【作者】 杨静；

【导师】 姜巨福；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 硕士

【摘要】 近年来由于节能、减排和增效的需求，车辆轻量化越来越受到研究者的重视。越来越多的镁合金逐渐被应用在车辆行业。但是由于镁为密排六方结构，滑移系较少，所以其塑性较差。现阶段大部分镁合金采用压铸成形，虽然可以生产形状复杂的零件，但性能难以满足使用要求。而锻造成形镁合金零件虽然可以提高零件的性能，但难于变形成形形状复杂的零件。为了生产零件形状复杂而且性能好的零件，本课题提出高速充填高压密实一体化成形技术，实现高性能复杂结构件的一体化成形。首先对典型高性能复杂结构件—摩托车轮进行三维实体建模，设计浇注系统，设计三因素四水平的正交实验方案。采用商业模拟软件FLOW-3D对摩托车轮的高速充填过程进行了数值模拟，得出最佳实验参数为：浇注温度705℃，压射速度4m/s，模具温度210℃。为了技术对比分析需要，采用压铸与高速充填高压密实一体化成形两种技术在相同工艺条件下分别成形摩托车轮结构件。结果表明，压铸成形件容易出现表面缺陷，例如充不满、气孔、冷隔和裂纹等。与压铸实验对照，铸锻零件表面缺陷较少。不同轮辐的常温拉伸实验表明，锻造力的存在可以大幅度的提高轮辐的力学性能。抗拉强度从151Mpa提高207Mpa，延伸率从6.3%提高到9.9%。高温拉伸的抗拉强度与延伸率也比常温拉伸有所提高。从断口扫描照片可以看出，断裂方式由脆性断裂向韧性断裂过渡。而且与压铸件相比，利用高速充填-高压密实方法成形的结构件的维氏硬度值也明显提高。微观组织表明，压铸件晶粒大小不均匀，平均晶粒尺寸为60um,存在尺寸为160um的粗大枝晶，且有气孔、氧化夹杂、裂纹等缺陷。铸锻件晶粒比较均匀，平均晶粒尺寸为20um，组织比较均匀致密。从透射结果可以看出，变形存在孪晶，且锻造力的存在使孪晶间距变小，孪晶厚度也变小。从EBSD结果看，铸锻件的晶粒较小，取向较小，同时织构变少。综合以上分析可见，利用高速充填高压密实一体化成形成形的结构件无论在力学性能还是微观组织形貌上较压铸成形件都有明显提高和改善。这同时说明高速充填高压密实一体化成形是一种适合成形高性能负责形状结构件的近净成形技术。更多还原

【Abstract】 In recent years, light weight of vehicle is paid more and more attention due torequirements for saving energy, saving emission and increasing efficiency. More andmore magnesium alloys have been widely used in vehicle industry. It is difficult todeform magnesium alloys plastically due to the hexagonal close-packed crystal structureand limited slip system. At present, most magnesium alloys are produced by die casting.Although die casting can produce complex components, mechanical properties of theformed components cannot meet application requirements.On the other hand, forging can form components with enhanced mechanical properties,but the shape for the components cannot be too complex. In order to realize theintegration forming of the complex components with enhanced mechanical properties, anovel integral forming called high-speed filling and high-pressure density is proposed,in which combines the advantages of the die casting and forging.Firstly, three-dimensional model of typical complex motorcycle wheel componentwith enhanced mechanical properties was carried out. At the same time, gating systemand a three-factor and four-level orthogonal experiment were designed in this research.Numerical simulation of high-speed filling process was done by using FLOW-3Dsoftware and optimal process parameters including pouring temperature of705℃,injection speed of4m/s and die temperature of210℃were achieved.Die casting and the technology of high-speed filling and high-pressure densifyingwere employed to form the motorcycle wheel components under the same conditions inorder to compare them. The results show that a large number of surface defects such asincomplete filling, pores, cracks and cold shuts were found in the components formedby die casting. However, high surface quality was obtained in the components formedby high-speed filling and high-pressure densifying. The results of spoke tensile tests atroom temperature indicate that the mechanical properties of spokes have beensignificantly improved due to the application of forging force. The average tensilestrength increases from151Mpa to207Mpa, and the average elongation rises from6.3%to9.9%. The mechanical properties at high temperature are also increased. SEMobservation of fractograph shows that fracture mechanisms have been changed frombrittle fracture to ductile fracture. Furthermore, Vickers hardness of components formedby high-speed filling and high-pressure densifying was significantly improvedcompared with die castings.The microstructure of components formed die casting is not very uniform and theaverage grain size of microstructure was60um. Some oxide inclusions, cracks, holes,dendrites with an average grain size of160μm were found in the microstructure of die castings. On the contrary, fine, uniform and dense microstructure was obtained in thecomponents formed by high-speed filling and high-pressure densifying and the averagegrain size was20um. TEM results shows that some twins were created during theforming process. Furthermore, the space and thickness between two twins decreasebecause of the existence of forging force. From the EBSD results, we find that thehigh-speed filling and high-pressure densifying make the grain size and misorientationangle small, and texture reduced.Above all，an important conclusion can be drawn that the mechanical propertiesand microstructure of components formed by high-speed filling and high-pressuredensifying were significantly improved compared to die castings. It illustrates thathigh-speed filling and high-pressure densifying is suitable for forming complexcomponents with enhanced mechanical properties.更多还原