, while suppression was reflected when theircontent was too high. Auxo-action was presented when mass percent of element Mg below0.8,while inhibitional effect was presented when mass percent of element Mg between0.8and2.5,besides, element Mg promote the process of micro-arc oxidation with unconspicuous effect.Element Zn had strong inhibition effect on the formation of high temperature phase of alumina,and the effect became stronger with the content of Zn increasing.更多还原