SiCp/A356复合材料半固态流变特性的研究

用自制的同轴圆筒旋转流变仪对SiCp/A356颗粒增强复合材料浆料的流变特性进行研究.结果表明,SiCp/A356复合材料在液态和半固态条件下,表现出非牛顿流体的特性,浆料稳态表观粘度随着剪切速率的增大而下降.当剪切速率达到一定值时,其剪切变稀特性减弱,显示出牛顿流体的特性.在连续冷却条件下,半固态浆料的表观粘度随着温度的降低而先缓慢后迅速增大.在总固相率相同时,SiCp/A356复合材料的表观粘度比A356合金低,加入的SiCp,体积含量越多,浆料流变性能越好.同时,在加入相同体积分数的SiC颗粒条件下,增强颗粒尺寸越小,浆料表观粘度越大.     

行波磁场作用对凝固过程中气泡的影响

研究行波磁场对铝合金除气行为的影响,计算行波磁场对气泡形核临界半径的影响。结果表明：在行波磁场作用下,气泡的临界形核半径随着电磁场强度的增大呈线性递减,电磁力促进了气泡的非均匀形核,电磁力使得气泡在熔体中长大,并在电磁力的驱动下向熔体的外部溢出。试样中的气泡数随行波磁场感应强度的增大而减少。     

云母微粒对聚丙烯流变性能及热性能的影响（英文）

采用毛细管流变仪测试云母微粒/聚丙烯(PP)共混熔体的流变性能,用热重分析仪研究云母微粒对PP热稳定性能的影响。结果表明:云母微粒/PP共混熔体属于非牛顿假塑性流体,其表规粘度随剪切速率的增大而减小;随着云母微粒含量的增加,熔体的流动性能基本呈下降趋势,但当云母质量分数为4%时,熔体的粘度接近于纯PP:温度升高使得熔体表观粘度降低,非牛顿指数增加:在相同剪切速率下,云母含量的增加对其混熔体粘流活化能的影响不大;添加云母微粒后可以显著提高PP的热稳定性能。     

TiB2／Al复合材料熔体的表观粘度

采用旋转柱体法研究了TiB2颗粒增强铝基复合材料熔体的表观粘度随温度的变化.结果表明,由于温度升高和转子的搅拌,陶瓷颗粒的分布变得均匀,熔体粘度在750～780 ℃时产生第一次不连续变化;之后颗粒沉降开始,熔体粘度在780～830 ℃温度段内开始逐渐增大.     

机械振动辅助激光熔覆NiCrBSi-TiC复合涂层中颗粒相行为特征

采用XRD,SEM和EDS分析了机械振动辅助激光熔覆NiCrBSi-TiC颗粒增强复合涂层中外加TiC颗粒和内生M₂₃C₆碳化物的生长形态、形成机制及其在γ-Ni固溶体间的分布特征.结果表明,熔池内大部分外加TiC颗粒在熔覆过程中溶解,溶解于镍基合金熔体中的过饱和Ti和C原子在冷却过程中又形成TiC颗粒,并以共晶方式析出,其通过M₂₃C₆型碳化物为核心异质形核,并侧向生长;同时,出现以TiC为心部,以（Ti,Cr,Ni,Fe,Si）C为外围包覆结构的复式碳化物.在振动作用下,底部粗大枝晶状共晶组织消失,振动引起的流体平流层使底部TiC颗粒上浮趋势减缓,出现双颗粒和花瓣状多颗粒TiC粒子簇.振动作用使熔覆层区域内的组织得到细化,枝晶间网状（Fe,Ni）固溶体中Cr含量升高,TiC颗粒析出增多,颗粒尺寸增加,平均粒径增加超过25%.从XRD谱可观察到,振动作用使涂层内主要硬质相的衍射峰增强,半高宽变宽,表明硬质相的晶格完整性提高,晶粒细化.振动作用促使颗粒相均匀弥散分布于基体枝晶内和枝晶间.     

