稀土对铸造铝铜合金准固态和准液态区的影响

本文以ＺＬ２０１Ａ为研究对象，采用自行设计的实验装置研究了富Ｃｅ混合稀土，Ｌａ，Ｙ和Ｃｅ对合金准固态和准液态区的影响。研究表明，稀土能不同程度地降低准固相线温度，缩小了准固态区，扩大了准液态区。并提高合金固相线附近的强度，明显地增加合金准固态强度增长率，降低合金的热裂倾向性。     

铝硅合金凝固过程中的力学行为和热裂倾向性

利用自制的准固态力学性能测试装置,对铝硅合金的准固态力学性能进行了较为系统的测试,得出了反映不同含硅量铝硅合金的准固态力学行为参数(强度、断裂应变、准固态区间等),并分析了这些参数与热裂倾向性的关系。     

铝铜合金准固态力学行为和凝固过程应力应变及热裂纹数值模拟

作者研究了铝铜合金准固态力学行为和凝固过程应力应变及热裂纹形成规律,得到了以下主要结果:(1)阐述了准固态断裂应变和低强塑性区的物理本质和意义及准固态力学性能与热裂倾向性的关系;(2)确立了铝合金准固态建模方法,建立了Al-5．14%Cu合金准固态流变模型和力学本构方程;(3)模拟了有热节拘束端棒形件和应力框凝固过程应力、应变和热裂纹的形成规律。     

A1—Cu合金凝固过程中准固态力学性能及微量元素的影响

采用自制实验装置研究了A1—5％Cu合金在凝固过程中的准固态强度、强度增长率、断裂应变以及B,Ti,盐类细化剂和富Ce混合稀土对合金准固态力学性能的影响．研究结果表明,合金的准固态区即热脆性区,B,Ti和稀土都能降低合金准团相线温度,提高强度增长率和准固相线附近的强度,稀土的作用强于B和Ti．合金的中添加盐类细化剂后,合金准固态强度和断裂应变都比未加盐类细化剂的要低     

Al—Cu合金凝固过程中准固态力学性能及微量元素的影响

采用自制实验装置研究了Ａｌ－５％Ｃｕ合金在凝固过程中的准固态强度,强度增长率,断裂应变以及Ｂ,Ｔｉ,盐类细化剂和富Ｃｅ混合稀土对合金准固态力学性能的影响。研究结果表明,合金的准固态区即热脆性区,Ｂ,Ｔｉ和稀土都能降低合金准固相线温度,提高强度增长率和准固相线附近的强度。稀土的作用强于Ｂ和Ｔｉ,合金的中添加盐类细化剂后,合金准固态强度和断裂应变都比未加盐类细化剂的要低。     

铸造Al-5Cu合金准固态断裂行为的研究

采用SEM观察手段并结合EDX分析 ,在合金的准固态区 ,通过观察Al 5Cu Mn合金准固态拉伸和热裂应力测试试样的断口形貌 ,研究了Ti、Ce等合金元素及其交互作用对Al 5Cu Mn合金准固态断裂行为的影响及其影响机理。通过对试验合金准固态力学性能的测试和大量SEM断口的观察分析研究 ,结果表明 ,Al 5Cu Mn中添加Ti元素可明显提高合金抗热裂能力 ,主要是由于其良好的细化晶粒效果 ;适量Ce元素的加入 ,不仅可细化晶粒 ,而且其在晶间富集形成的化合物还可有效改善低熔点共晶反应在准固态区的力学行为 ,对减小热裂倾向非常有利 ;Ti和Ce的综合作用对合金抗热裂水平的提高比单一元素更有效 ;热裂的产生首先表现为枝晶枝臂的屈服 ,其后的扩展则表现为脆性断裂占优的穿晶、沿晶混合型特征     

工具钢超塑性固态焊焊接面断口特征区域分析

采用扫描电镜及俄歇微探针等检测手段,通过对40Cr/T10A、Cr12MoV钢超塑性固态焊接过程中焊接面断口的观察分析,认为超塑性固态焊接接头形成过程中焊接面各微区焊合状态是非均匀的,并呈现出不同的断口形貌特征;若按微观上断口形貌特征分类,整个断口可分为类原始界面区、准冶金结合区和冶金结合区3个特征区域;接头形成过程可描述为冶金结合区、准冶金结合区逐渐增大而类原始界面区逐渐减小的过程.     

