铝合金表面微弧氧化技术的研究进展

论文介绍了铝合金表面微弧氧化技术的研究进展,重点总结了近年来研究者在陶瓷膜形成机理、陶瓷膜性能及陶瓷膜结构等方面的研究成果,并预测了微弧氧化技术发展趋势,为从事这方面的研究人员提供一定的理论指导。     

铝及其合金的阳极氧化

<正> 铝和铝合金的阳极氧化是一种利用电解液中的阳极反应,而生成铝氧化膜的电化学过程。它能很有效地提高纯铝及其合金的表面硬度、耐磨性、抗蚀性、绝缘性和染色性;在精密仪器仪表、日用品、工艺品、国防用品和机械另件等制造工业中,得到了广泛的应用。阳极氧化方法包括硫酸法、草酸法、铬酸法和草酸钛钾法等。其中硫酸法因具有成本最低、耗电量小、操作方便,并适用于各种纯铝和铝合金的阳极氧化等多种优点,所以应用最广。本文着重研讨硫酸法的阳极氧化工艺及其有关原理。     

铝及其合金电化学复合处理技术及研究进展

叙述了铝及其合金表面一次和二次电化学复合处理技术，发展概况以及它们的特点和适用范围。重点介绍一次电化学复合处理技术，即复合阳极氧化方法。该方法工艺简单，成本低，适用范围广，溶液稳定，膜层性能优良。但是，还应加强对粉体细度及电化学复合机理方面的研究。     

Oxidation of Composite Materials Based on Aluminum Nitride

A method for studying the heat resistance of composite aluminum nitride-based ceramic materials in air at 1073 – 1273 K is developed that allows the change in mass to be measured with an accuracy of 0.15 – 0.17 mg. The interaction between AlN-based composite materials and a phosphate binder (H₃PO₄) is studied and compared with hot-pressed specimens. A mechanism for the effect of the binder on the kinetics of oxidation is proposed. The relatively low activation energies (152 and 205 kJ/mole) suggest that the oxidation process is mainly determined by the diffusion of aluminum ions through the -Al₂O₃ film.     

铝合金无铬化学氧化工艺的研究进展

研究和开发实用性强、环境友好型铝合金化学氧化工艺是未来发展的方向。综述了国内外几种主要铝合金无铬化学氧化工艺的特点及发展现状,其中包括锆酸盐氧化、钛酸盐氧化、钼酸盐氧化、锂盐氧化、高锰酸盐氧化、稀土金属盐氧化及有机类氧化等工艺。并对铝合金无铬化学氧化工艺的研究方向进行了展望。     

铝及铝合金高耐蚀性化学氧化新工艺

介绍CZ99-03（11）铝及铝合金高耐蚀性化学氧化新工艺，并检测氧化膜性能，显示湖绿色氧化膜优良的耐酸碱性能以及与涂料的配套性，对提高铝制品的防护及改善涂层质量。     

铝硅合金热氧化膜层耐电化学腐蚀性能

采用SEM、全浸渍、色度测试等测试方法研究铝合金热氧化法制得氧化膜层表面形貌和耐蚀性能。结果显示:氧化后,耐蚀性明显增强,并且氧化温度越高,得到的氧化层耐蚀性越好;相同温度下,随着氧化时间的延长,耐蚀性越好,氧化8 h后继续氧化,耐蚀性趋于稳定;在纯氧中氧化的耐蚀性优于在空气中氧化;耐蚀性好的膜层表面偏灰,略成黄色。     

铝在钼酸盐复合电解液中的阳极火花氧化

采用阳极火花氧化处理技术，在含有钼酸盐等金属盐的碱性电解液中，通过阳极氧化在铝表面形成了复合转化膜。对电解液中的各组分在成膜过程中的作用及电解工艺参数对成膜过程和膜层性能的影响进行了研究探讨。通过与铬酸盐化学氧化法、常规阳极氧化法相比较，结果表明，铝表面阳极火花氧化方法形成的膜层比其它膜层有着更好的功能特性。     

铝合金微弧氧化陶瓷膜的形成过程及其特性

分析了微弧氧化陶瓷膜形成过程，描述了样品表面微区弧光放电现象，并采用Ｘ射线衍射法（ＸＲＤ）和扫描电镜（ＳＥＭ）研究了ＬＹ１２铝合金微弧氧化陶瓷膜的相组成及形貌特征。结果表明，铝合金微弧氧化陶瓷膜主要α－Ａｌ２Ｏ３、γ－Ａｌ２Ｏ３组成，陶瓷氧化膜具有表面疏松层、致密层两层结构。微弧氧化技术是一种非常有前途的新技术。     