半固态SCN-5H2O模型合金流变性与组织特征的耦合分析研究

采用旋转流变仪研究了剪切速率和不同工艺(连续冷却和重熔加热)对半固态SCN-5H2O(摩尔分数,％)透明模型合金流变性与微观组织的耦合影响规律.结果表明,剪切速率的跃变升高会导致合金熔体的表观黏度呈现出暂态的剪切稠化和稳态剪切稀化现象.而随着剪切速率的增加,相应的组织呈现出非枝晶颗粒尺度逐渐减小,团聚体的分布更加分散的...     

6061合金外熔体温度对7075半固态合金固相颗粒定向生长的影响

利用固/液复合铸造技术,将液态6061合金熔体包覆7075合金半固态坯料,制备出包覆型7075/6061双金属复合铸锭。研究了外熔体温度对包覆型7075/6061双金属复合铸锭半固态颗粒生长形态的影响。结果表明:在固/液复合铸造工艺条件下,受到6061合金外熔体温度的影响,内层7075合金半固态固相颗粒沿平行于复合铸锭轴向方向发生了定向生长;随着外熔体温度的升高,内层半固态固相颗粒定向生长速率显著增大;而靠近复合界面处的半固态固相颗粒定向生长速率远大于复合铸锭心部的半固态固相颗粒定向生长速率;外熔体温度越高,半固态显微组织的晶界激活能或表观激活能越低,越有利于半固态固相颗粒发生定向生长。     

冷却条件对超声振动法制备AZ91半固态浆料组织的影响(英文)

利用超声振动法制备AZ91合金半固态浆料,在不同温度区间和冷却速率下对熔体进行超声处理,研究冷却条件对AZ91半固态浆料微观组织的影响。结果表明:在形核阶段,熔体在超声振动引发的空化和声流效应作用下,能够获得细小、近球状的初生α-Mg固相颗粒;在固液相线温度区间内,随着超声温度下限的降低,半固态浆料的固相率和固相颗粒的平均尺寸增加;在超声振动过程中,随着冷却速率的提高,半固态浆料的固相率增大,固相颗粒的平均形状因子降低。在本实验条件下,适宜的超声振动温度区间为605°C到595°C或590°C,合适的冷却速率为2~3°C/min。     

Cu-13.5%Sn合金雾化液滴凝固过程模拟

在群体动力学的基础上,提出了描述Cu-13.5%Sn（质量分数）合金雾化液滴凝固过程的动力学模型;并将其与液滴的传热方程和运动方程相耦合,对雾化液滴的冷却凝固过程进行了模拟分析,探讨了液滴尺寸、气体初始速度、熔体过热度和初生相与异质形核基底间润湿角对液滴凝固行为的影响.模拟结果表明：本模型能够很好地描述雾化液滴的凝固过程;液滴冷却至一定温度开始形核,随后晶粒长大;液滴直径越小,冷却速度越快,液滴内晶粒数量密度就越高,凝固结束时晶粒亦越细小.形核润湿角和熔体过热度的增加,导致液滴内晶粒数量密度降低,晶粒半径增大;而气体初始速度的增加,有利于液滴内晶粒细化.     

紫铜棒材轴向加压精密塑性剪切变形区的金相组织和断面特征

研究了轴向压力作用下紫铜棒料塑性剪切分离面附近的微观组织形态、剪应变和硬度分布以及剪切分离面形貌.结果表明:剪切分离面变形区可分为3个区域,在距表面100～250μm薄层内,晶粒发生了极其剧烈的大剪切塑性变形,其维氏显微硬度增大50%;剪应变随与剪切分离面距离的增大而减小;剪切分离面上断面呈月牙状,轴向压力增大,断面减小;断面上有大量长条形微孔洞,是由微孔形核后在剪应力作用下沿剪切方向长大和聚合而形成的.     

