电磁场对铝合金铸造组织和性能的影响

铝硅合金的机械性能与其微观结构密切相关,为了改良合金的微观组织,提高材料性能,人们尝试利用各种手段控制铝合金的凝固过程。通过研究和生产实践发现,在金属的凝固过程中施加电磁场可以改善材料的组织性能并优化工艺过程。由于电磁场在金属凝固过程中会产生多种物理效应,因此,探讨电磁场对改善合金微观组织的作用,找出较优的工艺参数,对改善材料的组织性能,提高产品质量具有重要意义。     

共晶合金凝固组织数值模拟的研究进展

论述了共晶合金凝固组织数值模拟的主要方法和研究进展。指出以合金的化学成分及冷却过程的工艺参数为条件，模拟其凝固组织的形成过程，将成为共晶合金凝固过程微观模拟的新的发展方向。     

二元合金凝固微观模型的研究现状

基于对二元合金凝固过程宏观传输耦合数学模型中非平衡凝固路径和局部液相溶质浓度的确定,详细讨论了两种不同类型的微观凝固数学模型,即凝固动力学模型和凝固微观偏析模型,对其中的确定性凝固动力学模型和微观偏析半解析模型的研究现状分别进行了回顾,分别讨论了凝固动力学模型和微观偏析模型的主要影响因素,即过冷度和形核率以及固相反向扩散和枝晶结构粗化,对凝固微观模型在合金凝固过程耦合数值模拟中的应用价值及其未来的研究方向进行了阐述.     

定向凝固Fe81Ga19合金的组织和磁致伸缩性能

利用区熔定向凝固技术制备Fe81Ga19合金棒,研究不同的定向凝固速度下,Fe81Ga19合金的微观组织、择优取向和磁致伸缩性能.研究发现:随着凝固速率的下降,试样沿轴向生长成柱状晶,晶界数目减少,取向发生改变.凝固速度为10μm/s的Fe81Ga19合金的组织由尺寸较大的柱状晶组成.当凝固速度υ=30μm/s时,试样...     

Nd-Fe-B 包晶合金的定向凝固组织及相选择

对 Nd11.76Fe82.3B5.88包晶成分和 Nd13.5Fe79.75B6.75过包晶成分合金进行了高梯度定向凝固和激光快速定向凝固实验,研究了 Nd-Fe-B 合金组织形成及相选择与凝固参量(温度梯度 G,生长速度 V,合金成分 C0)之间的对应关系.针对包晶相为无固溶度的化学计量比结构的 Nd-Fe-B 合金体系,讨论计算了合金定向凝固过程γ-Fe及包晶T1相的界面温度随生长速率的变化,获得了 Nd-Fe-B 合金定向凝固相/组织选择图,确定了合金凝固中各相及生长形态转化的条件.Bridgman定向凝固实验中,随着抽拉速率的增加,T1相由平面/小平面向枝晶形貌转变;Nd13.5Fe79.75B6 75合金的激光实验中,凝固速率由4.4～5.0 mm/s时,领先析出的组织由γ-Fe 枝晶转变为 T1 相枝晶.实验结果与理论计算给出的相/组织选择图吻合较好.     

Nd-Fe-B包晶合金的定向凝固组织及相选择

对Nd11.76Fe82.36B5.88包晶成分和Nd13.5Fe79.75B6.75过包晶成分合金进行了高梯度定向凝固和激光快速定向凝固实验,研究了Nd-Fe-B合金组织形成及相选择与凝固参量(温度梯度G,生长速度V,合金成分C0)之间的对应关系.针对包晶相为无固溶度的化学计量比结构的Nd-Fe-B合金体系,讨论计算了合金定向凝固过程γ-Fe及包晶T1相的界面温度随生长速率的变化,获得了Nd-Fe-B合金定向凝固相/组织选择图,确定了合金凝固中各相及生长形态转化的条件.Bridgman定向凝固实验中,随着抽拉速率的增加,T1相由平面/小平面向枝晶形貌转变;Nd13.5Fe79.75B6.75合金的激光实验中,凝固速率由4.4~5.0mm/s时,领先析出的组织由γ-Fe枝晶转变为T1相枝晶.实验结果与理论计算给出的相/组织选择图吻合较好.     

热处理和冷变形对连续定向凝固Cu-Ag合金性能的影响

研究了连续定向凝固Cu-Ag合金铸态试样及其经过大变形冷加工后线材的微观组织和性能,分析了热处理和冷变形对连续定向凝固合金的强度和电导率的影响.经过大变形冷加工后,Cu-Ag合金具有致密的纤维组织结构,强度进一步增加,电导率略有下降.在低温热处理后,Cu-Ag合金强度增加,电导率得到恢复.高温热处理时,Cu-Ag合金强度和电导率都下降.     

易切削钢9SMn28凝固过程的CAFE法模拟

为了耦合缩孔和疏松模拟凝固过程三维微观组织,对元胞自动机--有限元(CAFE)法的物理本质和数值计算方法进行了分析,采用CAFE法对易切削钢9SMn28铸件进行了凝固过程、缩孔和疏松及三维微观组织的模拟.模拟结果表明:在空冷条件下,铸件表层的凝固是在连续降温过程中进行的,内部是先等温凝固,后降温凝固;缩孔和疏松模拟结果与实际铸件的基本相符;实现了9SMn28合金三维微观组织的模拟,模拟结果与实验吻合较好.     