Influence of Magnesium-Aluminum Spinel on the Directed Oxidation of Molten Aluminum Alloys

The directed oxidation of some molten aluminum alloys was studied. Alloys containing Si, Zn, and Mg are readily converted into Al₂O₃/Al composites with the characteristic directed metal oxidation process (DIMOX) metal-channel structure. No reaction took place when alloys without Mg were used. However, when Mg-free melts containing Si and Zn were in contact with bulk spinel (MgAl₂O₄), the typical reaction product grew from the metal pool, although without formation of the spinel starter layer which was thought to be a prerequisite for DIMOX growth. Furthermore, the growth front was more planar than when Mg-containing alloys were used.     

Oxidation of Powdered Alloys of Aluminum and Cerium during Heating in Air

The effect of cerium on the oxidation of powdered alloys of aluminum and cerium during heating in air at temperatures up to 1773 K was studied using derivatography, xray phase analysis, and thermal desorption of argon. It is established that the rate and completeness of the oxidation of aluminum increase if it is alloyed with cerium. The effect of cerium is due to its polyvalence, high reactivity, and surface activity toward aluminum. Structural and phase nonuniformities that arise during the growth of oxide phases on the surface of oxidized particles of the alloys enhance the interaction of these particles with air oxygen. It is shown that the assumptions that the surfaces of the alloys have a micrononuniform structure and are enriched with CeAl₂ and CeAl₄ groups are valid.     

铝合金阳极氧化技术研究进展

铝合金表面处理技术能够很好地清洁材料表面,结合阳极氧化技术能够提高铝合金基体表面的硬度、耐蚀性和耐磨性。本文概述了多种阳极氧化的工艺,为研究新技术工艺、开拓新应用领域提供了有力支持。     

Early Stages of Diamond-Film Formation on Cobalt-Cemented Tungsten Carbide

The surface composition of cemented tungsten carbide (WC-5.8 wt% Co) was studied by X-ray photoelectron spectroscopy (XPS), during the early stages of diamond-film deposition, by hot-filament chemical vapor deposition (HFCVD). The nucleated diamond films were analyzed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and automatic image analysis (AIA). The evolution of the surface composition of cemented tungsten carbide during the early stages of diamond-film deposition was strongly dependent on the substrate temperature. At relatively low temperature (750°C), cobalt-rich particles started to segregate at the substrate surface after a few minutes of diamond deposition. The conspicuous segregation of the binder partly inhibited the formation of stable diamond nuclei, through intense carbon dissolution or carbon segregation at the binder surface, but did not affect nucleic growth. At higher temperatures (940°C), no cobalt-rich particles formed at the substrate surface, even after 2 h of deposition. However, XPS results demonstrated the presence of cobalt in a surface layer, although in a lower amount than at 750°C. Nevertheless, the nucleation density of diamond at 940°C was much lower than at 750°C. Gaps between WC grains formed within 10 mins. Therefore, intergranular cobalt was removed at 940°C, a finding attributed to the etching performed by monohydrogen, rather than to binder evaporation. The time evolution of the substrate area fraction covered by diamond islands, S ( t ), was well described by Avrami kinetics for two-dimensional phase transformations, suggesting that diamond formation took place via a heterogeneous nucleation process. The S ( t ) functions exhibited a similar trend at 750° and 940°C, because the higher growth rate of diamond crystallites at higher temperature counteracted the slower nucleation rate at the higher temperature.     

Kinetics of Metal-Ceramic Composite Formation by Reactive Penetration of Silicates with Molten Aluminum

Wetting and reactions between molten Al and silicate substrates (particularly mullite) are studied to determine both how substrate tensity and p (O₂) influence wetting behavior, reaction rates, composition, and reaction product microstructure and what key steps control penetration kinetics. Guidelines are provided for using reactive penetration or infiltration when fabricating metal/ceramic composites. For dense substrates, a reactive penetration process occurs. For a certain range, the chemical reaction between Al and the ceramic is a limiting kinetic step resulting in fast reaction rates. Maximum dense mullite substrate reaction rates are between 1000° and 1200°C independent of p (O₂), unlike fused silica, which has faster penetration rates at higher temperatures. For mullite, reaction layer microstructure evolution halts reaction at higher temperatures. For porous substrates, reactive infiltration alone occurs. Either a critical temperature or p (O₂) must be reached before infiltration starts.     

