近液相线铸造过程中近球形α相的形成机理

为从理论上弄清近液相线半连续铸造过程中铝合金半固态组织形成的基本规律和机制,研究了浇注温度、铸造速度和冷却强度等工艺参数对6061合金初生α相演变的影响,根据金相检测和多尺度计算机模拟结果,分析了近球形α相的形成机理.实验发现,在浇注温度为657℃、铸造速度为150 mm/min、冷却水流量为0.05 m3/min时可...     

4045/3004/4045层状铝合金复合材料连铸制备方法

本文旨在开发出制备复合锭坯的新技术,在新型热顶石墨环结晶器中安装冷却板,采用直接水冷半连续铸造法实现了4045/3004/4045铝合金三层复合锭的实验室制备,研究了复合锭坯的宏观形貌、微观组织,并考察了界面两侧元素分布以及铸造过程中界面附近3004合金熔体的温度分布.结果表明:在冷却板的作用下界面附近形成了一层温度分布较为均匀的固态支撑层,从而保证复合铸造过程的顺利实现,复合界面结合较好,且为一种冶金结合;由界面抗拉强度测试结果可知界面的结合强度均高于96 MPa,进一步证明了两种合金的结合是一种冶金结合.     

铝合金半连续铸造网络监控系统构建研究

铝合金半连续铸造含有许多地理分散的子系统,它需要建构一个网络系统为管控生产过程与进行综合自动来创造条件。所以我们就有必要来对铝合金半连续铸造的生产过程进行网络监控系统进行研究。通过分析铝合金半连续铸造生产技术的提升以及网络监控的设计要求后,对系统的总体的设计进行构想与并提出一种结合现场总线与以太网的混合式铝合金半连续铸造网络监控系统。     

某种钛合金精密成形铸件铸造变形的数值模拟

目的 基于ProCAST,建立钛合金铸件铸造变形的模拟预测方法。方法 以某板状钛合金铸件为例,模拟了充型凝固、型壳内冷却和脱壳后冷却3个过程,并分别对各过程进行了相应假设和参数设置。为验证模拟结果,根据模拟模型设计了浇注验证实验。结果 铸件中间部位向外侧凸起,加强筋部位向内侧凹陷,和实验结果基本一致,变形量预测吻合度在60%~72%之间。结论 通过合理设置模拟流程和材料参数模型,数值模拟可以预测钛合金铸件的变形规律,并为变形量预测提供重要参考。     

7050铝合金半连续铸造扁锭用水量计算

铝合金半连续铸造用水量准确计算直接确定生产效率与生产质量，大面水量与小面水量合理分配是铸锭内部拉应力均匀。     

Mn57-2-2-0 . 5 锰黄铜铸造裂纹成因分析及对策

以Mn57-2-2-0.5锰黄铜半连续铸造生产实践为例,分析了试制过程中产生裂纹的原因,通过结晶器结构优化、冷却水强度分配及浇注速度调整等措施,解决了该类缺陷。此工艺措施对同类合金的同类缺陷非常有效,同时对探索复杂黄铜半连续铸造生产有一定借鉴意义。     

ZL201合金液相线铸造组织与成形性能

研究了近液相线半连续铸造ZL201合金的微观组织及其在二次加热过程中的变化.在液相线温度下半连续铸造的ZL201合金组织为均匀、细小的蔷薇状组织,晶粒的平均等积圆直径为43.6μm,晶粒平均圆度为1.88.经二次加热后,铸造组织逐渐转变为等轴晶.在620℃下加热20min后,晶粒平均等积圆直径为111μm,晶粒平均圆度1.42.在640℃下加热20min后,晶粒平均等积圆直径为108μm,晶粒平均圆度1.58,半固态压铸件硬度可达到116.6HV.结果表明,液相线半连续铸造可以获得理想的半固态坯料.     

强制冷却对大型铸钢件组织与性能的影响

采用模拟装置铸造了φ70×300毫米的砂型试样和强制冷却试样。利用电子计算机进行数值模拟,计算出两类试样在凝固过程中的温度梯度 G、凝固速度 R 以及 G/R 的比值,强制冷却使大型铸钢件的细晶区扩大,柱状晶区向内转动,粗大等轴晶区减少。与传统观念相反,发现适宜的强制冷却可以使魏氏组织具有很高的冲击韧性。     