柱塞激光熔覆镍基合金工艺与组织结构分析

本工作针对高压匀质机柱塞应用背景,在奥氏体不锈钢为基材的柱塞上激光熔覆镍基硬面合金,对其工艺、微观组织结构和性能进行了较深入的分析研究．通过扫描电镜、Ｘ光衍射、金相等微观分析方法,对快速凝固激光熔覆合金层的非平衡态微观组织特性与其性能关系进行研究．结果表明：在激光熔覆柱塞表面获得了镍基硬面合金层与不锈钢基材的优良冶金结合;合金层微观组织为超细的共晶组织,在含Ｃｒ、Ｓｉ、Ｃ、Ｂ元素的过饱和γＮｉ（Ｆｅ）奥氏体基体中,均匀分布着细密的树枝状碳化物、硼化物及硅化物;这是它具有良好的力学性能和耐磨耐蚀使用性能的关键．还对热喷涂柱塞进行了微观组织结构和性能的对比分析     

旋转造粒制备Al-Pb合金颗粒

研究了用旋转造粒法制备Al-8Pb-3Si-2Sn-Cu合金颗粒的宏观特征与微观组织.研究结果表明Al-Pb合金颗粒的形状受合金熔体表面张力的影响,呈近球形,颗粒直径随熔体旋转速度的提高而减小;当颗粒直径小于3.9 mm时,合金的非平衡凝固可以克服Pb重力偏析,随颗粒直径的减小,合金凝固过程从非平衡过偏晶状态转变为非平衡亚偏晶状态,在微观上Pb分布更加均匀.     

包晶凝固的研究现状及进展

目前人们对包晶凝固过程和机理的研究远没有单相和共晶体系那样深入,长期以来仅限于定性的描述,至今还没有形成较为完整的理论体系,也没有单相和共晶合金那样较成熟的凝固模型。本文评述了其近年来包晶凝固的理论、各种假设模型,讨论了定向凝固过程中组织,生长机制等。     

Thermodynamic properties and microstructural characteristics of binary Ag-Sn alloys

The liquidus and solidus temperatures and enthalpy of fusion for Ag-Sn alloys are systematically measured within the whole composition range by differential scanning calorimetry (DSC). The measured enthalpy of fusion is related to Sn content by polynomial functions, which exhibit one maximum value at 52 wt%Sn and two minimum values around 21 wt%Sn and 96.5 wt%Sn, respectively. The liquidus slope, the solidification temperature interval, the solute partition coefficient and the entropy of fusion are calculated on the basis of the measured results. The undercoolability of those liquid Ag-Sn alloys solidifying with primary (Ag) solid solution phase is stronger than the other alloys with the preferential nucleation of ζ and ε intermetallic compounds. Morphological observations reveal that peritectic reactions can rarely be completed, and the peritectic microstructures are always composed of both primary and peritectic phases.     

Cu基亚稳难混溶合金液-液相变

通过气体雾化技术研究了Cu100-XFeX (X=15, 20, 30和40)合金的凝固行为. 考虑少量相液滴形核、扩散长大、空间迁移、凝固界面与液滴间的相互作用以及体积分数等共同影响因素,建立了能描述该类合金凝固组织演变动力学模型. 将数学模型与雾化液滴飞行过程中运动、传热和传质的控制方程相耦合,给出了数值求解方法,模拟计算了Cu基亚稳难混溶合金液-液相分离过程. 结果表明:富Fe粒子的平均尺寸随着Fe含量的增加而增大;少量相液滴形核发生在基体熔体过饱和度峰值附近;随着冷却速度的增大,雾化液滴中少量相液滴的形核率增大,但平均半径减小;少量相液滴在Marangoni迁移和与固/液界面相互排斥共同作用下,向雾化液滴中心迁移,使雾化粉末最终形成壳型组织结构.     

Solidification microstructure formation in HK40 and HH40 alloys

The microstructure formation processes in HK40 and HH40 alloys were investigated through JmatPro calculations and quenching performed during directional solidification. The phase transition routes of HK40 and HH40 alloys were determined as L → L + γ → L + γ + M₇C₃ → γ + M₇C₃ → γ + M₇C₃ + M₂₃C₆→ γ + M₂₃C₆ and L → L + δ → L + δ + γ→ L + δ + γ + M₂₃C₆ δ + γ + M₂₃C₆, respectively. The solidification mode was determined to be the austenitic mode (A mode) in HK40 alloy and the ferritic–austenitic solidification mode (FA mode) in HH40 alloy. In HK40 alloy, eutectic carbides directly precipitate in a liquid and coarsen during cooling. The primary γ dendrites grow at the 60° angle to each other. On the other hand, in HH40 alloy, residual δ forms because of the incomplete transformation from δ to γ. Cr₂₃C₆ carbide is produced in solid delta ferrite δ but not directly in liquid HH40 alloy. Because of carbide formation in the solid phase and no rapid growth of the dendrite in a non-preferential direction, HH40 alloy is more resistant to cast defect formation than HK40 alloy.     

