基于近似因子分解法和SPH法的医用挤压铸件充型模拟

采用近似因子分解法、光滑粒子流体动力学法进行挤压铸造充型过程数值模拟研究。模拟结果显示,近似因子分解法、光滑粒子流体动力学法(SPH)计算结果与Win-cast铸造模拟软件计算结果基本一致,从而验证了两种方法的有效性和准确性。由于SPH的粒子携带材料性质,能够在空间中运动,较传统的有限差分法而言,不存在自由表面和运动物质交界面等的位置难以精确确定的问题,在数学模型的建立方面具有一定优势。     

高合金钢过饱和固体渗碳的计算机模拟

本文讨论了高合金钢过饮和渗碳过程,提高了计算高合金钢固体渗碳的碳浓度分布的数学模型,以此模型对3Cr13和Cr10固体渗碳的碳浓度分布进行了计算机模拟。模拟结果与相应的实验结果基本吻合,表明了本文的数学模型及方法是可行的。     

高合金钢固体渗碳及渗层扩散的计算机模拟

讨论了高合金钢固体渗碳和渗碳后渗层的扩散处理,提出了计算高合金固体渗碳及渗件表面不发生脱碳情况下渗层扩散处理的碳浓度分布的数学模型,以此模型对3Cr13和Cr10钢固体渗碳和渗层扩散处理的碳浓度分布进行了计算机模拟。模拟结果与相应的试验结果基本吻合,表明了本文的数学模型及方法是可行的。     

基于有限差分法和光滑粒子法的镁合金充型模拟

针对Benchmark件,采用有网格方法(FDM)和无网格方法(SPH)进行充型过程数值模拟,并将模拟结果与WinCast计算结果进行了比对,从而验证了两种方法的有效性和正确性。由于SPH方法可通过追踪粒子的运动得到整个物理系统的特性,无需采用专门方法确定自由表面,在数学模型上具有一定优势。     

超音速电弧喷涂粒子速度的计算机仿真

粒子速度对涂层质量有重要的影响,计算机仿真是确定粒子运动规律的有效方法。通过建立数学模型,对超音速电弧喷涂纯铝的粒子速度进行了仿真计算,结果表明,粒子飞行过程中经历了一个加速减速的过程,直径40μm的粒子最大速度为365m／s,最大速度点离喷嘴出口52mm,试验测得的粒子最大速度为386m/s,位置在喷嘴出口40～60mm范围内。仿真计算反映了射流中粒子的运动特征,从理论上证明超音速电弧喷涂的粒子速度超过音速。     

Al-In难混溶合金的液相分离过程及显微组织数值模拟

建立了一个描述Al In难混溶合金冷却过程中液—液相变区微观组织演化过程的数学模型。该模型综合考虑了第二相液滴的形核、扩散长大、Brownian碰撞和运动碰撞的共同作用 ,并对模拟的结果进行了可视化动态模拟研究。以Al 3 0 %In合金为例进行模拟 ,结果表明 ,第二相在断面上的体积分数、粒子大小及分布与实验结果基本一致。这说明建立的模型对Al In难混溶合金具有一定实际预测功能。     

碳钢的渗钛模型

本文从Fick第二扩散定律出发,建立了适用于气体或固体渗钛的数学模型,并通过碳钢的固体渗钛实验进行验证。结果表明,该数学模型与实验结果拟合性好,能用来描述碳钢的渗钛过程。     

基于SPH法的AZ31镁合金ECAP过程数值模拟

引入一种新的无网格法——光滑粒子流体动力学法(Smooth Particle Hydrodynamics,SPH),将问题域离散为一系列粒子,避免了由于网格的划分导致计算精度下降。通过建立数学模型并编写SPH方法程序,对AZ31镁合金ECAP过程在高挤压速度下的裂纹萌生和扩展进行数值模拟,并将模拟结果与有限元模拟结果及试验结果进行对比,验证了所建SPH程序的准确性及可行性。     

9Cr2Mo冷轧辊加热过程的数值模拟

利用有限元数值方法模拟了９Ｃｒ２Ｍｏ冷轧辊加热过程中的瞬态温度场和奥氏体化进程,建立了加热奥氏体化过程的数学模型。通过采样轧辊内部一些特定位置的加热曲线验证了模拟结果的准确性,根据模拟结果提出了优化的冷轧辊加热工艺,该工艺明显地缩短了加热时间,具有显著节能的效果。     