基于多元非线性回归分析的Cu-Ag合金偏析预测模型研究

目的研究Cu-Ag合金金属型铸造过程中,铸造工艺对宏观偏析的影响规律。方法通过数值模拟技术和实际浇注试验,对Cu-Ag二元合金金属型铸造过程中的宏观偏析缺陷进行分析,研究主要凝固参数,即冷却速率和温度梯度对宏观偏析程度的影响规律。在此基础上,利用多元非线性回归分析方法对所获得数据进行分析,明确主要凝固参数与宏观偏析程度之间的定量关系,建立Cu-Ag合金金属型铸造过程中的宏观偏析预测模型。结果采用研究获得的最佳浇注工艺方案,即浇注温度为1100℃、浇注时间为120 s、铸型温度200℃、涂料厚度为1.5 mm进行实际浇注,所获得铸件中的宏观偏析缺陷得到了明显的改善。结论降低浇注速度可以有效提高冷却速度和温度梯度,从而有效减小宏观偏析的倾向。     

ZL201合金液相线铸造与二次加热的合金组织

为了研究半固态金属的成型规律,采用电子显微镜及图像分析仪,研究了近液相线半连续铸造ZL201合金的微观组织及其在二次加热过程中的变化.研究表明,在液相线温度下半连续铸造的ZL201合金组织为均匀、细小的蔷薇状组织,晶粒的平均等积圆直径为43.6μm,晶粒平均圆度为1.88.经二次加热后,铸造组织逐渐转变为等轴晶.在620℃下加热20min后,晶粒平均等积圆直径为111μm,晶粒平均圆度1.42.在640℃下加热20min后,晶粒平均等积圆直径为108μm,晶粒平均圆度1.58.研究表明,近液相线半连续铸造可以获得理想的ZL201合金半固态坯料.     

Ti-6Al-4V熔模精密铸造充型及凝固过程计算机模拟

应用自行开发的基于微机上运行的铸件凝固 /充型计算机模拟软件 ,对Ti-6Al-4V钛合金薄壁件精密铸造的充型及凝固传热过程进行了模拟分析 .应用自行安装的多通道钨铼热电耦温度数据计算机采集、分析系统 ,测定了该钛合金起吊接头精密铸件的凝固冷却曲线 ,获取了该合金有关的凝固参数 .对包括上述零件在内的钛合金薄壁件精密铸造的充型过程及凝固传热的温度分布进行了数值模拟 ,模拟计算与实测结果合理吻合 .基于该研究可对其精密铸造工艺进行优化设计 .     

An Effective Inverse Heat Transfer Procedure Based on Evolutionary Algorithms to Determine Cooling Conditions of a Steel Continuous Casting Machine

The inverse modeling of heat transfer is a useful tool in analyzing contact heat transfer at the ingot surfaces during the continuous casting process. The determination of the boundary conditions involves an experimental work consisting in the evaluation of the thermal history, generally at the casting surface, experimentally provided by infrared pyrometers. Additionally, numerical simulations, based on the solution of the 2D transient heat conduction equation, are performed in order to be inversely solved in response to the measured thermal data furnished by the sensor. Due to computational time consumption during simulations in searching cooling conditions, this work proposes an interaction between natural inspired algorithms, called evolutionary algorithms, and the numerical model in order to speed up the searching process. The present work aims to compare three algorithms, namely genetic algorithm, improved stochastic ranking evolutionary strategy, and evolutionary strategy with Cauchy distribution. The latter develops a metaheuristic version of an evolutionary strategy workflow, using a Cauchy random number function to generate each individual, instead of the usual uniform distribution function available in almost all programming languages. The surface temperature, solid shell, and molten pool profiles from the determined cooling conditions are analyzed in terms of casting quality.     

Heat Transfer between Casting and Die during High Pressure Die Casting Process of AM50 Alloy-Modeling and Experimental Results

A method based on die casting experiments and mathematic modeling is presented for the determination of the heat flow density （HFD） and interfacial heat transfer coefficient （IHTC） during the high pressure die casting （HPDC） process.Experiments were carried out using step shape casting and a commercial magnesium alloy,AM50.Temperature profiles were measured and recorded using thermocouples embedded inside the die. Based on these temperature readings,the HFD and IHTC were successfully determined and the calculation results show that the HFD and IHTC at the metal-die interface increases sharply right after the fast phase injection process until approaching their maximum values,after which their values decrease to a much lower level until the dies are opened.Different patterns of heat transfer behavior were found between the die and the casting at different thicknesses.The thinner the casting was,the more quickly the HFD and IHTC reached their steady states.Also,the values for both the HFD and IHTC values were different between die and casting at different thicknesses.     

Simulation analysis of thermal stress during casting process of large-sized alloy steel ingot

To quantitatively analyze the main reasons of common crack in the surface of alloy steel ingot with 5% Cr during production and to propose the direction of improvement, a physical model system, which consisted of steel ingot mold, casting, riser of heat insulation, slag layer, sprue pipe, and runner, was primarily established by three-dimensional CAD software. The joint simulation method concerned with pouring, solidification, temperature field, and cast stress was determined by using ADSTEFAN cast simulation software. The stress distribution of casting and the quantitative effect of shake-out timing were analyzed in detail. An effective plan of decreasing stress was proposed in cooling mode.     

