【作者】 汪彬；

【导师】 李俐群；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2010， 硕士

【摘要】 硅颗粒增强的铝基复合材料是一种新型的复合材料,具有轻质、低膨胀、高导热、环保利于回收等优点,在航空、航天、电子封装等领域具有广阔的应用前景。这种材料一般硅颗粒所占比分较高,一旦熔化,熔池含硅量很高,凝固后往往存在大量的缩孔,组织为十分粗大的板条状硅。大大恶化了性能,失去了应用价值。本文利用激光填丝钎焊工艺,含硅量为12%的4047铝硅药芯焊丝作为填充材料,对硅颗粒增强铝基复合材料的焊接特性进行了系统的研究。首先确立了对激光钎焊工艺尤为重要的光斑类型、坡口形式两个工艺条件,从表面成型和组织形态均匀性两方面考虑,试验研究了各工艺参数对成形和组织的影响,获得了优化的工艺参数,得到了表面平滑稳定、焊缝中含有大量增强相的接头。焊缝的组成元素只有铝和硅,而铝硅之间没有直接的冶金反应,组织组成即为简单的初晶硅和共晶组织。因此焊接过程中硅的溶解扩散对其结晶行为和组织结构影响重大。本文在分析硅的溶解、扩散、结晶行为的基础上,研究了不同工艺条件下焊缝不同部位硅元素的分布、存在形式与结构特征。结果发现,焊缝中的硅主要有两种存在形态,即初晶硅和共晶硅。初晶硅为颗粒状,弥散的分布在焊缝中,共晶硅在不同的位置表现出不同的形貌,界面处为细长的针状树枝晶,在焊缝中心呈现细小的短棒状。研究后发现,这种短棒状的共晶硅是以共晶团的方式长大的。最后,为改善初晶硅的尖角和针状共晶硅的形貌,避免其尖角割裂基体并使得焊缝组织均匀,获得热膨胀系数等物理性能的各向同性。提出进行热处理,结果发现在合适的热处理工艺下(T=550°C、t=8h、随炉冷却)针状的还有短棒状的共晶硅都破碎聚集成颗粒状,初生硅的尖角也得到了钝化,焊缝组织变得均匀。更多还原

【Abstract】 Silicon particles reinforced aluminum matrix composites is a new type of composite materials. With advantages of light weight, low expansion, high thermal conductivity, environmental protection and good recyclability, it has broad application prospects in the aviation, the spaceflight, the electronic packing and other fields. However, as it has a large proportion of silicon particles in this kind of materials, which leads to a high content of silicon in the molten pool once melted, there remain a lot of shrinkages and very coarse lath-shaped Si in the material after the solidification, deteriorating the performances of the material significantly and losing the application values.In this paper, the welding characteristics of silicon particle reinforced aluminum matrix composites were investigated systematically, using the laser brazing filler wire technology, with the 4047 Al-Si (12% silicon content) flux cored wire as a filling material. First, the types of the laser spot and the groove, both of which are particularly important to the laser soldering process, were established. The effects of various processing parameters on the forming and organizations were studied through experiments, considering in the perspective of the surface forming and the uniformity of structure morphology. Optimized parameters, and the stable joints with smoothing surfaces and a high content of reinforcements in the weld, were obtained.The dissolution and diffusion of silicon during the welding has significant impact on its crystallization behavior and the structure of the material. The distributions, existing forms and structure characteristics of Si in different areas of the welds under various processing conditions were studied in this paper, based on the analysis of the dissolution, diffusion and crystallization behaviors of Si. The results show that the silicon exists mainly in two forms, namely, primary silicon and eutectic silicon, in the welds. Granular primary silicon dispersively distributes in the weld. The eutectic silicon in different locations shows different morphologies, for instance, the slender needle-like dendrites in the interfaces and the small short rods in the weld center. Studies find that the short rods of the eutectic silicon grow up in the way of eutectic clusters. Finally, the heat treatment (550°C, holding for 8h, with furnace cooling) were carried out, to improve the primary silicon’s sharp corner and the morphology of the needle eutectic silicon to prevent them from splitting the matrix and deteriorating performances. The results show that both the needle and short rod eutectic silicon have broken and assembled into granules, and the sharp-cornered primary silicon has also been passivated, making the structure of the weld uniform.更多还原