环形钢坯液态压力成形过程的数值模拟

利用ProCAST软件对Q235B环形钢坯的液态压力成形过程进行数值模拟,探讨了环件凝固过程中的温度场变化,得到了环件凝固过程中不同时间的固相分数,分析了工艺参数对环件凝固过程的影响。结果发现,环坯在液态压力成形过程中,各个部分在凝固过程中存在温度差,金属液与模具接触区域温度下降最快,最后凝固区域位于环件中部。环件凝固时间受压力的影响最大。浇注温度升高,凝固时间变长。凝固时间随着模具温度的升高而延长。     

A1－4．87％Si合金准固态流变性能研究

用自行研制的合金准固流变性能测试装置实测了Ａｌ－４．８７％Ｓｉ合金准固态温度下的流变曲线，由此建立了该合金的流变物理模型和应力－应变本构方程。根据实验结果，计算了该合金的流变特性本数位。并对结果进行了讨论和分析。     

Al—4.87%Si合金准固态流变性能研究

用自行研制的合金准固流变性能测试装置实测了Ａｌ－４．８７％Ｓｉ合金准固态下的流变曲线，由此建立了该合金的流变物理模型和应力－应变本构方程。根据实验结果，计算了该合金的流变特性参数值，并对结果进行了讨论和分析。     

真空吸铸AZ61A镁合金的亚快速凝固行为研究

设计了真空吸铸急冷法制备镁合金小尺寸薄片铸件工艺装置,实现了镁合金AZ61A的亚快速凝固.研究分析了亚快速凝固条件下镁合金凝固态组织的特点及其亚快速凝固行为,并与常规凝固镁合金进行了比较分析.结果表明:亚快速凝固过程中,极快的冷却速率使得熔体凝固过程中固/液界面推移的速率很快、局部凝固时间很短,抑制了溶质元素扩散,使其很大程度上固溶于基体组织中;镁合金的晶粒尺寸较常规凝固试样有了明显细化,晶粒度只有几个微米,且随着冷却速率的增加,其尺寸不断减小;提高了铸件成分及组织的均匀性,凝固态组织中析出的3-Mg17Al12相极少甚至消失,最终形成以过饱和c-Mg固溶体为主相的亚快速凝固组织.     

瞬时液相异种连接FSX-414/MBF80/IN738体系的固/液界面位置的预测(英文)

采用有限元差分法模拟FSX-414/MBF80/IN738体系异种瞬时液相(TLP)连接的等温凝固过程。将TLP连接模型分为2部分,并运用一个移动的液/固界面模型来研究他们。使用扩散方程对每部分接头进行预测,直到等温凝固过程结束;分别预测了这2部分的等温凝固完成时间、浓度分布曲线和固/液界面位置,认为这2部分固/液界面的交点是等温凝固的终点。为了获得一些必要的扩散数据,在不同温度、时间和真空条件下进行FSX-414/MBF80/IN738体系的瞬时液相连接实验。结果表明,实验结果与预测结果一致。     

A mathematical model of unidirectional solidification in cooled mold

For the unidirectional solidification in a mold cooled by air or water, several mathematical models have been proposed. However, some are complex series solutions, and some are good approximations only when solidification time is sufficiently small. Therefore, our research team proposes the present mathematical model, which is a good approximation when solidification time is sufficiently large. In order to estimate the convergency characteristics of the present model, numerical solutions were calculated with mold/solid heat transfer coefficients, which are experimentally determined by a previous and the present model.     

瞬间液相扩散焊过程中的接触熔化与等温凝固模型

接触熔化与等温凝固是瞬间液相扩散焊过程中两个非常重要的阶段,是获得优质连接接头的关键,一直以来也是学术界研究的热点.综述了接触熔化与等温凝固过程的动力学模型,包括接触熔化与等温凝固时间的解析解,接触熔化过程中反应层厚度与连接时间符合扩散控制的抛物线规则,以及等温凝固过程中液/固界面迁移的速度方程.并对现有模型进行了分析和讨论.     