Solidification,microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents

The influence of praseodymium(Pr) content on the solidification characteristics, microstructure, and mechanical properties of ZRE1 magnesium(Mg) cast alloy was investigated. The obtained solidification parameters showed that Pr strongly affected the solidification time, leading to refinement of the microstructure of the alloys. When the freezing time was reduced to approximately 52 s, the grain size decreased by 12%. Mg_(12)Zn(Ce,Pr) was formed as a new phase upon the addition of Pr and was detected via X-ray diffraction analysis. The addition of Pr led to a substantial improvement in mechanical properties, which was attributed to the formation of intermetallic compounds; the ultimate tensile strength and yield strength increased by approximately 10% and 13%, respectively. Pr addition also refined the microstructure, and the hardness was recovered. The results herein demonstrate that the mechanical properties of Mg alloys are strongly influenced by their microstructure characteristics, including the grain size, volume fraction, and distribution of intermetallic phases.     

Solidification,microstructure, and mechanical properties of the as-cast ZRE1 magnesium alloy with different praseodymium contents

The influence of praseodymium (Pr) content on the solidification characteristics, microstructure, and mechanical properties of ZRE1 magnesium (Mg) cast alloy was investigated. The obtained solidification parameters showed that Pr strongly affected the solidification time, leading to refinement of the microstructure of the alloys. When the freezing time was reduced to approximately 52 s, the grain size decreased by 12%. Mg₁₂Zn (Ce,Pr) was formed as a new phase upon the addition of Pr and was detected via X-ray diffraction analysis. The addition of Pr led to a substantial improvement in mechanical properties, which was attributed to the formation of intermetallic compounds; the ultimate tensile strength and yield strength increased by approximately 10% and 13%, respectively. Pr addition also refined the microstructure, and the hardness was recovered. The results herein demonstrate that the mechanical properties of Mg alloys are strongly influenced by their microstructure characteristics, including the grain size, volume fraction, and distribution of intermetallic phases.     

合金凝固组织对氢扩散和MH电极性能的影响

用电位阶跃法和恒电流充放电法研究了贮氢合金凝固组织中的氢扩散行为和合金氢化物（ＭＨ）电极放电的速度特性．研究表明：合金ＭＬＮｉ３．４５（ＣｏＭｎＴｉ）１．５５的各凝固组织中氢扩散系数及合金的电极性能均明显不同，随合金凝固时冷却速度增大，氢扩散系数和晶胞体积减小；合金电极的高倍率放电率主要取决于氢在合金中的扩散速度和电极表面的电催化活性．定向凝固组织具有良好的放电速度特性与其凝固组织中存在Ｎｉ的析出相关系密切．     

Peritectic solidification under high undercooling conditions

The solidification characteristics of highly undercooled Cu-7.77%Co peritectic alloy has been examined by glass fluxing technique. The obtained undercoolings vary from 93 to 203 K(0.14 TL). It is found that the α(Co) phase always nucleates and grows preferentially, which is followed by peritectic transformation. This means that the peritectic phase cannot form directly, even though the alloy melt is undercooled to a temperature far below its peritectic point. The maximum recalescence temperature measured experimentally decreases as undercooling increases , which is lower than the thermodynamic calculation result owing to the actual non-adia-batic nature of recalescence process. The dendritic fragmentation of primary α(Co) phase induced by high undercooling is found to enhance the completion of peritectic transformation. In addition, the LKT/BCT dendrite growth model is modified in order to make it applicable to those binary alloy systems with seriously curved liquidus and solidus lines. The dendrite growth velocities of primary α(Co) phase are subsequently calculated as a function of undercooling on the basis of this model.     

电流改变定向凝固单相合金枝晶间距机理

基于Ｍ－Ｓ理论的基本思路建立了电流作用下的凝固界面形态稳定性动力学微分方程式,并讨论了电流强度对稳定性及凝固过程达到稳定状态时所对应的扰动频率的影响。在此基础上讨论了电液改变定向凝固单相合金枝晶间距的机理。     

微合金钢初始凝固中奥氏体开始长大的温度

通过共聚焦激光显微镜对P510L钢的初始凝固过程进行了原位动态观察以考察δ相生成、包晶反应以及γ相的形成过程,并探索奥氏体开始长大温度.研究结果表明:1)冷却速度为25℃/s时P510L钢的冷却模式为首先从液相中析出δ铁素体,然后在液相与δ铁素体相之间发生包晶反应(L+δ→γ),进入三相共存区,液相消失后剩余的δ相通过固态扩散转变为γ相;2)在初始凝固过程中,奥氏体先进行一部分吞并、长大,然后才实现过剩δ铁素体向奥氏体的同素异构转变,最后实现完全奥氏体化;3)通过原位动态观察,探索了一种较为准确的确定原始奥氏体开始长大温度的实验方法,提高了奥氏体晶粒预测模型的准确性.