【作者】 彭梁锋；

【导师】 周荣；

【作者基本信息】 昆明理工大学 ， 材料加工工程， 2006， 硕士

【摘要】 半固态流变成形是目前国内外金属半固态成形研究的热点,而半固态浆料的稳定性和流变性研究是流变成型的关键之一。 本论文研究主要内容为半固态浆料在不同温度、不同时间条件下浆料性质的变化情况,半固态浆料的流变性,半固态浆料的定量保温装置的设计三个方面。 半固态浆料的保温试验研究证明,在650℃、640℃、630℃、620℃和610℃等温度恒温保温条件下,随着保温时间的延长,半固态浆料的固相分数变化不大;半固态浆料中的固相颗粒的等效直径逐渐增大,在前15分钟增长较慢,15分钟后增大加快,这是因为随着保温时间的增加,初生Si颗粒粒径分布发生变化,小直径的初生Si颗粒的百分比逐渐减小,而大直径的初生Si颗粒的百分比逐渐升高;固相颗粒的形状的圆整度逐渐变差,在前15分钟形状系数增长较慢,15分钟后有一个突然增大然后又变小的过程。在相同的保温时间内,随着保温温度的增加,半固态浆料的固相分数和初生Si颗粒直径逐渐增大,颗粒形状的圆整度变得越来越差,即浆料的半固态质量越来越差。试验结果为半固态浆料的保温参数选择提供了依据。 半固态浆料的流变性试验表明:连续冷却搅拌时,固相分数越大,合金浆料的瞬态表观粘度越大;增大剪切速率和减小冷却速率均能使合金浆料的瞬态表观粘度降低。等温搅拌时,固相分数越大,开始搅拌时瞬态表观粘度就越大,得到的稳态表观粘度也越大;冷却速度越小,表观粘度越小;合金浆料的稳态表观粘度随搅拌强度的增大有一个变小然后又变大的过程,搅拌强度在14A左右表观粘度最小。根据试验结果,在选择浆料制备和保温工艺参数时,保温温度越高,冷却速度越小,搅拌强度在14A左右时,浆料的流动性越好,充型性能也更佳。 根据半固态流变成形工业生产需要实现半固态浆料的连续和定量供给的要求,本论文设计了一套保温定量系统,可以实现半固态浆料的储存、保温和粗略定量。更多还原

【Abstract】 The semi-solid rheocasting is a hot research subject in the domestic and international academe presently, and the research on the semi-solid slurry’s stability and rheological property is crucial for the semi-solid rheocasting.The main content of this thesis involves three aspects: first, researching the microstructure changes of the semi-solid slurry hold in different temperatures for different time;second, researching the changes of the rheological property of the semi-solid slurry;third, designing an equipment for isothermal holding and rationing for semi-solid slurry.The results of the semi-solid slurry isothermal holding experiment show that only in the condition of 650℃、 640℃、 630℃ 、 620℃ or 610℃ isothermal holding, with the increasing of isothermal holding time, the volume fraction of the solid phase keep steady in the main, but the average equivalent diameter of primary silicon particles increases obviously, the increase speed is lower before 15 minutes, and faster after 15 minutes. The main reason of the change in the equivalent diameter of primary silicon particles is that the percentage of the smallness diameter primary silicon particles diminishes gradually, and the percentage of the big diameter primary silicon particles increases gradually. At the same time, the shape coefficient of the primary silicon particles increases slowly before 15 minutes, then enlarges suddenly and diminishes after the 15 minutes.With the isothermal holding temperature increasing, the volume fraction of solid phase and the equivalent diameter of primary silicon particles in the semi-solid slurry increase gradually, the shape coefficient of the primary silicon particles becomes larger, in other words, the quality of the semi-solid slurry turns worse. The results of the experiment have provided the basis for choosing the isothermal holding to the semi-solid slurry.The experiment which tested the semi-solid slurry’s rheological property showsthat in the condition of continuous cooling, the instant apparent viscosity will increase when the solid phase fraction of the semi-solid slurry increases. Increasing the intensity of the stirring and diminishing cooling rate can reduce the instant apparent viscosity of the ZL117 alloys. In the condition of isothermal stirring up, as the solid phase fraction becoming high, the instant apparent viscosity will become high when the stirring begin, and the result is that steady apparent viscosity also becomes high finally. As the cooling rate becomes low, the steady apparent viscosity becomes low;and as the intensity of the stirring increasing, the steady apparent viscosity has a change process that first becomes low and then becomes high. When the intensity of the stirring approaches to 14A, the steady apparent viscosity is the least value. According to the experiment results, when choosing the semi-solid slurry’s preparation and isothermal holding, the isothermal holding temperature should choose the high parameter, the cooling rate should choose the low parameter, and the intensity of the stirring parameter should be near to 14A. In this parameters, the fluidity and the forming ability of the semi-solid slurry is best.Basing on the need of rationing the semi-solid slurry continues for industrialization of the recasting, a suit of isothermal holding and rationing system has been designed, this system can realize the function of depositing, isothermal holding and rationing clankingly.更多还原