连续冷却搅拌A2017半固态合金流变行为研究

采用回转式熔体物性综合测试仪测定了A2017合金半固态浆料在连续冷却搅拌条件下的表观黏度变化,对其组织变化进行分析,研究了连续冷却搅拌条件下A2017合金半固态浆料的流变行为.实验结果表明,连续冷却搅拌条件下,A2017合金半固态浆料的表观黏度随固相率的增大而增大;在固相率一定的情况下,降低冷却速度或增大剪切速率,均导致表观黏度降低.显微组织观察表明,半固态浆料的流变行为与其微观组织结构有很强的关联,降低半固态浆料温度,浆料固相颗粒含量增加,表观黏度增大;降低冷却速度或增大剪切速率有利于半固态浆料固相颗粒形态向非枝晶形态的转变,因而半固态浆料表观黏度降低,流动性好.     

电磁搅拌的半固态60Si2Mn钢流变轧制的组织特征

为了研究半固态钢铁材料轧制成形工艺，采用60Si2Mn弹簧钢作为实验材料，对其进行1道次的半固态轧制变形，研究了半固态浆料轧制前、后的组织变化，明确了在轧制变形区中半固态浆料的组织变化特征，研究结果表明：经1道次半固态轧制变形后，半固态浆料的组织得到明显改善，同时半固态浆料中的液、固相产生分离，固相颗粒大多聚集在轧制的中间区域，液相主要流向轧件的边部而导致液相偏析，使轧制产品的边部和中部的组织分布不同；当固相率达到一定值时，固相颗粒才发生塑性变形，被压扁拉长。     

半固态60Si2Mn流变轧制的组织及性能

对弹簧钢（60Si2Mn）进行1道次的半固态轧制变形，研究半固态浆料轧制前后的组织和性能，明确了在轧制变形中半固态浆料的组织变化规律和轧后的力学性能特征，结果表明：仅经过1道次的半固态轧制变形，兰固态浆料的组织就得到了明显的改善；在半固态浆料中，固相颗粒大多聚集在轧件的中间区域，液相主要流向轧件的边部，从而导致液相偏析，使轧制产品的边部和中部的组织和性能的不同，只有当固相率达到一定数值时，固相颗粒才会发生塑性变形，被压扁拉长。     

双螺杆机械搅拌半固态镁合金的组织与性能

采用双螺杆机械搅拌制浆机和半固态流变压铸成形工艺制备AZ91D镁合金半固态浆料，研究了材料性能与微观组织之间的关系．结果表明，随着镁液的浇注温度或搅拌机简体温度的降低，半固态浆料的固相率越高，初生α-Mg相晶粒变得更细小和圆整，简体温度比镁液浇注温度的影响更显著．当浆料固相率控制在30％-45％时，半固态流变压铸成形镁合金铸件具有较高的抗拉强度和延伸率；随着晶粒平均尺寸的增加，材料的力学性能逐渐降低．提出了高剪切速率下流变压铸成形非枝晶组织的形成机理．     

机械搅拌器对C-SiC/Cu半固态浆料中石墨颗粒和SiCP的影响

利用直桨叶搅拌器在圆柱坩埚内机械搅拌C-SiC/Cu半固态浆料,研究搅拌速度为200 r/min、搅拌器上下移动速度为10 mm/s时C-SiC/Cu半固态浆料中石墨颗粒和SiC颗粒(SiC_P)的均匀性。结果表明:直桨叶与水平面的夹角γ与两种颗粒在坩埚顶部和底部含量偏差都存在二次关系,当γ=30°时石墨颗粒和SiC_P在坩埚中轴向分布均匀,但同一水平面内的SiC_P仍存在偏聚现象,说明SiC_P的偏聚是导致常规直桨叶机械搅拌C-SiC/Cu半固态浆料整体不均匀的主要原因;利用双层桨叶搅拌器代替常规直桨叶搅拌器,通过调整叶片层间距h,当h=10~20 mm时可以消除SiC_P的偏聚现象;通过对单层桨叶搅拌器和双层桨叶搅拌器机械搅拌铸造获得的C-SiC/Cu复合材料进行磨损试验发现,单层桨叶搅拌器不同部位磨损率存在差异,双层桨叶搅拌器磨损率几乎相同。说明SiC_P的偏聚可以通过增大机械搅拌剪切力度得以消除,利用双层桨叶搅拌器进行机械搅拌可以获得均质的C-SiC/Cu半固态浆料。      

多孔介质模型镁合金流变铸轧LBM模拟

根据REV尺度多孔介质格子-Boltzmann方法基本理论,建立求解高固相率半固态浆料渗流过程的热流耦合数值模型.应用模型对变孔隙率Poiseuille流动及纯扩散凝固进行模拟.LBM模拟结果与有限差分模拟吻合.分析了压差作用下浆料在平板间渗流冷却与热流耦合过程.模拟结果表明浆料渗流速度随温度降低而减慢,相同时刻下凝固潜热较大的浆料渗流Re数高.利用提出的模型初步探索了AZ91D镁合金半固态流变铸轧过程的热流场分布.     

