超重力场对Al-17Si-4.5Cu熔体中固相夹杂分离的影响

将Al-17Si-4.5Cu熔体中初生Si颗粒模拟为固相夹杂物,利用超重力场恒温分离与受力分析、理论计算的方法研究熔体内部夹杂颗粒在不同重力场中的定向分离行为。结果表明,超重力场可以有效强化铝熔体中夹杂物的定向分离效果,且重力系数越大,Si颗粒分离效果越好。在普通重力场(G=1)条件下,直径为30μm的Si颗粒平衡运动速度为6.08×10-5 m/s,Si颗粒的分离效率仅为11.01%;而当超重力场G=500时,Si颗粒的运动速度为3.04×10-2 m/s,Si颗粒的分离效率达到了71.91%。     

超重力熔铸铁基金属陶瓷材料多相运动学特征及其致密化机制

采用Fe_3O_4/Al/铁基硬质合金的铝热体系,超重力熔铸铁基金属陶瓷梯度材料,分析了超重力场中多相(硬质合金颗粒、Al_2O_3陶瓷相及气体相)在高热高温铁熔体内的运动学特征及其致密化机制。结果表明,根据Stocks定律,弥散相在高温熔体内的运动速度影响因素主要有颗粒与基体熔体密度差、超重力系数、颗粒半径及温度等,在一定的超重力系数下,材料的致密度与气泡尺寸、铁熔体存在时间有关。V-Fe和Cr-Fe 2种颗粒主要集中于金属陶瓷材料的顶端,沿超重力方向粒子尺寸逐渐减小,而Mo-Fe颗粒主要集中在金属陶瓷材料与45钢分界面处,不同颗粒在材料内的分布状况有较大差异,这是金属陶瓷材料硬度呈梯度变化的主要原因。     

镁合金熔体净化工艺的研究

研究了镁合金再生过程中熔体内夹杂物含量、尺寸与静置时间的关系,以及主要合金成分和杂质元素含量的变化规律.应用Stokes公式模拟了夹杂物沉降距离与静置时间的关系,分析了影响夹杂物沉降速度的因素.结果表明:在镁合金废料完全熔解后静置5～10 min,可以将熔体内夹杂物的含量降至0.5%以下,夹杂颗粒尺寸小于0.3 mm.234熔剂的精炼效果好于RJ-1熔剂,经234熔剂精炼后静置8 min,镁合金熔体中的夹杂物含量降至0.02%以下,夹杂颗粒尺寸小于10μm.夹杂物沉降速度与夹杂半径的平方、夹杂密度成正比,与镁合金液粘性系数及镁合金液密度和夹杂密度的比值成反比.     

超重力场辅助燃烧合成钼铜功能梯度材料（英文）

采用超重力场辅助燃烧合成的方法制备了钼铜功能梯度材料。燃烧合成生成的Cu熔体在1000 g超重力场作用下渗透进入Mo粉坯中,随着熔体温度降低及渗透压力减小,沿超重力场方向上形成组分梯度分布的钼铜功能梯度材料。采用X射线衍射(XRD)、扫描电子显微镜(SEM)对样品沿超重力场方向的物相组成和微观形貌进行表征,利用激光闪射法、维氏硬度计对样品沿超重力场方向的热扩散系数的硬度值进行测试。结果表明:样品沿超重力场方向钼铜合金组分渐变,Mo含量由75 vol%减小至40 vol%,相对密度相应的由97.6%降低至96.5%。相对密度的降低可能是由沿超重力场方向Cu熔体冷却体积收缩增大造成的。钼铜功能梯度沿超重力场方向的热扩散系数由43.2 mm~2·s~(-1)增加至66.6 mm~2·s~(-1),硬度值由1390 MPa逐渐减小至710 MPa。     

钢液夹杂物粒径与上浮时间关系研究

基于单个球形夹杂物为研究对象,忽略夹杂物间及对流等因素的影响,对比计算了钢液中夹杂物的匀速及加速上浮时间,并分析了密度条件和夹杂物尺寸对上浮时间的影响。结果表明,上浮时间与匀速处理时相对误差较小,可以将夹杂物的上浮按照匀速过程处理;浇铸前钢液进行5~10 min镇静处理,可使钢液中密度为2 700~3 100 kg/m3的尺寸较大夹杂物(dФ50μm)完全上浮,有效避免铸钢件上表面或铸锭上部产生夹渣或夹杂类缺陷,减少轧材或轧板的表面缺陷。随夹杂物颗粒密度增大,其上浮时间将延长。而夹杂物尺寸的减小,上浮时间急剧上升,正比于1/r2。     