SOLIDIFICATION MECHANISM OF UNDERCOOLED SINGLE PHASE ALLOYS

1.IntroductionInthesolidificationofundercooledalloymelts,thehighdrivingforceforcrystallization,i.e.,thefreeenergydifferencebetweenliquidandsolid,makesthecrystalsgrowrapidly(orrecalesce).Withthelatentheatreleasing,temperatureofthesystemquicklyrises.Hencetherapidsolidificationofundercooledmeltsoccursduringthetemperatureincrease,inwhichthethermodynamicandkineticconditionsofthesystemareinviolentchange.Forthiskindofsolidification,however,some.esea.ch...[1'2]stillanalyzeditinequilibriumdiagram,andar…     

静磁场对2024铝合金凝固组织的影响

通过热模拟试验及扫描电镜分析,研究了静磁场对2024铝合金显微晶粒度、凝固速度、合金元素分布的影响.结果表明,随着磁感应强度的增大,合金凝固组织明显细化,凝固时间变短,这与凝固前沿熔体内的塞贝克效应有关,使得熔体对流效应强于静磁场的制动效应;应用静磁场能够增强溶质原子在铝中的扩散,有利于提高合金元素的固溶度,减轻凝固组织的宏观偏析.     

The Effect of Undercooling on Solidification of YSZ Splats

We consider the rapid solidification of a molten YSZ particle, by solving the so-called hyperbolic equations for heat and mass transfer. The hyperbolic model predicts the interface undercooling (due to thermal and solutal effects) and velocity as a function of time, as well as the yttria redistribution within the solid phase. Results are then compared to corresponding ones that we obtained from a parabolic model, to assess the extent to which YSZ solidification is influenced by nonequilibrium effects. Results indicate that these effects are limited to the early part of the solidification process when undercooling is most significant. At this stage, the interface velocity is unsteady, and solute redistribution is most evident. As solidification decelerates, the nonequilibrium effects wane and solidification can then be properly modeled as an equilibrium process.     

Density and solidification feeding model of vacuum counter-pressure cast aluminum alloy under grade-pressuring conditions

The density of vacuum counter-pressure cast aluminum alloy samples under grade-pressuring condition was studied. The effect of grade pressure difference and time on the density of aluminum alloys was discussed, and the solidification feeding model under grade-pressuring condition was established. The results indicate the grade-pressured solidification feeding ability of vacuum counter-pressure casting mainly depends on grade pressure difference and time. With the increase of grade pressure difference, the density of all the aluminum alloy samples increases, and the trend of change in density from the pouring gate to the top location is first decreasing gradually and then increasing. In addition, in obtaining the maximum density, the optimal grade-pressuring time is different for samples with different wall thicknesses, and the solidification time when the solid volume fraction of aluminum alloy reaches about 0.65 appears to be the optimal beginning time for gradepressuring.     

连铸板坯凝固过程中夹杂物运动模拟研究

基于CFD建立了连铸过程中钢液流动、凝固及夹杂物运动三维数学模型。考虑铸坯弧形和水口形状,研究了连铸板坯凝固坯壳对钢液流动和夹杂物运动的影响,得出了夹杂物的上浮率及在凝固铸坯上的分布。研究结果表明,铸坯凝固对钢液流场有显著影响。凝固坯壳阻碍钢液向下流动,考虑凝固的钢液回流区更靠近弯月面,钢液流出回流区更趋于向铸坯中心运动;凝固的夹杂物上浮率相对于不考虑凝固的夹杂物上浮率高。     

Solidification with a quasiequilibrium two-phase zone

A set of nonlinear equations describing solidification with a two-phase zone (mushy region) is analytically solved in a general form in the case of quasi-steady-state crystallization of binary melts. Concentration, temperature distributions and the bulk fraction of the solid phase as functions of a spatial coordinate and physical and operating parameters of solidification are found within the mushy zone. The mushy region thickness and algebraic equation for the bulk fraction of the solid at the boundary solid phase–mushy zone are determined for the first time in a general form. A theory under consideration strengthens a hypothesis about a self-similar structure of the two-phase zone.