Wetting of Aluminum Nitride by Nickel Alloys

The effect of the addition of alloying elements to Nion Ni wetting of AIN was investigated. Pure Ni is nonwetting, but adding Hf, Zr, or Ti caused Ni to wet, whereas V, Nb, Ta, Cr, Mo, and W did not change the wetting angle. In wetting systems, the alloying elements form nitrides and the change in the wetting angle is related to the change in the Gibbs free energy of formation of the nitrides formed in the contact layer.     

Special Features of Oxide Layer Formation on Magnesium Alloys during Plasma Electrolytic Oxidation

The process of the oxidation of magnesium alloys in a silicate electrolyte during plasma electrolytic oxidation is investigated. An anomalous form of the chronogram of the formation voltage of the oxide layer in the electrolytes with the highest silicate concentration (approximately 0.15 M Na₂SiO₃ · 5H₂O) is detected. X-ray diffraction analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy analysis, and thickness gauges are used to characterize the surface microstructure, phase composition, and thickness, respectively. Mechanisms for the initial period of PEO and the “insular” growth were described. During the “insular” growth, islands consisting of vitrified components of the electrolyte are growing on the original smooth surface.     

Effect of Silica Surface Dopants on the Formation of Alumina/Aluminum Composites by the Directed Metal Oxidation of an Aluminum Alloy

This study focused on clarifying the effect of SiO₂ surface dopants on the formation of Al₂O₃/aluminum composites, especially on oxidation phenomena during the incubation period. The present results showed that a surface dopant decreased the incubation period of an Al-Mg-Si alloy, as well as that of an Al-Mg alloy, and that addition of an external surface dopant decreased the incubation period more effectively than did an internal alloying of silicon. A two-step oxidation process was also conducted. In the first step of the process, an aluminum alloy was oxidized without a surface dopant and cooled to room temperature during the incubation stage. In the second step, the same specimen was surface-doped with SiO₂ powder and reoxidized. The incubation time for the specimen subjected to the two-step oxidation process was the same as that for the single-step specimen oxidized with a surface dopant. The substantial decrease in the incubation period, especially for the Al-Mg alloy, is ascribed to interaction between the SiO₂ surface dopant and the MgO layer. This interaction made the MgO layer thinner and increased the number of magnesium vacancies in the MgO layer, thus providing an appropriate microstructure in the MgO layer for bulk-growth initiation.     

Structure of Aluminum Nitride/Aluminum and Aluminum Oxide/Aluminum Composites Produced by the Directed Oxidation of Aluminum

Unreinforced AlN/Al ceramic/metal composites were produced by the directed oxidation of molten Al alloys in nitrogen. The microstructures of these composites were compared with those of previously studied Al₂O₃/Al composites. In both composite systems the ceramic phase was interconnected and oriented in a columnar structure. The metallic phase showed no significant crystallographic orientation and appeared as both interconnected channels and isolated inclusions. The columns in the nitride system were found to be of micrometer size and to contain subgrains weakly defined by lattice defects, unlike the oxide system, where the columnar structure was shown to be of millimeter size and to contain well-defined micrometer-sized subgrains. Finer structures were obtained in both systems via the addition of Ni to the parent alloy.     

Strengthening and Prevention of Oxidation of Aluminum Nitride by Formation of a Silica Layer on the Surface

A silica (SiO₂) layer was deposited on the surface of an AlN ceramic in order to increase the strength and to prevent the high-temperature oxidation of the material. The layer was formed on the surface by exposing coupons to the atmosphere downstream of a bed of SiC powder in a flowing H₂–0.1% H₂O atmosphere at 1450°C. A reaction between the SiC powder and H₂O in the H₂ gas resulted in the generation of SiO₂"smoke" in the product gas stream. Part of the SiO₂ smoke was subsequently deposited on the surface of the AlN specimen to form a dense and uniform SiO₂ layer. The strength of AlN was improved by about 20% apparently because of blunting of surface defects by SiO₂. More importantly, the layer was very effective in protecting the AlN from the oxidation at elevated temperatures, through the inhibition of transport of oxidants to the sample surface.