γ—TiAl增压涡轮熔模铸造过程数值模拟研究

根据熔模型壳离心浇注的铸造工艺特点，建立了γ－TiAl增压涡轮凝固传热过程的数值模型，推导了离心压力下γ－TiAl金属间化合物的凝固收缩和补缩过程数学模型，模拟计算了γ－TiAl增压涡轮铸件的温度场和收缩缺陷，结果表明，模型能可靠计算γ－TiAl增压涡轮铸件凝固过程的温度分布和准确预测铸件的收缩缺陷，数值模拟结果与实验结果吻合良好，数值模拟结果证实了前期工作所提出的进一步减少及消除收缩缺陷的优化工艺措施的合理性。     

基于ProCAST研究冷却速率对新型铁基铸锭凝固过程的影响

基于Back Diffusion溶质扩散理论与CAFé模型,采用Pro CAST软件建立了?800 mm×600 mm的新型铁基铸锭铸造过程仿真模型,对选用砂型铸造过程的宏观的温度场,流场和微观组织耦合模拟;分析了凝固过程中铸件的温度场,流场和温度梯度的变化以及可能存在的缺陷;结果表明,离冷铁越近,温度梯度越大,随着冷却速度的增加,铸型充型时间减小,冷却速度为100 K/s时,充型时间为15.57 s,整个铸锭缩松缩孔的缺陷区域主要存在浇注系统以及冒口部分,且在3种冷却速度中冷却速度为10 K/s的铸锭缺陷区域面积最大,微观组织颗粒尺寸也随过冷度的增加而减小。     

低压铸造铝合金薄壁件成型压力因素模拟

采用有限元模拟仿真软件对铝合金汽车座椅骨架低压铸造工艺进行数值模拟,研究了低压铸造加压工艺中的充型压力、充型加压速率及增压压力对铸件缩松缩孔的影响.模拟结果表明:充型压力和充型加压速率的提高,有助于提高薄壁件的充型能力;对于特定的薄壁件,存在一个临界增压速率,使得缩松缩孔率最小.另外,随着增压压力的提高,缩松缩孔率减小.     

镍基高温合金熔模铸件凝固过程宏/微观多尺度模拟

建立镍基高温合金熔模铸件凝固过程的宏/微观多尺度数理模型,基于射线追踪法处理热辐射,模拟铸件的温度分布,采用三维宏/微观网格嵌套和改进的CA方法模拟微观组织,并依据微观组织模拟结果处理结晶潜热,实现微观与宏观模拟的耦合.依据等效液面下降法、Niyama判据和Darcy定律预测铸件的宏观缩孔、宏观缩松和微观缩松缺陷分布位置,并浇注实际的高温合金叶轮铸件.结果表明:模拟获得的冷却曲线、微观组织及缺陷位置与实验结果吻合良好,模拟结果能够准确预测铸件中多种缺陷的分布.     

高Nb-TiAl增压涡轮熔模铸造过程数值模拟

采用Procast铸造模拟软件模拟了两种浇注方式(顶注式与侧注式)下的Ti-45Al-8Nb合金增压涡轮重力及离心铸造工艺过程。结果显示,在重力铸造条件下,两种浇注方式均存在浇不足缺陷。侧注式较顶注式充填率高。铸件的充型率与模壳的预热温度成正比,即提高模壳的预热温度可以有效增加充型率。在离心浇注(400 r/min)时,两种浇注方式均能使金属液充满型腔。顶注式铸件的缩孔、缩松存在于增压涡轮心部,而侧注式则分布于涡轮片中,并且顶注式的缩孔、缩松缺陷体积比侧注式大很多。     

低压铸造下凝固过程缩孔缩松的预测方法研究

基于铸件铸型的传热学基础,详细研究了低压铸造下铸件缩孔缩松缺陷的形态,考虑到低压铸造补缩具有重力补缩和压力补缩双重性质的规律,以及压力对临界固相率的影响,提出了一种新的预测低压铸造下缩孔缩松预测的方法,并建立了数学模型.该预测技术基于中北大学特种液态成形技术研究中心所开发的EasyCast软件进行研究,并集成到该软件中.最后将模拟结果与实验结果进行对比,显示该模型能够较好地表现低压铸件的缩孔缩松.     

