铝合金挤压铸造过程界面的传热行为

通过测量挤压铸造过程的温度变化,采用基于非线性估算法的热传导有限元反算模型,求解不同挤压力下的界面传热系数(IHTC)。利用铸件中心模拟温度与测量温度验证模型的准确性;结合铸件表面和中心测温点温度变化讨论重力条件和挤压力条件下界面传热系数的变化规律,发现挤压力有效地增加了界面传热系数的峰值和稳定值。探讨挤压力对界面气隙的影响,对于ZL101A铝合金直接挤压铸造过程,MPa挤压力具有较好的挤压效果。     

A319合金挤压铸造凝固过程数值研究

利用ANSYS有限元分析软件,考虑相变潜热、对流边界条件和界面传热系数等因素,建立了铝合金挤压铸造凝固过程温度场模型,研究了挤压铸造过程参数(挤压力及模具预热温度)对铸件凝固过程温度分布的影响.通过分析不同挤压力下铸件的显微组织,表明模拟结果与实验结果基本一致.     

基于Magmasoft的汽车前叉压铸成型数值仿真

分析了A357铸造铝合金汽车前叉铸造成型工艺,运用Magmasoft专业铸造有限元分析软件建立了其压铸成型仿真模型。分析了充型过程的压力分布,分析了铸件结构对熔融金属流动及铸件温度的影响,研究了铸件凝固冷却应力分布及缩孔、缩松。结果表明:随着充型率增加,压力最大值也逐渐增加,不同充型率下的压力不同;铸件结构对熔融金属流动影响较大,对铸件温度影响较小;凝固冷却应力主要集中在复杂部位;随着凝固分数增大,缩孔、缩松率逐渐增加。     

不同铸型铸造凝固过程温度场的有限元模拟

利用有限元方法,采用阶梯试块,对ZL105合金的砂型铸造和金属型铸造的凝固过程中的温度场进行了有限元模拟.结果表明,砂型铸造时铸件冷却速度慢,铸件内温度梯度小,最后冷却的部位在铸件的最大尺寸处,铸型与铸件界面处的温度较高.金属型铸造时铸件冷却速度快,铸件内温度梯度大,最后冷却的部位偏离铸件的最大尺寸位置一定距离,铸型与铸件界面处的温度较低.     

ZL201铝合金铸件凝固过程温度场的有限元模拟

以矩形ZL201铝合金铸件压力铸造为例,对凝固过程进行了合理的假设和简化,利用有限元方法,对铸造凝固过程温度场宏观变化进行了模拟计算,获得了铸型与铸件在凝固过程中的温度分布规律。在凝固过程中,铸件温度一直呈下降趋势,铸型温度的变化趋势是先升高后降低。计算结果表明,三维温度场的数值模拟能够反映铸件冷却过程温度场的动态变化,为提高铸件质量、确定凝固时间和优化工艺参数提供了参考。     

Al-7Si-Mg铝合金挤压铸造过程热-力行为的研究

采用了0.1、50、75和100 MPa压力对Al-7Si-Mg合金进行直接挤压铸造,对铸型内温度和压力变化进行了测试,讨论了两者之间的关系以及压力变化对收缩缺陷形成的影响。同时,计算了凝固过程铸件和模具界面摩擦力。结果表明,外挤压力对界面摩擦力和压力传递有重要作用。     

K4169铸件凝固温度场及晶粒组织计算机模拟

研究了在PRO/E和ANSYS软件环境下对复杂铸造系统进行联合建模的方法,采用PRO/E构建K4169高温合金壳体铸件,导入ANSYS软件构建铸造系统并对其凝固过程中的温度场进行模拟,得到铸件各点温度随时间的变化规律及其温度场的分布特征。根据铸件中各特征点的冷却曲线,采用非连续形核模型获得晶粒组织特征值,基于元胞自动机的方法实现镍基高温合金铸件关键部位凝固组织演变过程的可视化仿真。模拟结果与实测晶粒组织符合较好。     

铁模覆砂工艺的砂层厚度对球墨铸铁件冷却速度的影响研究

针对采用铁模覆砂工艺生产厚大球墨铸铁铸件过程中出现的附铸试块基体组织珠光体含量超标的问题,采用计算机模拟的方法分析了该铸件的凝固过程,找出冷却速度差异较大部位。通过砂层厚度的调整改善不同部位的冷却条件,实现对铸件组织的控制,很好地解决了附铸试块基体组织不满足要求的问题。定量分析了砂层厚度的增加对冷却速度的影响,分析数据可为铁模覆砂铸造生产同类型产品提供参考。     

