金属材料在航天领域的应用及其热处理工艺

航天技术发展推动着高性能金属材料的进步以及制造技术的发展.本文对几种高性能金属材料如铝合金、钛合金、高温合金、超高强度钢、金属间化合物、镁合金以及金属磁性材料在航天领域的应用及其热处理工艺进行了简要介绍.     

化学镀制备Ni-Cu-P-TiN复合镀层及其热处理工艺

采用中温化学复合镀在高碳钢表面制备了Ni-Cu-P-TiN复合镀层,采用SEM、XRD对镀层的相组成与微观结构进行了分析,并研究了400℃热处理时间对镀层相组成、硬度、耐腐蚀性能的影响。结果表明,TiN相均匀的分散于Ni-Cu-P胞状结构的界面之间,沉积比例在4.5%~5.0%;在400℃下进行恒温热处理,随时间延长,Ni-Cu-P-TiN镀层中逐渐析出细小Ni3P相,截面硬度增加,40min时达到最高硬度960HV;随热处理时间继续延长,Ni3P相的晶粒粗化,镀层硬度下降;镀态Ni-Cu-P-TiN镀层的自腐蚀电流密度为7.92μA,仅为高碳钢(167μA)的1/20,经400℃下恒温热处理0~40min,其自腐蚀电流密度逐渐升高,40min时达到最大值28.2μA。     

航空换热器封头成形工艺分析与模具设计

通过对航空换热器封头的结构进行分析,提出不同的成形方案,最终采用分割零件,补全型面,分别拉深成形,还介绍了分型面的选择和模具设计要点。实践证明:该模具解决了零件成形难的问题,满足零件成形精度的要求。     

传热过程对多晶硅真空定向凝固过程的凝固界面及热应力的影响

以实验室10 t/a VODS型多晶炉为原型,对其凝固过程的热场、固液界面和热应力进行了瞬态模拟与实验验证。结果表明:在坩埚底部有水冷热交换块的真空定向凝固系统中硅料凝固会产生较大的热应力,增加环形保温结构使热区封闭后可改变炉内换热过程,从而改变硅料凝固情况;硅料在坩埚底部为石墨热交换块的系统中凝固时产生的热应力相对较小,但固液界面的形状会发生较大的改变,影响晶粒的生长。炉膛内径适当变宽有利于炉内热区温度分布更合理,使得硅料凝固时的固液界面更加理想。通过实验验证了多晶硅在坩埚底部无需进行水冷换热情况下进行真空定向凝固能达到冶金法生产太阳能级多晶硅的要求,这为提高冶金法制备太阳能级多晶硅质量、降低系统能耗具有一定的指导意义。     

强制对流流变成形制备7075铝合金半固态浆料及其数值模拟(英文)

采用自主研发的强制对流流变装置,研究搅拌速度对7075铝合金半固态组织的影响规律。实验结果表明,随着搅拌速度的增加,半固态组织的晶粒尺寸减小,形状因子及粒子数增加。同时,对强制对流流变成形浆料制备过程进行数值模拟,研究熔体在筒体内的流动规律和搅拌速度对合金熔体温度场和固相率的影响。模拟结果表明,合金熔体在FCR筒体内存在复杂的对流运动,熔体对流极大地改变了合金熔体温度场和固相率的分布。增加对流强度有利于减小合金熔体的过冷度梯度和改善初生晶粒的分布。     

Conditions of heat exchange in spray cooling

Technical Information

Conditions of heat exchange in spray cooling     

Determination of interfacial heat transfer coefficient and its application in high pressure die casting process

In this paper,the research progress of the interfacial heat transfer in high pressure die casting（HPDC）is reviewed.Results including determination of the interfacial heat transfer coefficient（IHTC）,influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations：（a）IHTC and casting solid fraction and（b）IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.     

Peculiar features of heat transfer under conditions of electric convection

The criterion dependencies of the Nusselt number on determining the similarity numbers for two types of electrothermoconvection (in ideal and poor conducting liquid dielectrics) for two types of electromechanical convection (in emulsions and suspensions) and for three types of electroisothermal convection (electric wind, electrization at generalized unipolar convection, and at a diffusion model) are presented. The main peculiarities of the heat transfer allowing us to calculate the heat transfer process, as well as to understand the mechanisms and regularities of the EHD phenomena, are revealed.     