蜗轮箱盖的数值模拟及铸造工艺优化

对铸铁件涡轮箱盖进行了铸造工艺设计.根据铸件形状的特点,设计了顶注式浇注系统和3个内浇道同时对铸件浇注.利用CAD软件建立铸件的三维模型,并用View Cast铸造模拟软件对铸件的凝固过程进行了数值模拟.模拟显示,在涡轮箱盖壁与壁的连接处会产生缩孔、缩松缺陷.根据数值模拟结果并结合理论分析,对铸造工艺方案进行工艺改进.通过去除胃口和增设冷铁的方法,增加圆形区域的冷却速度.结果表明,优化后的工艺有效地消除了缩松、缩孔缺陷,从而获得了合理的铸造工艺方案.     

一种解决熔模铸件缩松缺陷的方法

针对法兰精铸件中产生的缩松,缩孔缺陷,采用数值模拟进行了分析.结果表明,采用局部冷却、局部保温营造顺序凝固条件,可以减少铸件缩松缺陷.通过加强铸件厚大部位的冷却速度,打通铸件的补缩通道,创造顺序凝固的条件,能够消除铸件缩孔、缩松缺陷.     

半固态过共晶高铬铸铁浆料在离心力作用下的凝固组织

对于倾斜冷却体法制备的半固态过共晶高铬铸铁浆料，采用离心铸造法将其制备成环形铸件，并观察和分析该铸件组织。结果表明，首先在半固态组织中初生碳化物出现偏析现象，且存在明显的偏析分界线，分界线位于距离环形铸件径向外侧面约6mm处。其次，在本试验条件下，离心力的作用只能部分消除半固态过共晶高铬铸铁组织中的缩松倾向，而且在组织中也存在缩松出现的分界线，即小于距环形铸件径向外侧面约6mm的径向区域内无缩松产生，大于距环形铸件径向外侧面约6mm的径向区域产生缩松。     

电磁离心铸件宏观组织的数值模拟

基于电磁离心凝固过程温度场的数值模拟结果,建立了铸件凝固过程物理参数与铸件凝固组织之间的定性关系,通过计算固／液界面前沿液相温度梯度Ｇ与界面生长速度Ｒ之间的比值（Ｇ／Ｒ）及冷却速度（ＧＲ）的值,对电磁离心铸件的宏观组织进行了分析,数值模拟结果与实验结果吻合良好。     

基于PTV的钛合金离心铸造物理模拟流速表征

针对钛合金立式离心铸造过程,结合粒子追踪测速技术(PTV),对相似钛合金流体充型速度进行定量表征。首先,基于物理模拟相似性原理,设计了试验模具,配置了常温相似流体;其次,进行了不同转速和浇注速度参数的物理模拟试验,并采用PTV方法获得粒子随流体运动的瞬态速度;最后分析了流体运动特征:示踪粒子会沿着与旋转速度相对的型腔壁面运动;低转速条件下适当提高离心转速和减小浇注速度有利于流体平稳充型。     

离心铸造钛合金熔体充型流动物理模拟相似理论及实验研究

借助相似物理模拟理论,研究离心铸造钛合金熔体充型流动物理模拟相似准则。并采用相似物理模拟的方法,研究离心力场下钛合金熔体充型流动过程中,熔体流动的变化规律。实验结果表明:离心力场下物理模拟钛合金熔体充型流动时,同时满足Cn准则和雷诺准则;模拟流体充型流动时,沿着横浇道后壁进行充型;流体的自由液面是以转轴为圆心的规则圆弧面;流体横截面面积随着旋转速度和充型长度的增加相应减小;转速越高,在同一时间内,充填速度和长度越小。     

Elimination of misrun and gas hole defects of investment casting TiAl alloy turbocharger based on numerical simulation and experimental study

Casting technology of thin-wall TiAl alloy turbochargers was studied by investment casting and numerical simulation.Misruns and gas holes were the main defects observed in preliminary work due to the poor fluidity of alloy,and to gas entrapment.In order to eliminate these defects,cast parameters,such as centrifugal rotation rate and mould preheating temperature,were optimized by numerical simulation,meanwhile,the structure of the shell mould was optimized to improve the filling capacity of TiAl alloy.Pouring experiments were carried out by vacuum induction melting furnace equipped with a water-cooled copper crucible based on the above optimization.The quality of the TiAl alloy casting was analyzed by fluorescent penetrant inspection and X-ray detection.The results show that a centrifugal rotation rate of 200 rpm,mould preheating temperature of 600°C,shell preparation through organic fiber addition can dramatically improve the mould filling capacity,and integrated turbochargers were finally prepared.     