THERMOMECHANICAL MODELING OF SOLIDIFICATION PROCESS OF SQUEEZE CASTING I. Mathematic Model and Solution Methodology

开发了模拟挤压铸造凝固过程中铸件温度、应力及形状变化的有限元模型. 该模型包括了凝固过程中潜热的释放和体积收缩效应、界面传热和变形的相互作用以及凝固壳在冲头压力下的变形等. 应力场模拟中采用热弹粘塑性本构模型描述凝固壳的变形, 并对液相和糊状区进行了特殊处理. 利用接触算法处理铸件与模具界面, 并且采用一种特殊的迭代法来模拟冲头的运动. 该模型可以用来研究模具设计和工艺参数(如模具温度及冲头压力等)对铸件质量的影响.     

挤压铸造过程热-力耦合分析的有限元模型

开发了模拟铝合金挤压铸造凝固过程铸件温度、应力及形状变化过程的有限元模型。该模型包括了凝固过程的潜热释放和体积收缩效应、传热和变形通过界面气隙的相互作用、以及凝固壳在冲头压力作用下的变形过程等。应力场模拟中采用热弹粘塑性本构模型来描述凝固壳的变形,并对液相/糊状区进行了特殊处理。利用接触算法处理铸件与模具界面,并且采用一种特殊的迭代法来模拟冲头的运动。该模型可以用来研究模具设计、工艺参数(如浇注温度、冲头压力、加压时间等)对铸件质量的影响。     

Experimental and numerical analysis of effect of cooling rate on thermal–microstructural response of spheroidal graphite cast iron solidification

This work presents an experimental and numerical study of the solidification process of an eutectic spheroidal graphite cast iron (SGI). The effect of the cooling rate on the thermal–microstructural response is particularly analysed. To this end, experiments as well as numerical simulations were carried out. The experiments consisted in a solidification test in a wedge-like casting such that different cooling rates were measured at specific positions along the part. A metallographic analysis was also performed in five locations of the sample with the aim of obtaining the number and size of graphite nodules at the end of the process. The numerical simulations were made using multinodular based and uninodular based models. These two models predicted similar results in terms of cooling curves and nodule counts. Besides, good experimental–numerical agreements were obtained for both the cooling curves and the graphite nodule counts.     

Experimental determination of heat transfer coefficients during squeeze casting of aluminium

Heat transfer coefficients during squeeze cast of commercial aluminium were determined, by using the solidification temperature versus time curves obtained for varying applied pressures during squeeze casting process. The steel mould/cast aluminium metal interface temperatures versus times curve obtained through polynomial curves fitting and extrapolation was compared with the numerically obtained temperatures versus times curve. Interfacial heat transfer coefficients were determined experimentally from measured values of heating and cooling temperatures of steel mould and cast metal and compared with the numerically obtained values and found to be fairly close in values. The values of the heat transfer coefficients were found to increase with increase in applied pressures and to decrease with fall of solidifying temperatures corresponding to three distinct solidification stages namely, liquidus, liquidus–solidus and solidus stages. Below temperatures of 500 °C, the effect of the increase in heat transfer coefficients with applied pressure application becomes less significant and the drop in values of the heat transfer coefficients with solidification temperatures at any applied pressures remains fairly constant. The peak values of heat transfer coefficients obtained for as-cast (no pressure application) and squeeze cast (pressure application) of aluminium are 2975.14 and 3351.08 W/(m² K), respectively. Empirical equations, relating the interfacial heat transfer coefficients to the cast aluminium surface temperatures and applied pressures at three distinct temperature range intervals, were also derived and presented.     

基于AnyCasting的挤压铸造铝合金机座工艺研究

针对铝合金机座零件的结构和挤压铸造工艺特点,对原超慢速压铸模具的进浇方式、排溢系统、冷却系统进行再设计,使其适用于挤压铸造。利用AnyCasting软件,对修改前后的模具进行模拟分析对比,修改前模拟分析的产品内部缩松缺陷与实际情况一致,修改后的模具通过更改进浇方式,扩大排气槽及溢流槽,使气体在液流充填模具型腔过程中能顺利排出;并增加冷却水路来控制模具温度,保证产品在冷却过程中实现顺序凝固,进而消除产品的内部缩松缺陷。所获得的挤压铸造铝合金支座铸件组织致密,可进行T6热处理,力学性能接近锻件性能。     

Simulation on solidification structure of 72A tire cord steel billet using CAFE method

