Characterization of Low-Pressure Cold-Sprayed Aluminum Coatings

Aluminum alloys are widely used as materials for engineering components of automobiles and airplanes because of their light weight and high corrosion resistance. However, cracks may develop sometimes in aluminum components, which have to be repaired by welding. It is difficult to weld aluminum components due to its high specific thermal conductivity and high coefficient of thermal expansion. The low-pressure cold-spray technique can be used instead of welding for repairing cracks. However, the effects of surface conditions on particle deposition and the mechanical properties of cold-sprayed coatings have not been investigated thus far. In this study, the effect of surface conditions focusing on active newly formed surface on aluminum particle deposition is studied and the mechanical properties of low-pressure cold-sprayed aluminum coatings are investigated by four-point bending tests. It is found that for efficient particle deposition it was necessary to obtain active newly formed surface of the substrate and particle surfaces by several impingements because the existence of inactive native oxide films has an adverse effect on the deposition. Furthermore, the strength of a cold-sprayed specimen is found to be higher than that of a cold-rolled specimen under compressive loading.     

Preparation and Microstructure Characterization of Mullite Coatings Made of Mullitized Natural Andalusite Powders

Natural andalusite powders were heated at high temperature in air allowing mullitization. The mullitized powders were spray-dried and then air plasma sprayed to form mullite coatings. Microstructure and phase composition of the plasma-sprayed mullite coatings were investigated by means of scanning electron microscopy and x-ray diffraction. The effect of spraying power on the microstructure and phase composition of the mullite coatings was investigated. It has been found that spraying power has significant effect on the content of amorphous phase in the mullite coatings. At the same time, good adhesion is reached between the mullite coating and the bound coating (NiCrAlY) and between the bound coating and the substrate. The mullite coating deposited at a spraying power of 22.5 kW is free of cracks. The processes reported here are applicable to preparing mullite coatings used in high-temperature environment.     

Protective CVD Mullite Coatings on Single-Crystal Silicon Substrates

Silicon has long been the primary material of choice for microelectromechanical systems (MEMS) and integrated circuit (IC) applications. However, it is prone to degradation under severe conditions such as high humidity, high temperature, and corrosive environments. To overcome such extreme conditions and help silicon perform with stability and extended lifetimes, a protection layer is proposed. Mullite (3Al₂O₃·2SiO₂) is a known environmental barrier coating (EBC) material and has been shown to be effective on other Si-based ceramic materials. In this work, dense, high-purity crystalline mullite coatings were deposited onto single-crystal silicon substrates via chemical vapor deposition (CVD). The microstructure, orientation preference, and adhesion of these coatings were investigated. Substrate integrity in relation to the substrate/coating interface by chemical etching and coating stability in a simulated severe environment under corrosive alkali salts were investigated.     

Fabrication and Characterization of Squeezed Cast Aluminum Matrix Composites Containing Boride Reinforcements

Aluminum alloys containing 2 and 4 wt.% copper reinforced with aluminum dodecaborides were successfully fabricated by squeeze casting employing pressures up to 62 MPa. The distribution of reinforcements throughout the composites was quantified, whereas the effect of pressure on the composites density and hardness was determined. In addition, the reinforcement chemical stability was examined using high-temperature x-ray diffraction which permitted to confirm the formation of AlB₂ phase a result of AlB₁₂ decomposition. The pressure effect on the squeezed composites was investigated by optical microscopy, Vickers microhardness testing, superficial Rockwell hardness testing, and differential thermal analysis. At the highest applied pressures, the castings density increased when the shrinkage porosity was practically eliminated. The composite superficial hardness improved by increasing the applied squeeze. The indirect squeeze cast technique caused Al₂Cu phase segregation to upper regions of the specimens, while conversely, the AlB₁₂ reinforcements segregated preferentially at lower regions of the casting.     

耐碱蚀铝铸铁的研究

针对国内氨碱生产系统工艺管道所使用的灰铸铁耐蚀性较差的问题进行了耐碱蚀铝铸铁的研究。对相同C、Si含量的铝铸铁和灰铸铁的耐碱蚀性进行了对比实验,结果表明铝的加入对铸铁的耐碱蚀性能有明显影响。     

耐碱蚀铝铸铁的研究

针对国内氨碱生产系统工艺管道所使用的灰铸铁耐蚀性较差的问题进行了耐碱蚀铝铸铁的研究。对相同C、Si含量的铝铸铁和灰铸铁的耐碱蚀性进行了对比实验，结果表明铝的加入对铸铁的耐碱蚀性能有明显影响。     

烧成窑托轮轴瓦的铸造

φ4.5 m×110 m烧成窑是氧化铝生产中使用的大型设备,其托轮的轴瓦是采用给轴承淋油的方式润滑.托轮与轴瓦之间存在临界滑动摩擦.该轴瓦承受载荷大,磨损消耗大,材质ZQAl9-4轴瓦两端带法兰,工艺设计时浇冒口大小及位置受到限制,补缩效果受影响,有缩松及小裂纹.针对缺陷,提出防止对策.     