Control of equiaxed grains in a complicated Cu-Ni based alloy prepared by centrifugal casting

A complicated Cu-Ni based alloy was developed to fabricate wear-resisting bush for high temperature application.The concern focuses on the control of equiaxed grains in the developed alloy ingot prepared by centrifugal casting.The results show that the equiaxed grains are determined by the pouring temperature of the melt,the cooling rate and the rotation speed of the mold.With the decrease in pouring temperature,the fraction of the equiaxed grains in the transverse section of the ingot increases and the average length of columnar grain decreases.When the pouring temperature is confined below 1,250℃,complete equiaxed grains can be obtained.Based on the optimal centrifugal casting processing,the tensile strength of the developed alloy ingot with complete equiaxed grains reaches to 810 MPa and 435 MPa at room temperature and 500℃,respectively,which is 14% and 110% higher than that of common commercial QAl10-4-4 alloy.The wear rate of the developed alloy is 7.0 × 10-8 and 3.8 × 10-7 mm3?N-1?mm-1 at room temperature and 500℃,respectively,which is 5 times and 39 times lower than that of QAl10-4-4 alloy.     

Centrifugal casting processes of manufacturing in situ functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these character-istics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg2Si particles and a portion of primary silicon particles in the inner layer, a little Mg2Si and primary silicon particles in the outer layer, and without any Mg2Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg2Si and primary silicon particles is.     

TiAl合金真空自耗熔炼过程的数值模拟

通过数值模拟研究了直径为180mm的TiAl合金铸锭的真空自耗冶炼过程,获得了TiAl合金真空自耗熔炼过程中熔炼温度、熔炼速度和冷却能力对金属熔池温度梯度、熔池形状和糊状区宽度的影响规律。结果表明,随熔炼温度升高,熔池深度增加,其形状由碗状向V形转变,熔炼温度对熔池中温度梯度和凝固前沿糊状区宽度影响较小;随熔炼速度增加,熔池中温度梯度显著减小,糊状区宽度和熔池深度则明显降低;随冷却能力增加,糊状区宽度明显减小,熔池中温度梯度和熔池深度略有减小。     

Centrifugal casting processes of manufacturing <Emphasis Type="Italic">in situ</Emphasis> functionally gradient composite materials of Al-19Si-5Mg alloy

Cylindrical components of in situ functionally gradient composite materials of Al-19Si-5Mg alloy were manufactured by centrifugal casting. Microstructure characteristics of the manufactured components were observed and the effects of the used process factors on these characteristics were analyzed. The results of observations shows that, in thickness, the components possess microstructures accumulating lots of Mg₂Si particles and a portion of primary silicon particles in the inner layer, a little Mg₂Si and primary silicon particles in the outer layer, and without any Mg₂Si and primary silicon particle in the middle layer. The results of the analysis indicate that the rotation rate of centrifugal casting, mould temperature, and melt pouring temperature have evidently affected the accumulation of the second phase particles. Also, the higher the centrifugal rotation rate, mould temperature, and melt pouring temperature are, the more evident in the inner layer the degree of accumulation of Mg₂Si and primary silicon particles is.     

离心铸造过共晶Al-Si合金自生梯度复合材料及其阻尼性能

通过改变离心铸造的转速 ,获得了内层有较多初晶Si,其余部分为共晶组织或初晶Si由外向内偏析的Al 16 %Si合金自生梯度复合材料。分析了复合材料的形成过程 ,考察了复合材料的组织 ,研究了复合材料各层的阻尼性能。结果表明 :Al 16 %Si合金自生梯度复合材料内层内耗是中、外层的 1.4倍 ,为充分发挥此材料的阻尼性能 ,应在频率高于 16 0Hz使用