Study of shrinkage porosity in spheroidal graphite cast iron

This study aims at identifying the relationship between the shrinkage cavities and the solidification structure in spheroidal graphite cast iron. Cast samples specially designed to contain shrinkage cavities were used. The solidification macrostructure was revealed using the Direct Austempering After Solidification method, while the solidification microstructure was revealed by using colour etching. At the midsection of the pieces, the shrinkage cavities and the solidification structure were observed jointly. The study showed that the classification of shrinkage porosity found in literature does not correspond to the ductile iron solidification model recognized by most of the scientific community. Early solidification models, and therefore shrinkage formation mechanisms, were proposed in instances when there was not a thorough knowledge of the morphology of the solid phases during solidification. Nowadays, defects formation mechanisms can be described with higher accuracy. Therefore, an updated classification of shrinkage porosity for spheroidal graphite iron is proposed.     

压力铸渗法制备金属基复合材料

复合材料其有高强度、硬度以及良好的耐磨性等优良的性能。在矿山机械、航灭、交通、结构材料等领域具有广阔的应用前景。材料研究工作者对金属基复合材料的研究日益深入和广泛，因此，制备金属基复合材料的工艺技术也得到了迅速的发展。压力铸渗法是一种非常有效的方法，在这种工艺技术中．液态金属在压力作用下渗入到增强体颗粒或纤维制成的预制型中，冷却后即可得到分布均匀的复合材料。利用这种工艺制备的复合材料不仅能满足使用要求，而且可以得到净成型工件。在本文中主要针对陶瓷颗粒预制型的压力铸渗的研究进行阐述。     

Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash(ISSA) and dredged contaminated marine sediments(CMSs) is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity.The present study investigates the use of high content(20% of sediment by mass) of ISSA in combination with cement/lime for solidification/stabilization(S/S) treatment of CMSs to provide a way to reuse the wastes as construction materials.The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content(～80%).The S/S treatment improved the engineering properties of the sediment,but reduced the workability,especially for the lime-treated samples.Lime can be used to replace ordinary Portland cement(OPC) for better heavy metal immobilization and carbon emission reduction.The hardened sediment samples prepared with 10% of lime and 20% of ISSA could attain a strength of 1.6 MPa after 28 d of curing.In addition,leaching tests confirmed that there was no environmental risk induced by these stabilized materials.The formation of hydrated cementitious compounds including calcium silicate hydrate(C-S-H)/calcium aluminate silicate hydrate(C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.     

含硼废液水泥固化技术综述

压水堆核电厂含硼废液的处理主要采用水泥固化方法,这些方法大致可分为五种,即常规水泥固化工艺、改进型水泥固化工艺、高减容水泥固化工艺、制粉造粒灌浆固化工艺和高效率固化工艺。通过对各固化工艺特点的分析,提出我国应在制粉造粒灌浆固化工艺方面加强研究。     

脉冲电流在金属凝固过程中的作用及研究进展

综述了国内外关于脉冲电流处理对金属凝固组织和对合金性能影响的研究概况,根据电磁学和金属凝固原理,分析了电脉冲细化金属晶粒和改善合金性能的原因,揭示了电脉冲影响金属凝固的主要机制,并对其影响规律进行了理论推测。     

铝合金发动机缸盖铸造工艺的计算机模拟分析

在对铝合金发动机缸盖进行工艺分析的基础上,制定了3组浇注方案,分别为缝隙式顶冒口补缩浇注系统、顶冒口直接浇注系统、半开放式半包围型横浇道浇注系统.通过使用铸造数值模拟软件对金属液的充型和凝固过程进行数值模拟,认为缝隙式顶冒口补缩浇注系统为最优方案.确定了缸盖的优化工艺参数:模具预热温度为400℃,浇注温度为720℃.在该组优化的工艺参数下,通过对金属液的充型和凝固过程的动态观察,预测了充型时间、凝固时间和可能存在的缩松、缩孔及气孔缺陷的分布与体积分数.     

汽车空调器动盘挤压铸造技术研究

用直接挤压铸造和间接挤压铸造两种工艺生产汽车空调器动盘重要部件。针对该铸件的结构特点,设计的两种不同结构的模具均能生产出合格的动盘零件,研究了两种模具的结构特点和工作原理。经测试,直接挤压铸造的动盘的硬度比间接挤压铸造的高5%～10%,但铸件尺寸控制较麻烦,产品尺寸精度难以保证。     

真空浇注条件下镁合金石膏型压力凝固的研究

研究真空浇注条件下镁合金石膏型压力凝固过程中浇注温度、真空度对镁合金流动性的影响及凝固压力、操作时间与镁合金拉伸性能的关系.结果表明,高真空度和高浇注温度条件下,可使镁合金液在石膏型中获得很好的充型.铸件凝固过程中,凝固压力越高,操作时间愈短,得到的铸件组织越致密,拉伸性能愈高.     

水玻璃的固化机理及其提高耐水性途径分析

伴随环保要求的提升和人们环境意识的提高,水玻璃作为一种环境友好型粘结剂受到广大研究者以及消费者的垂青。但水玻璃因其自身的结构而导致的固化后耐水性差的问题尚未得到彻底的解决,不同的固化途径而产生的固化机理亦是琳琅满目,从而使水玻璃在其应用原理以及解决其相应的缺陷上受到阻碍。笔者对近几年来所研究的水玻璃固化机理以及提高其耐水性途径进行了详细的分析,以促进和拓宽水玻璃的改性研究及应用领域。     

一种基于Ag-Sn等温凝固的圆片键合技术

研究了用Ag-Sn作为键合中间层的圆片健合。相对于成熟的Au-Sn键合系统(典型键合温度是280℃),该系统可以提供更低成本、更高键合后分离(De-Bonding)温度的圆片级键合方案。使用直径为100mm硅片,盖板硅片上溅射多层金属Ti/Ni/Sn/Au,利用Lift-off工艺来形成图形。基板硅片上溅射Ti/Ni/Au/Ag。硅片制备好后,将盖板和基板叠放在一起送入键合机进行键合。键合过程在N2气氛中进行,键合过程中不需要使用助焊剂。研究了不同键合参数,如键合压力、温度等对键合结果的影响。剪切强度测试表明样品的剪切强度平均在55.17MPa。TMA测试表明键合后分离温度可以控制在500℃左右。He泄漏测试证明封接的气密性极好。