浅谈铝电解所用铸造铝母线的质量控制

在铝电解生产中 ,铸造铝母线的使用量大 ,制作安装质量要求高 ,且直接关系到电解铝厂的安全生产和节能降耗。故应严格按照铝母线的质量检验标准和规程的要求 ,做好质量控制工作。     

铸铁用浅色涂料的研究

通过试验,优选出两种铝钒土浅色涂料,并在实际应用中获得了良好效果。     

铸造铝合金微弧氧化工艺及其优化

采用对比试验的方法,调整电解液组分及浓度,研究降低含有Si、Cu元素的铸铝合金、微弧氧化电流密度的电解液.结果表明:在硅酸盐体系中添加适量的柠檬酸钠、草酸铵等,可减小Si、Cu元素对微弧氧化的不利影响,降低微弧氧化电流密度,降低能源消耗.     

Chromateless Conversion Protective Coatings on 1441 Aluminum Alloy

Protection of Metals and Physical Chemistry of Surfaces - The presence of copper-containing intermetallide phases significantly decreases the corrosion resistance of 1441 aluminum alloy. Because...     

高铬铸铁表面制备陶瓷涂层的研究

以Ti-B4C-蔗糖-Al和Ni-Al自粘结复合粉为喷涂体系,通过白蔓延反应火焰喷涂技术,采用梯度过渡涂层设计,在高铬铸铁泵叶表面制备了梯度过渡陶瓷涂层.主要研究了喷涂工艺、涂层性能以及喷涂前后基体组织及性能变化等问题.结果表明:利用自蔓延反应火喷涂技术在高铬铸铁表面制备梯度过渡陶瓷涂层是可行的:引入梯度过渡涂层设计后尽管使涂层的显微硬度有所下降,涂层孔隙率有一定增大,但可以明显改善陶瓷涂层与基体的结合,提高结合强度,同时不会造成基体材料和性能发生明显变化.     

铸造铝合金中氧化夹杂物的研究进展

就铸造铝合金中氧化夹杂物的来源和形成过程、对铝液吸氢、铝铸件中孔洞形成和铸件力学性能的影响进行了分析,并对国内外铝合金铸件中氧化夹杂的研究进展进行了综述.在熔铸过程中形成的氧化夹杂物,是铝液中夹杂物的主体,对铝液吸氢和铝合金铸件中孔洞的形成有着不可忽视的影响.铝合金铸件的力学性能与铝液中的氧化夹杂密切相关,夹杂物可作为显微裂纹的发源地,严重削弱铝合金铸件的力学性能.     

Chromium-Free Conversion Protective Coatings on 1424 Aluminum Alloy

Protection of Metals and Physical Chemistry of Surfaces - Abstract—It is known that lithium-containing aluminum alloys possess low pitting corrosion resistance. It has been previously shown...     

铸造铝合金轮毂T6热处理工艺的优化研究

研究了固溶时间、淬火停留时间及涂装烘烤工艺对A356合金铸造轮毂性能的影响规律并优化了T6热处理工艺，将淬火停留时间缩短到2h。研究表明：未涂装时优化工艺使合金抗拉强度达到240MPa，屈服强度达到181MPa。伸长率达到8％；涂装后抗拉强度达到262MPa，屈服强度达到179MPa，伸长率达到9％，接近并达到目前国内T6工艺的强度性能，超过了国内轮毂行业的强度性能标准，具有一定的生产实际意义。     

铸造铝合金轮毂T6热处理工艺的优化研究

研究了固溶时间、淬火停留时间及涂装烘烤工艺对A356合金铸造轮毂性能的影响规律并优化了T6 热处理工艺,将淬火停留时间缩短到2 h。研究表明:未涂装时优化工艺使合金抗拉强度达到240 MPa,屈服强度达到181 MPa,伸长率达到8％;涂装后抗拉强度达到262 MPa,屈服强度达到179 MPa,伸长率达到9％,接近并达到目前国内T6工艺的强度性能,超过了国内轮毂行业的强度性能标准,具有一定的生产实际意义。     

稀土对机械镀锌铝镀层中微量铝的影响

通过铬天青S分光光度法测定了机械镀锌铝镀层中铝的含量、用扫描电镜及X射线荧光光谱仪测试镀层断面形貌和表面铝分布状况。结果表明,在机械镀锌铝镀层过程中加入稀土能增加镀层中的铝含量,并使铝的分布均匀化。     

Plasma Electrolytic Oxidation of Arc-Sprayed Aluminum Coatings

Different posttreatment methods, such as heat treatment, mechanical processing, sealing, etc., are known to be capable to improve microstructure and exploitation properties of thermal spray coatings. In this work, a plasma electrolytic oxidation of aluminum coatings obtained by arc spraying on aluminum and carbon steel substrates is carried out. Microstructure and properties of oxidized layers formed on sprayed coating as well as on bulk material are investigated. Oxidation is performed in electrolyte containing KOH and liquid glass under different process parameters. It is shown that thick uniform oxidized layers can be formed on arc-sprayed aluminum coatings as well as on solid material. Distribution of alloying elements and phase composition of obtained layers are investigated. A significant improvement of wear resistance of treated layers in two types of abrasive wear conditions is observed. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.