超声及电磁场对铝合金熔体影响的数值模拟及试验研究

针对铝合金熔体的超声及电磁搅拌处理过程,创建了超声场、电磁场、流场和温度场的数学模型,并采用COMSOL Multiphysics软件求解模型,得到了超声场、电磁场和超声/电磁复合场对铝合金熔体内流场和温度场的分布规律,并通过试验对模拟结果进行了验证。结果表明,增加超声功率使得声压幅值和流场的流动速率均随之增加,同时会使熔体的温度梯度逐渐减小;施加电磁场后产生的电磁搅拌改变了熔体的流动方向且使熔体的流动速率显著增大,这对熔体的温度分布产生了较大影响;在超声和电磁复合场下,电磁场比超声场对熔体流场和温度场的影响更大,且占主导地位。数值模拟结果和试验结果符合较好。     

外加横向磁场对304不锈钢焊接熔池影响机理分析

为了改善焊缝成形及提高焊接零件组织和性能,文中采用有限元法对外加磁场作用下的304不锈钢焊接熔池进行电磁场和热流场之间的耦合分析,得到了有无外加横向磁场作用下熔池内液态金属流动的速度矢量分布. 结果表明,外加磁场使熔池横截面最大流速分布由单一的熔池中心中部改为熔池中心上表面略靠下和熔池底部;熔池纵截面最大流速由首尾端漩涡交汇处改为沿两个漩涡流动方向较均匀分布,这是由于电磁压力抵消了部分表面张力,使表面张力的作用位置更靠近熔池中心位置. 在304不锈钢上进行堆焊试验,焊道横截面组织形貌证实了上述模拟结果.     

Numerical simulation on electromagnetic field,flow field and temperature field in semisolid slurry preparation by A-EMS

A two-dimensional computational model coupling an annular electromagnetic stirring (A-EMS) with a macroscopic heat and fluid flow analysis in Al-alloys semisolid slurry preparation was developed. The dynamic evolutions of the electromagnetic field, flow field, and temperature field were presented successfully by commercial software ANSYS 10.0 with corresponding experimental verification. A horizontally rotational electromagnetic field and, thereby, a more intensive velocity field were uniformly distributed in the stirred melt even at commercial frequency, and thus, a lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained compared with the normal electromagnetic stirring. The simulation results were in good agreement with experimental ones.     

Study on in-situ WC particles/tungsten wire reinforced iron matrix composites under electromagnetic field

By applying electromagnetic field to a system consisting of tungsten wires and grey cast iron melt, the grey cast iron matrix composite reinforced by either in-situ WC particles or the combination of in-situ WC particles and the residual tungsten wire was obtained. By means of differential thermal analysis (DTA), the pouring temperature of iron melt was determined at 1,573 K. The microstructures of the composites were analyzed by using of X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with an energy dispersive spectrum (EDS) and pin-on-disc abrasive wear test. The obtained results indicated that, with the enhancing frequency of electromagnetic field, the amount of in-situ WC particles gradually increases, leading to continuous decrease of the residual tungsten wires. When the electromagnetic field frequency was up to 4 kHz, tungsten wires reacted completely with carbon atoms in grey cast iron melt, forming WC particals. The electromagnetic field appeared to accelerate the elemental diffusion in the melt, to help relatively quick formation of a series of small Fe- W-C ternary zones and to improve the kinetic condition of in-situ WC fabrication. As compared with the composite prepared without the electromagnetic field, the composite fabricated at 4 kHz presented good wear resistance.     

