Al-30%Si合金初生硅组织形貌控制技术研究

发布时间：2018-05-06 13:31

本文选题：Al-30%Si合金 + 初生硅形态　；参考：《南京理工大学》2017年硕士论文

【摘要】：过共晶铝硅合金是一种重要的铸造合金,随着硅含量的增加,过共晶铝硅合金的耐磨性能显著提高,热膨胀系数大大降低,热稳定性提高,密度降低,耐高温性能提高。未处理的铸造过共晶铝硅合金组织中存在大量粗大的板条状、五瓣星状初生硅组织,严重破坏了组织,大大降低了合金的性能。目前对于过共晶铝硅合金中初生硅组织形貌控制的研究在变质处理、快速凝固等方面取得了一定的成果,但是这些方法或是效果不显著,或是技术复杂,成本高昂,不适合工业生产应用。本文系统研究了机械搅拌工艺以及液固两相区二次加热工艺对Al-30%Si合金初生硅组织的影响,提出了合适的工艺参数,制备出初生硅组织形貌较佳的Al-30%Si合金。实验表明:稳态下在一定温度机械搅拌可以显著改善初生硅组织形貌,细化初生硅组织,初生硅颗粒部分球化,棱角发生钝化,但是搅拌时间过长会使组织颗粒粗化;连续冷却的瞬态下机械搅拌,冷却速度、搅拌时间对初生硅组织形貌影响显著,在合适的工艺条件下,初生硅等效直径降至25μm,形状因子达到0.81,但若搅拌时间过长,会使熔体内杂质含量增加,组织颗粒偏聚、搭接;液固两相区二次加热可以有效的改善初生硅组织形貌,得到圆整球化的初生硅组织,初生硅等效直径28μm左右,形状因子升至0.87,分步二次加热可以改善组织的均匀性,但是如果工艺参数设置不当会使初生硅组织颗粒粗化长大;二次加热组织在三维空间中初生硅组织以球形或椭球形存在,初生硅颗粒的各个方向都有钝化。本文通过变质、机械搅拌、二次加热等手段,得到了细小、圆整、分布均匀的初生硅组织,初生硅组织形貌明显改善,本实验设备工艺简单,操作简便,效果较佳,并且成本较低,适合应用于实际生产,是一种较为有效的控制初生硅组织形貌的方法。
[Abstract]:Hypereutectic Al-Si alloy is an important casting alloy. With the increase of Si content, the wear resistance of hypereutectic Al-Si alloy is improved significantly, the thermal expansion coefficient is greatly reduced, the thermal stability is improved, the density is reduced and the high temperature resistance is improved. In the untreated cast hypereutectic Al-Si alloy there are a large number of thick plate strips and five starlike primary silicon structures which seriously destroy the microstructure and greatly reduce the properties of the alloy. At present, the research on morphology control of primary silicon in hypereutectic Al-Si alloy has made some achievements in modification treatment, rapid solidification and so on, but these methods are not effective, or the technology is complex, and the cost is high. Not suitable for industrial application. In this paper, the effects of mechanical stirring process and liquid-solid two-phase region secondary heating process on the primary silicon structure of Al-30%Si alloy were systematically studied, and the appropriate technological parameters were put forward to prepare the Al-30%Si alloy with better morphology of primary silicon structure. The experimental results show that mechanical stirring at a certain temperature can significantly improve the morphology of primary silicon, refine the primary silicon, partially spheroidize the primary silicon particles, and passivate the edges, but if the stirring time is too long, the microstructure particles will become coarse. Under the condition of continuous cooling, mechanical stirring, cooling rate and stirring time have a significant effect on the morphology of primary silicon. Under the appropriate technological conditions, the equivalent diameter of primary silicon decreases to 25 渭 m, and the shape factor reaches 0.81, but if the stirring time is too long, The secondary heating in the liquid-solid two-phase region can effectively improve the morphology of the primary silicon structure, and obtain the circular spheroidized primary silicon structure, the equivalent diameter of the primary silicon is about 28 渭 m. When the shape factor rises to 0.87, the secondary heating can improve the homogeneity of the microstructure, but if the technological parameters are not set properly, the primary silicon particles will grow and coarseness, and the secondary heating structure will exist in the shape of spherical or ellipsoid in the three-dimensional space. Primary silicon particles are passivated in all directions. In this paper, by means of modification, mechanical stirring and secondary heating, fine, round and evenly distributed primary silicon is obtained. The morphology of primary silicon is obviously improved. The experimental equipment is simple in technology, simple in operation and good in effect. Because of its low cost and suitable for practical production, it is an effective method to control the morphology of primary silicon.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21

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