Error analysis of forward and reverse heat conduction and convection calculations considering uncertainties in welding

Abstract

Numerical models of fusion welding traditionally compute temperature field for a given set of welding conditions in a forward manner. The reliability of computed temperature profile depends on the accuracy of a number of model input parameters, values of which are uncertain in nature. Here, the authors show that a genetic algorithm (GA) assisted integrated numerical model, following either convection or conduction based calculations, can identify the suitable values of the uncertain model input parameters and in turn provide reliable computed results. Powered with GA, the integrated model is used further in a reverse manner to predict multiple sets of welding conditions for a target weld geometry. The convection based calculations have been able to provide more reliable multiple welding variables in reverse calculations.     

Application of convection and infrared heat sources for mounting and demounting of electronic modules

The parameters were optimized of convection and infrared heat sources for mounting and demounting of electronic modules on printed circuit boards with surface-mounted electronic components. The modeling of the thermoprofiles of convection and infrared sources allows one to optimize the process duration and the temperature of heating of the electronic components.     

Three-dimensional turbulent weld pool convection in gas metal arc welding process

Abstract

A three-dimensional model has been developed to study turbulent fluid flow and heat transfer in a gas metal arc weld pool. The phase change process during melting and solidification is modelled using the enthalpy–porosity technique. Mass and energy transports by droplet transfer are considered through a thermal analysis of the electrode. The droplet heat addition into the molten pool is considered to be in the form of a volumetric heat source distributed in an imaginary cylindrical cavity within the weld pool ('cavity' model). A two-equation k-ε model capable of addressing turbulent weld pool convection, taking into account the morphology of the phase change, is presented. The weld pool dynamics and geometry (shape and size) in a moving gas metal arc welding (GMAW) process are studied and the effects of enhanced diffusivities on the turbulent weld pool are discussed. The predicted weld pool geometry using laminar and turbulent models is also compared with corresponding experimental post-weld sections.     

6082铝合金散热器精锻工艺分析及模具设计

分析了汽车用6082铝合金散热器的精锻成形工艺,利用Deform-3D软件对其成形过程进行模拟,结合成形过程中金属的流动规律分析,提出合理的模具设计方案。经试模生产验证,该工艺方法合理,产品质量稳定。     

Planing process of fin heat sinks

1 INTRODUCTION There are lots of traditional processes for fin heat sinks(FHS) , such as cold-extruding, weld- ing,cold-rolling and cold-forging. The cold-extru- ding process calls for strict requirements for the molds because the deformation press is very big and the machined fins are usually too thick. The welding process is complex and costly ,but not re- liable ,because the welding line is dampenedin the application,andit s easy to be damaged when two different metals electrolyze in …     

没有"万能"的材料,只有"最好"的材料--浅谈热处理技术与工艺的作用和地位

从材料科学与工程的内涵或定义出发,在简要叙述了材料合成/加工是组成材料科学与工程中4个(或5个)基本要素之一的基础上,进一步提出材料的热处理技术与工艺是改进和提高材料内在质量、从而使材料结构、组织和性质合理优化,达到材料使用效能的重要的、不可或缺的重要手段和技术措施,最后提出材料失效与否是检验材料热处理技术与工艺优劣的重要指标和发展方向.     

节能高效渗碳复合热处理工艺

重载齿轮承载大,冲击力强,要求安全性高,使用时除了应具有良的耐磨性能,还应有较高的接触疲劳强度和弯曲疲劳强度,同时具有较高的抗冲击和抗过载能力.     

In process heat input control in arc welding

Abstract

An algorithm for in process optimum heat input control of arc welding is discussed, in which an analytical model of heat conduction is used to evaluate the temperature field during welding and the convex programming method is used in the optimisation of the heat input. The thermal response calculated using an analytical model corresponds well with that measured during welding and it is possible to identify the heat efficiency using the model. Furthermore, an in process optimising algorithm which includes the real time identification of heat efficiency is examined to estimate the optimum heat input for the required temperature field in gas tungsten arc welding under conditions where there is a change in the arc length. It is ascertained that the optimising algorithm is sufficient to determine the optimum heat input in real time during welding.