立式离心场下钛合金熔体充填及凝固过程研究

研究立式离心场下不同铸造工艺参数对钛合金熔体的充填及凝固缺陷形成的影响。结果显示,立式离心场下得到的钛合金铸件质量优于重力场下的铸件。立式离心场下,合金熔体由于受离心力和科氏力的作用,沿着与旋转方向相对的型壁进行充填,且熔体的截面面积随充填长度的增加而逐渐减小,但是在内浇口处由于速度降低导致截面面积有所回升。此外,铸型的旋转方向,旋转半径及旋转速度直接影响铸件缺陷的形成。旋转方向直接影响合金熔体的充填顺序,进而影响合金熔体的凝固顺序及缺陷位置。实验结果显示,旋转半径及旋转速度的增加有利于减少铸件的缺陷体积。     

SiCP增强泡沫铝基复合材料的制备工艺研究

将SiC颗粒增强铝基复合材料的制备技术与泡沫铝熔体发泡技术相结合,探索了制备SiC颗粒增强泡沫铝基复合材料的工艺方法。讨论了SiC颗粒与铝基体之间存在的润湿性,界面反应以及SiC颗粒在熔体中沉降等问题,通过选择合适的合金成分,对SiC颗粒进行预处理,采用特定的搅拌和发泡等一系列工艺方案成功地予以解决。在熔体发泡过程中,通过严格控制发泡温度、搅拌速度和搅拌时间等工艺参数,制得了孔隙率基本可调,SiC颗粒和孔洞分布均匀的泡沫铝样品。     

磁场作用下Al-Pb偏晶合金的凝固过程

在恒定磁场作用下对Al-Pb合金进行定向凝固实验, 考察了合金成分、凝固速度、恒定磁场对凝固组织的影响. 模拟研究了恒定磁场作用下Al-Pb合金定向凝固组织的形成过程, 分析了磁场的影响机理和合金成分、凝固速度、磁场强度对弥散型凝固组织获得的影响. 模拟和实验均表明恒定磁场促进弥散型偏晶合金凝固组织的形成.     

Application of a time-dependent constitutive model to rheocast systems

A mathematical model has been developed to describe the velocity field in an agitated Al- 5Cu alloy in which B4C particles were suspended at different loading rates of up to 40 %. The material system was agitated by means of an electromagnetic rotary stirrer. The non- Newtonian behavior of the melt/solid slurry was allowed for using two models: the steady- state model of Joly and Flemings and the model of Brown, which takes account of time- dependent behavior. Calculations have shown that the two models behave similarly at high shear rates. In addition, if agitation was discontinued, very little time was required for the velocity (and hence the fluidity) of the slurry to decay.     

Wear properties of rheo-squeeze cast aluminum matrix reinforced with nano particulates

There are many approaches to fabricate nanoparticles reinforced aluminum matrix composites. However, uniform distribution of nanoparticle within aluminum matrix remains a difficult challenge. In this study, a novel method is used by taking the advantages from squeeze casting of semi-solid aluminum slurry combined with electromagnetic field to refine the microstructure of the primary Al and eutectic Si phase, plus to obtain uniform distribution nano alumina particles in the aluminum matrix. It is noted that electromagnetic field plays an important role in the formation of non-dendritic primary α-Al particles and a great microstructure refinement occurs as a consequence of the pressure application. It can be seen that the increase in electromagnetic field causes smaller and rounder primary α-Al particles. A comparative study on abrasive wear behavior of nano Al₂O₃ reinforced aluminum metal matrix composite has been carried out in the present investigation. The mass loss of the pin was used to study the effect of Al₂O₃ addition on the wear resistance of the composite materials.     

电磁搅拌制备TiB_2颗粒增强7055铝基复合材料的研究

在电磁搅拌的条件下,通过盐-熔体原位反应生成了亚微米级TiB_2增强颗粒,并在熔体凝固过程中施加电磁搅拌,获得TiB_2颗粒增强的7055基复合材料铸态组织.试验结果表明,电磁搅拌作用下,熔体的传热和传质速度增加,铝液与反应盐的接触面积也增大,TiB_2颗粒的生成量大大提高,并促进了颗粒在基体中的弥散分布,减少了颗粒的团聚;同时,在熔体凝固过程中施加电磁搅拌,提高了基体材料的致密度,细化了基体晶粒尺寸.