华华 中中 科科 技技 大大 学学 博博 士士 学学 位位 论论 文文 摘摘 要要 随着能源和环境问题的日益突出以及人们对轿车的安全性、可靠性、舒适性等要求的提高，各大汽车制造商努力从改善汽车的结构设计和寻找新的替代材料两个方面减轻汽车的重量；不断改进和采用新的零件制造工艺提高产品的质量。铝合金具有一系列优良性能，如密度小、比强度和比刚度高、抗冲击性良好、耐腐蚀、耐磨及高的再生性等，被认为是实现轿车轻量化的首选材料。近年来，铝合金零部件在轿车中所占的比重不断增加，具有很大的开发潜力。 本文首先综述了高强度铝合金塑性成形加工工艺的国内外发展概况以及存在的问题，围绕轿车零件 7075（LC4）高强度铝合金多层杯筒形零件和中高硅铝合金SC100-T6 活塞尾的精密塑性成形新工艺的研究，采用塑性成形理论、有限元模拟和工艺试验相结合的方法，做了一系列的工作，成功地开发了安全气囊关键零件的流动控制成形工艺和活塞尾精密热模锻工艺。 分析了轿车安全气囊气体发生器关键零件的结构和形状特征，设计了两种闭式反挤压成形工艺，并分析了它们的异同；提出了以闭式挤压为变形特点的流动控制成形时金属最后充满模腔部位的判据、流动控制成形力的计算模型，并建立了成形力的计算公式；对壳体锻件流动控制成形过程进行了刚塑性有限元模拟，分析了成形过程中的应力场、应变场、速度场的分布及力-行程曲线的变化，提出了两种挤压凸模设计方案；在理论研究的基础上，对壳体和压盖进行了工艺试验，得到了优质精密锻件。 对于中高硅铝合金零件，传统的方法是采用压铸工艺生产。近年来，随着轿车性能的不断提高，要求采用塑性成形工艺制造。为了实现这一目的，作者应用Gleeble-1500 热力学模拟试验机对不同的温度和变形速率下的铝合金 SC100-T6 进行等温压缩试验，得到了合金的流动应力与成形温度、应变速率的变化规律，并应用最小二乘法建立了该种合金的本构方程。 分析了活塞尾锻件的结构和形状特征，设计了两种预锻毛坯方案；采用刚黏塑I华华 中中 科科 技技 大大 学学 博博 士士 学学 位位 论论 文文 性与热力耦合的有限元模型，对两种预锻成形及其相对应的终锻成形进行了数值模拟，对成形过程中的应力场、应变场、速度场及温度场的分布进行了分析和对比，指出优化的“V”形毛坯有利于终锻成形；根据模拟的结果，设计了预锻模、终锻模和切边模，并进行了工艺试验，锻造出了高质量的精密锻件。最后，对铝合金材料SC100-T6 进行了金相组织观测，材料锻造前成块状的初晶硅零散分布Al中，在锻造后呈细小颗粒状均匀分布。这充分体现了通过精密模锻可显著提高锻件的综合机械性能效果。 气体发生器精密锻件经太原山西锦恒汽车部件有限公司的水爆试验，其技术指标达到了美国的技术标准；该项成果已被温州市科技局列为产业化开发项目。活塞尾精密锻件超过日本同类锻件的水平，日本用户已向温岭市立华仪表厂（该项成果的委托开发方）签订大批量供货合同。这表明，这两项成果已达到了实用化水平，并将创造出显著的技术经济效益。 关键词：关键词：精密模锻 闭塞模锻 冷挤压 高硅铝合金 活塞尾 壳体 有限元方法 II华华 中中 科科 技技 大大 学学 博博 士士 学学 位位 论论 文文 Abstract Along with the energy and the environment problems increasingly outstanding, and peoples increasing requests for safety, reliability and comfortable to car, each big car manufactory makes efforts to improve the car structure design and look for new lighter material to light the cars weight, and continuously improve and adopt new advanced manufacturing technology to raise the quality of product. With a series of good performance, such as the small density, high strength ratio and rigidity ratio, good resistance to impact, corrosion and wear, high recycle etc., the aluminum alloy is thought to be the optimum materials for lighter cars. In recent years, the ratio of the aluminum alloy parts in entire car is incressing constantly, and has a very big development potential to increase. In the paper, the development and existing problems in the plastic forming technology of high strength aluminum alloy at home and abroad were summarized firstly. Based on the research of the precision die forging 7075 Al-alloy multi-layer cylinder parts and silumin SC100-T6 piston tails, a series of works have been done. The flow control forming process of the key parts in car airbags and hot die forging process of piston tails were successfully developed, adopting the plastic forming theory, FEM and experiment together. The structure and features of the key parts of the gas generator in car airbags were analyzed, and consequently two schemes of closed backward extrusion were designed. The judgment terms which the metal reaches the location of the mould cavity at the last were put forward, and the force calculating model and formula of forming force were established. The distributions of the effective stress, effective strain, velocity, and the relation between the load and the stroke were analyzed based on rigid-plastic finite element analysis, and two design schemes were presented. According to the theoretical study and result of FEM, the backward extrusion die was designed and the experiments were done successfully, and the qualified forging parts were carried out finally. Traditionally, die-cast process is applied for silumin Al-alloy parts. Due to continuously enhancement of cars performance, these components are requested to be manufactured using plastic forming process. In order to realize this target, the compression III华华 中中 科科 技技 大大 学学 博博 士士 学学 位位 论论 文文 behavior of SC100-T6 aluminum alloy was studied under the circumatance of different deformation temperature and deformation strain ratio using the Gleeble 1500 thermal stress-strain simulator. The constitutive relationship of this kind of Al-alloy was established using the least squares fit method. According to the structure and features of the piston tails part, two preforging billets were designed. The two forming schemes were simulated using thermal coupled rigig-viscoplastic finite element. With analysis and compare of the distributes of the effective stress, effective strain , velocity and temperature in the two simulation process, the conclusion was achieved that the “V” type preforging workpiece was a better design which was advantage of final forming. According to the theoretical study and FEM result, the preforging die, final die, and cutting die were designed, and the experiments have been done successfully. At last, the microstructure of SC100-T6 was analyzed, concluding that the silicon block which separates out in solidifying process of SC100-T6 alloy was broken up in the plastic forming process and scattered in Al uniformly. The result shows that plastic forming enhance the general mechanical behavior of the parts.