Determination of boundary condition of a multi-crystalline silicon billet during continuous casting

Boundary conditions are always complicated and not readily available during continuous casting, especially for the multi-crystalline silicon materials. In order to improve the situation, the temperature variation curves for certain points in the multi-crystalline silicon have been obtained using the experimental apparatus under different cooling conditions. Based on the temperature measurements, the heat transfer coefficients in the second cooling zone and the interface between the multi-crystalline silicon and mould or bottom block have been calculated applying the inverse method and numerical simulation. The calculated results have been validated by comparing the predicted temperatures with the measured ones.     

An inverse finite element minimization-based method for solution of multi-dimensional phase-change and material boundary shapes

An inverse finite element method for solution of unknown multidimensional phase-change and material boundary shapes is presented. The method is based on minimization and requires boundary shape parametrization. The unknown boundary parameters are determined by minimizing the error between a limited number of known (e.g. measured) temperatures and the temperatures associated with the iteratively altered boundary. The algorithm presented is based on the multidimensional downhill simplex minimization method. The inverse method is illustrated and verified using a model of the plasma arc welding process. In particular, it is shown that the technique is capable of accurately determining a specified weld pool capillary interface shape using a limited number of simulated thermocouple measurements. The code's ability to determine the interface shape is investigated under various interface-thermocouple separations, using varying numbers of simulated thermocouples.     

Modelling the pressure die casting process with the boundary element method: Steady state approximation

This paper describes a model which can predict the temperatures on the cavity surfaces of a die. The time varying boundary conditions are averaged so that the process can be modelled as a steady state problem. Since the model considers only thin components, it is reasonable to assume that the melt has totally solidified before ejection, and therefore the quantity of heat energy entering the die over the casting cycle can be estimated. This and other assumptions relating to the boundary conditions also enable the value of thermal resistance between the melt and the die to be estimated. Under certain conditions, subcooled nucleate boiling takes place in the cooling channels of the die. An iterative procedure is used to take account of this, which involves the repeated calculation of global heat transfer coefficients for the cooling channels, with the criteria that the total energy transferred through the channels is equal to that transferred due to boiling and convection. The boundary element method is used to predict the cavity temperatures. In die casting, only the temperatures on the cavity surfaces are of interest since the surface quality of a component is related significantly to the temperature distribution over the cavity. Since only thin components are considered herein, it is not necessary to model the solidifcation process and discretize the cast. These factors make the BEM ideally suited for the work described in this paper. To verify the model, the predicted temperatures for two components are compared with experimental values measured using thermocouples and a thermal imaging camera. It was found that there is fairly good agreement between the two sets of results.     

Quantitative metallographic assessment of the electromagnetic casting influence on the microstructure of 7075 Al alloy

This study presents an attempt to obtain the better quality of an aluminum super-high strength alloy by application of electromagnetic field during the casting process. The conventional continuous casting process of aluminum alloys causes many defects, such as surface imperfections, grain boundary segregation, non-uniform grain size, and porosity. The better ingot surface along with the homogeneous fine-grained microstructure, and hence the better mechanical properties of the ingot, can be achieved by applying the electromagnetic casting process. The microstructure characterization, accompanied by quantitative metallographic assessment, reveals that it is possible to avoid or decrease many defects of as cast ingots during electromagnetic casting process. In this article, the microstructure of the samples of as cast 7075 aluminum alloy, obtained with and without electromagnetic field influence, was analyzed by optical microscope and the variation of key alloying elements content, i.e., Zn and Mg, through the ingot cross section was examined by chemical analysis. Besides, the microstructural parameters such as dendrite arm spacing, interdendritic space width, as well as eutecticum and intermetallic phases volume fraction, were measured using linear method. The electromagnetic field influence on the microstructure of the as cast 7075 Al alloy was evaluated based on measured quantitative metallographic data.     

Near net shape processing of metal and ceramic composite ingot mould

Abstract

A new pressureless infiltration method was developed to place a silicon dioxide particle reinforced layer on the surface of an industrial ingot mould without changing the production process of the ingot mould. The morphology and structure of the composite layer were investigated by optical and scanning electron microscopy. The service life and thermal characteristics of the reinforced mould were tested during their use in practical casting processes. It was found that a 4 mm thickness composite layer can be obtained on the surface of an ingot mould with this method. The reinforced mould can be used directly without any extra machining process. The service life of the new mould is twice that of the original for the same application conditions. The heat resistance and wear resistance of the mould were evidently improved.