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.     

大气等离子喷涂莫来石粉末及制备涂层的结构表征

喷雾造粒制备莫来石粉末,采用大气等离子设备对造粒粉末进行等离子球化和涂层制备.利用激光粒度分布仪对粉末粒度分布进行测试;扫描电镜和X射线衍射仪分别表征了粉末和涂层的相组成和微观形貌.结果表明:喷雾造粒和等离子球化后的莫来石粉末粒径为正态分布;造粒的莫来石粉末主要由晶态莫来石和SiO2相组成;等离子球化后,粉末中出现玻璃态非晶相;等离子球化过程中,较小粒径粉末表面基本上完全熔融,较大粒径粉末的表面为部分熔融;同时,制备的莫来石涂层具有良好的微观形貌和较高的显微硬度;涂层经热处理后,非晶相转变为晶态莫来石,并且有部分石英相析出.     

2004年起中国将启用新的金属废料分类目录及报关方法

在交流条件硅酸钠溶液中利用微等离子体氧化技术合成了陶瓷涂层。通过XRD，EPMA分析了所得陶瓷涂层在不同层面上的相组成、微观结构及元素分布。由陶瓷涂层截面的背散射图看出陶瓷涂层较致密、与基体结合强度高。XRD分析结果显示，陶瓷涂层的最外层由莫来石及γ-Al2O3相组成，随着向陶瓷涂层内部的移动，莫来石的含量逐渐减少，α-Al2O3，γ-A12O3相的含量逐渐提高，而且陶瓷涂层的颜色由白色逐渐变为黑色。硅元素在陶瓷涂层的外侧及陶瓷涂层与基体的交界处陶瓷涂层一侧含量较多，在陶瓷涂层中间含量少。而陶瓷涂层的硬度变化也出现了中间高，两侧低的分布情况。     

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.     

铸造铝基复合材料的凝固过程

铝基复合材料中,增强体的加入使金属凝固过程的形核、晶体生长、溶质分配和流体流动行为发生改变,特别是不同压力和冷却条件下的非平衡凝固状态下。从而对基体组织的形态、二相析出、溶质偏聚、界面反应性、凝固缺陷等产生重要影响,最终影响复合材料的性能。基于此,综述凝固过程中铝基复合材料组织与性能的作用规律。     

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。     

铸铁及其表面碳化钨涂层的电化学行为

考察了甲醇汽油发动机缸套材料铸铁及其表面碳化钨涂层在甲酸水溶液中的腐蚀性能,并研究了其电化学腐蚀行为;采用电化学腐蚀中的极化曲线和电化学阻抗来表征其电化学腐蚀性能。结果表明：碳化钨涂层可有效地改善甲醇汽油发动机缸套材料铸铁的耐腐蚀性能;与铸铁相比,碳化钨涂层的自腐蚀电位高、自腐蚀电流小;同时碳化钨涂层使铸铁表面电荷的传输电阻变大,抑制了铸铁在甲酸溶液中的自放电功能,阻碍了电化学腐蚀的进行,从而有效地保护发动机缸套材料铸铁。     

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.     

铝表面超疏水复合涂层的制备及其表面性能

目的 通过在纯铝表面构筑超疏水涂层,优化金属铝表面,并强化其应用性能。方法 采用阳极氧化法在铝表面构筑具有纳米孔洞的Al2O3薄膜,再利用全氟癸基三乙氧基硅烷修饰表面,得到超疏水复合涂层,并研究氧化电位和表面修饰时间对纳米结构的构筑及疏水性能的影响,研究超疏水复合涂层表面润湿性、防污、自清洁和抗结冰性能。结果 控制阳极氧化条件,在氧化电位为16～18V、氧化时间为1h时,得到1～2μm的“花瓣”聚集叠加成的多级粗糙结构。通过6 h的表面修饰,得到了接触角为163.6°的超疏水性复合膜层。进一步对该超疏水膜层的性能进行分析发现,经超疏水膜层修饰后铝具有优异的防污性能;相较于纯铝,经超疏水膜层修饰后铝片的电化学阻抗模值高达105?·cm2,而电流密度仅为1.81×10-9 A/cm2;在高温和低温环境下,超疏水膜层均能保持超疏水性能;经砂纸来回打磨200 cm后,膜层的接触角仍大于150°。结论 经阳极氧化纯铝得到具有多级粗糙结构的阳极氧化膜,并通过表面修饰可制备接触角高达163.6°的超疏水性复合膜层。该超疏水复合涂层具有优异的耐腐蚀性、自清洁性、耐污染性,以及良好的耐蚀性、机械稳定性和...     

铝合金表面硅酸盐转化膜研究

采用硅酸盐方法对铝合金（3A21）进行表面处理,以盐雾测试作为评价其防腐效果的方法,优化了转化液中各个组分的浓度配比和工艺参数;同时讨论了添加剂对其防腐效果的影响。实验结果表明,硅酸钠的浓度对转化反应有很大的影响,添加剂对提高其防腐能力有一定的效果。     

Sol-Gel法制备莫来石陶瓷涂层的结构及性能

采用溶胶-凝胶法在不锈钢基体上制备了莫来石涂层。研究了助熔剂和灼烧温度对涂层表观形貌的影响。利用XRD、TG-DTA和SEM分析涂层相组成和微观结构,并对涂层的高温抗氧化性和显微硬度进行了评价和测定。结果表明:当B2O3与莫来石溶胶质量比为0.5时,在850℃下灼烧所得涂层结构致密,与基体结合力强,显微硬度高达12 GPa,在800℃下样品具有优异的抗氧化性和良好的高温稳定性。