Ce、Cu合金化高强高效无取向硅钢中的夹杂物和析出相分析

设计并制备了含Cu和Ce的高强高效无取向硅钢。通过热力学计算、FactSage和JmatPro相图计算以及扫描电镜(SEM)、透射电镜(TEM)和能谱仪(EDS)等研究了不同Cu含量的含Ce无取向硅钢中夹杂物和析出相粒子性质。结果表明：Ce的添加降低了试验钢中富Cu析出相的开始析出温度。Cu含量不仅影响富Cu析出相的尺寸、数量而且影响其形态，如1.24%Cu含量的钢中富Cu析出相尺寸细小、呈球状，2.24%Cu含量的钢中富Cu析出相尺寸较大且出现短棒状形态。Ce的添加改变了AlN、Al₂O₃等夹杂物的形态和尺寸，使夹杂物变性，降低了夹杂物对试验钢磁性能的有害影响。     

72A盘条钢中的夹杂物以及索氏体化率对力学性能影响

通过金相观察统计以及夹杂物电解与能谱分析,对不同批号72A盘条产品索氏体化率以及夹杂物类型与尺寸进行研究.结果表明,72A盘条中的夹杂物主要为尺寸小于20μm的氧化物夹杂,较大颗粒的夹杂物对盘条抗拉强度无显著影响;大颗粒夹杂物含量百分比较高的盘条断面收缩率较低;而盘条索氏体化率低是影响其抗拉强度的原因.     

稀土Ce去除纯Al熔体中氧化夹杂的机理

研究纯铝熔体中的稀土Ce对氧化夹杂含量的影响及其反应机理.结果表明,稀土元素Ce与夹杂发生化学反应,形成2种密度较大的Ce-Al-O多元含氧化合物,沉到底部与熔体分离,达到去除夹杂、净化熔体的目的.     

利用旋转磁场去除铝熔体中的夹杂物颗粒

研究了旋转磁场去除液态铝合金熔体中夹杂物颗粒的效果.将铝硅过共晶合金凝固过程中析出的初生硅颗粒视为夹杂物颗粒.采用旋转磁场,研究了密度比周围铝熔体密度大的初生硅夹杂物颗粒在旋转磁场下的分布规律.利用光学显微镜和数码相机对凝固试样的宏观及微观组织进行观察.实验结果表明:旋转磁场可以有效去除液态铝合金熔体中的夹杂物颗粒,并且旋转磁场的除杂效果随着磁场频率的增大而显著增加.因此旋转磁场提供了一种高效的金属熔体净化的方法.     

内置式搅拌磁场对连铸空心铸坯内夹杂物分布影响

耦合求解了电磁场方程以及夹杂物守恒方程,考虑了夹杂物间的湍流碰撞以及斯托克斯碰撞,计算获得了拉速以及行波式电磁搅拌对结晶器内夹杂物分布的影响规律。结果表明,结晶器内夹杂物的运动规律与钢液的流动状态密切相关,拉速越大,钢液的浸入深度越深,则结晶器出口处夹杂物的数量越多,夹杂物的尺寸越小。施加行波式搅拌磁场可以使钢液流动加强,并减小钢液的浸入深度,有利于夹杂物的聚集长大上浮,结晶器内夹杂物的尺寸较大,但数量减少。因此,在连铸空心管坯内部施加搅拌磁场有利于去除钢中夹杂物,从而改善连铸空心管坯的质量。     

离心加速条件下金属液中粒子的相互作用

建立了金属液中第二相粒子在离心加速条件下的运动规律理论模型,并根据该理论模型分析了金属液中第二相粒子的相互作用规律。结果表明：在离心加速场中粒子一直处于加速状态,不会达到均速运动状态;粒子直径越大、密度越大,在同样时间内,粒子移动的距离越远;在传输过程中,不但有因尺寸不引起的粒子追逐现象,而且在因密度不同引起的追逐现象,该现象是引起粒子碰撞、聚集及尺寸大（或密度大）粒子偏聚到试样外侧的主要原因,径向上初始位置不同的两个粒子,其间距随时间延长逐渐增长。如果在径向一条直线上有多个同间距的粒子,离心移动一段时间后,虽然任意两相邻粒子的间距比开始态增大,但各相邻粒子间距在新的时刻仍是相等的。     

INTERACTION OF PARTICLES WITH A SOLIDIFIED INTERFACE DURING SOLIDIFICATION OF METAL MATRIX COMPOSITE REINFORCED WITH PARTICLES

ＩＮＴＥＲＡＣＴＩＯＮＯＦＰＡＲＴＩＣＬＥＳＷＩＴＨＡＳＯＬＩＤＩＦＩＥＤＩＮＴＥＲＦＡＣＥＤＵＲＩＮＧＳＯＬＩＤＩＦＩＣＡＴＩＯＮＯＦＭＥＴＡＬＭＡＴＲＩＸＣＯＭＰＯＳＩＴＥＲＥＩＮＦＯＲＣＥＤＷＩＴＨＰＡＲＴＩＣＬＥＳＣＨＵＳｈｕａｎｇｊｉｅ;Ｗ...     