The solidification microstructure has an important effect on the mechanical properties of castings.Therefore,an FE (Finite Element) CA (Cellular Automaton) coupling model was developed for the simulation of solidification structure during the continuous casting process of 72A tire cord steel.In the model,the effect of phase transformation (l→g→a) during solidification was considered based on a thermodynamic database.The effect of electromagnetic stirring (EMS) was determined by increasing both the thermal conductivity and crystal formation rate in the liquid phase.The results show that the cooling curves and solidification structure calculated by this model agree well with the experimental results.The optimum pouring temperature range for tire cord steel casting was also discussed based on the present model.By comprehensive consideration of billet quality and smooth production,the pouring temperature should be controlled at about 1,495℃ under the casting conditions of the local plant in this study.     

Progress on modeling and simulation of directional solidification of superalloy turbine blade casting

Directional solidified turbine blades of Ni-based superalloy are widely used as key parts of the gas turbine engines.The mechanical properties of the blade are greatly influenced by the final microstructure and the grain orientation determined directly by the grain selector geometry of the casting.In this paper,mathematical models were proposed for three dimensional simulation of the grain growth and microstructure evolution in directional solidification of turbine blade casting.Ray-tracing method was applied to calculate the temperature variation of the blade.Based on the thermo model of heat transfer,the competitive grain growth within the starter block and the spiral of the grain selector,the grain growth in the blade and the microstructure evolution were simulated via a modified Cellular Automaton method.Validation experiments were carried out,and the measured results were compared quantitatively with the predicted results.The simulated cooling curves and microstructures corresponded well with the experimental results.The proposed models could be used to predict the grain morphology and the competitive grain evolution during directional solidification.     

采用正交设计优化单晶合金定向凝固数值模拟参数

采用正交设计方法研究单晶高温合金定向凝固过程数值模拟所需参数对温度场和冷却曲线的影响.结果表明:单晶高温合金凝固曲线对模拟参数十分敏感,特别敏感于铸件与铸型之间的界面换热系数.通过正交设计获得边界条件参数使模拟结果与试验结果吻合良好.确定符合DD6单晶高温合金凝固过程的数值模拟边界条件.     

熔模铸件凝固过程冷却曲线的测量方法

熔模铸件凝固过程冷却曲线对ProCAST模拟参数的反算求解和优化有重要作用。通过对熔模铸钢件凝固过程冷却曲线的测量方法进行研究并确定铸件内部冷却曲线的测量方法,试验测试出了精度较高的铸件冷却曲线。     

Section thickness-dependent tensile properties of squeeze cast magnesium alloy AM60

The development of alternative casting processes is essential for the high demand of light weight magnesium components to be used in the automotive industry,which often contain different section thickn...     

挤压铸造半固态A356铝合金的组织与力学性能

采用低温铸造方法制备A356铝合金半固态坯料.在200 t立式油压机上用挤压铸造方法将A356铝合金半固态浆料挤压成件.研究挤压铸造件的微观组织、力学性能,并与液态挤压铸造件进行比较.结果表明,A356铝合金半固态挤压铸造件组织由球形及椭圆形α-Al晶粒和α+Si共晶成分组成,且制件充型完整、无宏观缩孔、组织致密.在比压48.7 MPa,浇注温度575℃,保压时间3s条件下成形的半固态挤压铸造件的抗拉强度、屈服强度、伸长率分别达到278 MPa、225 MPa、13.2％,相比于在比压48.7 MPa,保压时间3s,710℃液态挤压铸造件性能分别提高了8.6％、8.2％、24.5％.A356铝合金半固态挤压铸造成形件具有较高的综合力学性能.     

The relationship between cooling rate and the structure and properties of hypo-eutectic cast iron

The aim of the present work is to make a correlation between the cooling rate of grey cast iron during solidification and the resulting structure, phases and mechanical properties. Liquid cast iron with a carbon equivalent of 3.92% was cast in sand moulds. Different cooling rates were obtained by changing the casting shape and thickness.

The cooling curves were recorded using a data acquisition system in order to determine the solidification parameters. Some samples were reheated to a temperature above solid state transformation—austenitised (1118 K) and then quenched.

The microstructure was studied in order to determine the phases formed such as graphite, pearlite, ferrite and cementite. Their shape, size and volume fractions were studied. The formation of these phases was correlated with the cooling and solidification parameters. Some mechanical properties, namely hardness and tensile properties, were measured.

Correlation between these properties cooling rate and microstructure parameters are presented.