Cr离子高温注入Al靶的传质模型

利用注入离子在固体中传输理论和辐照增强扩散理论建立了金属离子高温注入金属Al靶的传质模型,计算了金属离子高温注入的浓度-深度分布.在所建立的传质模型中采用动态Monte Carlo方法模拟离子注入过程,引入饱和浓度限模拟晶体靶局部饱和现象;采用基于辐照增强扩散的扩散方程描述注入粒子扩散过程;根据缺陷线性退火理论确定辐照增强扩散系数;结合杂质原子和非平衡空位扩散方程给出了注入粒子的浓度分布;在扩散方程中引入了空位源函数并考虑了离子溅射造成的表面退让效应.针对离子能量140keV,注入剂量2×10~(17)cm~(-2),温度250,400和510℃的Cr离子注入Al靶计算得到的浓度-深度分布与实验结果相符.     

Laser melt injection in aluminum alloys: on the role of the oxide skin

In this paper the method of laser melt injection of SiC particles into an aluminum substrate is investigated both experimentally and theoretically. An extremely small operational parameter window was found for successful injection processing. It is shown that the final injection depth of the particles is controlled mainly by the temperature of the melt pool rather than by the particle velocity. A theoretical model that takes into account the wetting behavior and the particle penetration processes is developed on the basis of the observed particle velocity, thickness and area fraction of oxide skin that partially covers the surface of the heated aluminum melt pool. The model reveals the role of the oxide skin: it is relatively strong at low temperature and acts as a severe barrier for the injection process. It was found that preheating the aluminum substrate results in a higher temperature of the melt pool and partial dissolution of the oxide skin, through which the injected particles are able to penetrate.     

Analytical model of the catchment efficiency in high speed laser cladding

Today laser cladding is a well known technique for the generation of functional layers and/or regeneration of parts. In comparison to alternative processes like thermal spraying and overlay welding laser cladding has some disadvantages. The processing time of laser cladding is comparably high and the catchment efficiency can be low. These facts can make the laser cladding process expensive. However it is possible to decrease the overall processing time and to increase simultaneously the efficiency for laser cladding.In this study a model is described which evaluates the catchment efficiency with respect to the melt pool geometry. The paper takes two effects into account. The primary effect is given by the particles diving directly into the melt pool. The secondary effect is given by the amount of powder particles molten in the laser beam during the time of flight and pointing at the surface beside the melt pool. A comparison between the experiment and the model shows a sound agreement.     

Mechanisms of grain refinement by intensive shearing of AZ91 alloy melt

It has been demonstrated recently that intensive melt shearing can be an effective approach to the grain refinement of both shape casting and continuous casting of Mg alloys. In the present study, the mechanisms of grain refinement by intensive melt shearing were investigated through a combination of both modelling and experimental approaches. The measurement of the cooling curves during solidification, quantification of grain size of the solidified samples, and image analysis of the MgO particle size and size distribution in the pressurized filtration samples were performed for the AZ91 alloy with and without intensive melt shearing. The experimental results were then used as input parameters for the free growth model to investigate the mechanisms of grain refinement by intensive melt shearing. The experimental results showed that, although intensive melt shearing does not change the nucleation starting temperature, it increases the nucleation finishing temperature, giving rise to a reduced nucleation undercooling. The theoretical modelling using the free growth model revealed quantitatively that intensive melt shearing can effectively disperse MgO particles densely populated in the oxide films into more individual particles in the alloy melt, resulting in an increase in the MgO particle density by three orders of magnitude and the density of active nucleating MgO particles by a factor of 20 compared with those of the non-sheared melt. Therefore, the grain refining effect of intensive melt shearing can be confidently attributed to the significantly increased refining efficiency of the naturally occurring MgO particles in the alloy melt as potent nucleation sites.     

Kinetic behaviour of TiB2 particles in Al melt and their effect on grain refinement of aluminium alloys

Solidification experiments were carried out to investigate the kinetic behaviour of TiB₂ particles in Al melt and their effect on the grain refinement of commercially-pure Al. A model was proposed to describe the kinetic behaviour of TiB₂ particles during the whole process from the addition of TiB₂ to the melt to the freezing of the melt. The results indicate that TiB₂ particles are not stable in Al melt. They may dissolve and coarsen during the holding period and grow during the cooling period of the melt. The kinetic behaviour of TiB₂ particles in the melt has a great influence on their number density and the grain refinement. Solute Ti addition can suppress the dissolution, Ostwald ripening and growth behaviours of TiB₂ particles.     

