【作者】 张大付；

【导师】 樊自田；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2005， 硕士

【摘要】 镁合金因密度小、比强度高,近年来在汽车、电子工业中的应用迅速增长; 消失模铸造是一种精密成型技术,它能以低的成本制造形状极为复杂的产品。为克服普通重力铸造中镁合金易氧化燃烧、成型困难的缺点,华中科技大学将消失模铸造工艺与低压浇注技术有机地结合在一起,发明了一种适于镁合金复杂薄壁铸件成型的“低压消失模铸造新技术”。本论文分析了低压消失模铸造技术的工艺原理,建立了低压消失模铸造过程中金属液充型的物理和数学模型; 在各种工艺条件下浇注了薄板窗体、阶梯模样簇、电机外壳和发动机排气管四个典型的模样和产品,用电极触点法记录了镁合金低压消失模铸造的充型过程; 试验研究了镁合金低压消失模铸造中出现的浇不足、冷隔、气孔、粘砂等典型缺陷, 分析了这些缺陷的形貌特征、形成原因及影响因素,给出了缺陷形成过程的图解模型,提出了减少和消除缺陷的工艺措施。研究结果表明:低压消失模铸造新工艺的充型能力大大高于重力消失模铸造,在重力消失模铸造中易出现的镁合金铸件浇不足缺陷,在低压消失模铸造中可以大大减少和克服; 低压消失模铸造能获得轮廓清晰的镁合金薄壁复杂铸件,它特别适合于高精度、复杂、薄壁的镁(铝)合金铸件的生产。低压消失模铸造,在可控的压力及气氛下充型和凝固,非常适合于镁(铝)合金的铸造成型特点,其充型过程、浇不足和气孔缺陷等取决于充型气压及升压速度、模样特性、浇注温度、涂层性能、真空度、铸型、浇注系统等多方面因素,需对这些工艺参数进行优化和合理的耦合来调整充型过程,最后达到消除浇不足、气孔等缺陷之目的.更多还原

【Abstract】 In the last 10 years, there is a rapid growth of application of magnesium (Mg) alloys in the auto and electronic industries because of its low density and high strength-to-weight ratio, and the lost foam casting (LFC) process is a precision forming technology capable of casting complicated parts with low manufacturing costs. In order to overcome the shortcomings of melt Mg alloy quick oxidation and mould filling difficulty, the Huazhong University of Science and Technology developed a new Low Pressure-Lost Foam Casting (LP-LFC) process for producing Mg alloy castings with thin-wall and complex geometries by combining benefits of LFC with the superiority of low pressure casting (LPC). This paper analyzes the principle of the LP-LFC process,presents the physical and mathematical models of mould filling of the new process. The patterns including window-plate, ladders cluster, electromotor frame and exhausting manifolds are poured using LP-LFC process with AZ91D alloy, and the mould filling course is tracked with electrode touch point method. Based on above tests and experiments,the casting defects including short runs, cold laps, trapped gas,metal penetration, and so on, were investigated. The appearance characteristics,birth causes and influence factors of above defects are discussed in the article,diagrammatize modes of the defects forming is also given, and the measures of reducing or avoiding defects are put forward. The investigation and practice results demonstrate that the mould filling ability of Mg alloy with LP-LFC is much better than that of LFC,and the new process can largely reduce or overcome the defects of short runs and cold laps encountered in LFC. The complex thin-walled Mg alloy (or Al alloy) castings can be produced perfectly by LP-LFC, so the new process is very suitable for casting Mg alloy (or Al alloy) parts with high precision and complex thin-walled. In LP-LFC process, the mould filling and metal freezing are carried out under the controllable pressure and gas environment. The filling course and the defects of short runs and trapped gas are mainly depended on the pressure and flux of filling gas, foam pattern property, pouring temperature, coating performance, gating system,vacuum level, etc. The various defects can be eliminated ultimately by optimizing technology data and rationally arranging those data.更多还原