利用Marangoni对流制备均质偏晶合金

利用温度场下第二相液滴的Ｍａｒａｎｇｏｎｉ运动，设计了一种在地球重力场下制备均质偏晶合金的“控制铸造”新技术。在这种技术中，偏晶合金凝固界面前沿的第二相液滴将在重力场下作Ｓｔｏｋｅｓ运动和在温度梯度场下作与重力方向相反的Ｍａｒａｎｇｏｂｎｉ运动。     

Preparation of electrolytic copper powders with high current efficiency enhanced by super gravity field and its mechanism

Super gravity field was employed to enhance electrolytic reaction for the preparation of copper powders. The morphology, microstructure and size of copper powders were characterized by scanning electron microscopy, X-ray diffractometry and laser particle analysis. The results indicated that current efficiencies of electrolytic copper powders under super gravity field increased by more than 20% compared with that under normal gravity condition. Cell voltage under super gravity field was also much lower. The size of copper powders decreased with the increase of gravity coefficient (G). The increase of current efficiency can be contributed to the disturbance of electrode/electrolyte interface and enhanced mass transfer of Cu2+ in super gravity field. Meanwhile, the huge gravity acceleration would promote the detachment of copper powders from electrode surface during electrolytic process, which can prevent the growth of copper powders.     

气体保护熔炼条件下Mg-Gd-Y-Zr合金的夹杂物

本文研究了气体保护条件下,常规熔铸的Mg-Gd-Y-Zr合金中夹杂物的形貌、分布及形成原因,并通过计算分析了夹杂物的沉降行为.结果表明,Mg-Gd-Y-Zr合金中有MgO或Y的氧化物为主的球状、簇状、不规则状、线状的复合夹杂物和含熔剂夹杂物,夹杂物的平均尺寸为12.7μm,平均体积分数为0.26%.夹杂物出现的频率随其尺寸增大而急剧减小,尺寸在20μm以下的夹杂物占夹杂物总体积接近85%,尺寸在45μm以下的夹杂物占96%.计算结果表明,夹杂物沉降速率与其尺寸和密度相关;夹杂物密度增大,可使镁合金中夹杂物的最大尺寸减小,计算得到的合金中最大夹杂物的尺寸与实验结果基本一致.     

A study on elimination of alumina particles in molten aluminum using direct electromagnetic force

From the viewpoint of energy reduction, the recovery of metal scrap and its recycling have been rising as an important global subject. However, it is difficult to remove deleterious impurities, which have detrimental effects on the mechanical properties. In particular, it is difficult to eliminate nonmetallic inclusions such as alumina(Al₂O₃) in aluminum alloys when they are subject to recycling. In this study, an experiment on the elimination of the impurities in the melt by imposing electromagnetic force to molten aluminum was conducted. The principle behind these electromagnetic methods is that as the electromagnetic force induced in metal scarcely acts on non-metallic inclusions due to low electric conductivity, the non-metallic inclusions are moved to the direction opposite the electromagnetic force and can be separated from the melt. The prediction based on the theoretical analyses was confirmed through the visualization of the polystyrene particle motion in an NaCl aqueous solution. We also proposed optimum electromagnetic conditions such as current density, magnetic field intensity and particle size for eliminating the inclusion particles continuously found through numerical analysis and experiments.     

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.     

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.     

相场法模拟热耦合强度对纯Ni枝晶生长的影响

基于Karma的薄界面极限相场模型,研究了相场和温度场耦合强度对过冷纯Ni熔体中枝晶生长行为的影响。模拟结果表明:随着热耦合强度的减弱,相场受温度场的影响作用减弱,固-液相界面前沿扰动变大,主枝出现二次枝晶并逐渐发达粗化,其粗化方式由缩颈熔断向枝晶臂合并方式转变。同时,枝晶尖端的生长速率增大、曲率半径减小。瞬态过程中枝晶尖端生长速度大于稳态生长速度,随着生长过程的进行,枝晶尖端生长速度逐渐降低,直至达到稳态值,计算结果与微观可解理论吻合良好。