初生硅在熔体中的溶解动力学

研究了初生硅在熔体中的溶解特性，并以原子扩散为模型，考虑界面反应等因素的影响，建立了初生硅在过热熔体中的溶解动力学模型。同时以Al-17%Si合金为研究对象，采用等温液淬技术，对所建立的模型进行了实验验证。结果表明，初生硅在熔体中的溶解机制不是单纯受扩散控制的，而是由扩散、界面反应共同作用的结果，文中所建立的初生硅溶解模型可以较好地描述初生硅在不同温度过热熔体中的溶解特性。     

熔铸-原位合成TiC/7075Al复合材料的微观组织和凝固机制

采用熔铸-原位合成法制备了TiC/7075Al复合材料并对其微观组织和凝固机制进行了研究。原位合成复合材料中的TiC颗粒以近球形为主,平均尺寸小于700 nm。随着TiC颗粒含量的增加,复合材料的晶粒尺寸明显减小,当TiC颗粒含量为8wt%时,基体晶粒尺寸可以减小至10μm左右。熔体反应过程中,随着TiC增强相颗粒含量的增加,凝固前沿的流体的粘度增加,降低了TiC颗粒的临界裹入速度,同样在反应时降低温度将增加熔体的粘度,有利于TiC颗粒的裹入。     

Uniform distribution of TiCp in TiCp/Zn-Al composites prepared by XD^TM

The prefabricated Al/TiC alloy with high TiC particle content was prepared by XD^TM process,The uniform distribution process of TiC particles in the stationary zinc melt was studied and analyzed using self-made experimental equipment,and the model of the uniform distribution process was built.The results show that zinc diffuses into the prepared Al/TiC alloy after it is placed in the zinc melt at temperatures below the melting point of aluminum,which leads to the decrease of the liquidus temperature of Al-Zn alloy in the surface layer of Al/TiC alloy.When the liquidus temperature of Al-Zn alloy is equal to or below the temperature of zinc melt,Al-Zn alloy melts and TiC particles drop with it from the Al/TiC alloy and then transfer into the zinc melt and finally distribute uniformly in it.     

A new technology for the production of aluminum matrix composites by the plasma synthesis method

Aluminum matrix composites were produced via the plasma injection of reinforcing particulates into aluminum melts stirred electromagnetically. In this process, a metallic wire supplied to the active zone of plasma torch disintegrated into fine metallic particles. In the plasma arc, the particles are heated above the melting point and accelerated to close to sonic speed, which helps with the incorporation of the particles into the melt. In this study, the possibility of producing aluminum matrix composites reinforced by intermetallic compound particles via plasma synthesis is demonstrated.     

Ag-Ni电接触材料快速/亚快速凝固过程研究

采用快速/亚快速凝固方法制备了富Ni相粒子弥散分布于Ag基体的Ag-Ni合金。建立了Ag-Ni合金凝固过程中组织演变的动力学模型,模拟计算了Ag-Ni合金凝固组织形成过程,分析讨论了合金成分对Ag-Ni合金凝固组织形成过程的影响。结果表明,合金的Ni含量越高,凝固组织中富Ni相粒子平均尺寸越大;Ag-Ni合金熔体冷却凝固时,富Ni相液滴/粒子的尺寸主要受形核和长大控制,Ostwald粗化作用很弱。     

电磁搅拌铝合金熔体速度场计算及分析

为优化电磁搅拌工艺,用ANSYS软件对圆柱形铝合金熔体速度场进行了数值模拟.结果表明:在小于0.86倍熔体半径的范围内,熔体切向运动为强迫涡.涡核旋转角速度约为电磁场同步转速的1/26.涡核与坩埚壁间的熔体径向流层间具有较大的剪切速率,这对增强颗粒的润湿复合以及半固态组织的获得有利;而在涡核内,剪切速率接近于0,因此没有这种作用.采用环状熔体是解决该问题的办法之一.熔体纵切面内剪切速率的计算结果表明,剪切速率随半径增大而增大,而在高度方向上,则呈现中间大、上下两端小的特点.运动轨迹的计算说明,总体上,熔体质点呈螺旋式上升,但底部熔体流速低,且其运动范围基本上限于底部,易导致增强颗粒沉淀于底部,不利于其均匀分布.