辅助电磁场作用下的铝基复合材料钎焊接头界面微观组织及其分析

采用Zn-Al钎料,以铝基复合材料SiC/A356为研究对象,对该材料辅助电磁场作用下的钎焊工艺及其接头界面微观行为进行了探索性的研究。试图通过电磁场效应,控制液固界面处强化相的推斥/吞没行为,并对不同交变方波电流峰值作用下的接头微观组织进行分析。研究结果表明,在磁场强度为0.5T,交变电流频率为100Hz,电流峰值为70A时SiC强化颗粒的行为得到了有效的控制,避免了SiC强化相颗粒在界面处的偏聚行为,获得了SiC强化相颗粒在钎缝中均匀分布的铝基复合材料钎焊接头。     

原位Mg2Si／AM60镁基复合材料半固态组织演变

采用原位合成技术制备了Mg2Si/AM60复合材料.研究了不同搅拌工艺参数对半固态镁基复合材料显微组织的影响.结果表明,镁合金中加入结晶Si后,生成了中国汉字状的Mg2Si增强颗粒.对复合材料在半固态温度区间进行机械搅拌,研究发现,搅拌温度越高,搅拌速度越大,固相颗粒越细小、均匀和圆整,但温度太高,固相颗粒会熔化,随搅拌时间的延长,固相颗粒先变得细小、均匀和圆整,然后长大.     

半固态AlSi4Mg2铝合金的稳态流变性能

利用Couette型同轴双简流变仪检测了半固态AlSi4Mg2合金浆料的等温稳态表观粘度．结果表明：半固态AlSi4Mg2合金浆料的稳态表观粘度随着固相分数的增加而增大，并且当固相分数达到某一临界值之后迅速增大．当固相分数较低时，半固态AlSi4Mg2合金浆料的粘滞力主要来自液态合金的粘度，但随着固相分数的增加，固相颗粒之间以及与液相之间的碰撞和摩擦变得越来越强烈，使得合金浆料的表观粘度越来越高．半固态AlSi4Mg2合金浆料的稳态表观粘度随着剪切速率的增大而减小，并且随着剪切速率的提高，表观粘度急剧增大，所对应的临界固相分数也随着增大．当剪切速率很高时，固相颗粒的形状更加趋于球化，浆料的粘滞力下降，浆料的表观粘度就更小．半固态AlSi4Mg2合金浆料的稳态表观粘度ηa与固相分数fs和剪切速率γ之间的关系可以近似地表示为ηa=25.5exp（6.13fs）γ^-1.16     

高碳工具钢半固态流变轧制

探讨了高碳工具钢常规的加工方法和半固态流变轧制技术，结果表明将在凝固过程中进行搅拌后制备的高碳工具钢半固态浆料直接进行流变轧制，可生产出成分均匀、没有偏析的产品，消除了在常规轧制中很难克服的网状碳化物等缺陷；半固态固相颗粒细小而且呈球状可生产出高强、高韧性的工具钢。半固态轧制有可能成为未来高碳工具钢生产的一种新工艺。     

Preparation QTi3.5-3.5 Graphite Lubricant Material with Semi-solid Casting Technology

For the first time, the distribution of graphite particles in QTi3.5-3.5 graphite ingot was studied by using semi-solid casting technology. The results show that: the relationship between solid fraction and stirring temperature of QTi3.5-3.5 graphite slurry is y=759.4-0.711x (where y is solid fraction, x is stirring temperature). With the increasing of solid fraction of QTi3.5-3.5 graphite slurry, the agglomeration of graphite particles in ingot reduces gradually. The condition to prepare QTi3.5-3.5 graphite lubricant material with even distribution of graphite particles is that the solid fraction of QTi3.5-3.5 graphite slurry is larger than 40%.     

Preparation QT3.5-3.5 graphite lubricant material with semi-solid casting technology

For the first time, the distribution of graphite particles in QTi3.5-3.5 graphite ingot was studied by using semi-solid casting technology. The results show that: the relationship between solid fraction and stirring temperature of QTi3.5-3.5 graphite slurry is y=759.4-0.711x (where y is solid fraction, x is stirring temperature). With the increasing of solid fraction of QTi3.5-3.5 graphite slurry, the agglomeration of graphite particles in ingot reduces gradually. The condition to prepare QTi3.5-3.5 graphite lubricant material with even distribution of graphite particles is that the solid fraction of QTi3.5-3.5 graphite slurry is larger than 40%.     

Influence of Solid Fraction on Structure of QTi3.5-15/Graghite Slurry

The electromagnetic-mechanical stirring technology was used to prepare QTi3.5-15/graghite slurry. The distribution of graphite particies in QTi3.5-15/graghite slurry was studied using cold quenching method. The results show that solid fraction of QTi3.5-15/graphite slurry increases with the decreasing of stirring temperature. There is a linear relationship between solid fraction and stirring temperature. With the increasing of solid fraction, the distribution of graphite particies in slurry becomes uniform gradually. When the solid fraction is larger than 45%, the rising of graphite particies in slurry can be restricted, and QTi3.5-15/graghite slurry with uniform distribution of graphite particies can be prepared.     

Semi-solid Pressing Bonding Strength between Steel and Cu-graphite Composite

The pressing bonding of steel plate with QTi3.5-3.5graphite slurry was studied. The relationship among preheating temperature of steel plate, preheating temperature of dies, solid fraction of QTi3.5-3.5graphite slurry, and interfacial shear strength of bonding plate could be established with artificial neural networks perfectly. This model could be optimized with a genetic algorithm. The results show that the optimum bonding parameters are: 618℃ for preheating temperature of steel plate, 526℃ for preheating temperature of dies and 46.2% for solid fraction of QTi3.5-3.5graphite slurry, and the largest interfacial shear strength of bonding plate is 128.3 MPa.     

Effect of Relative Reduction on Property of Steel-Mushy Cu-Graphite Composite

The rolling treatment of steel-mushy QTi3.5-3.5 graphite composite was conducted under different relative reduction at room temperature. The effect of room-temperature rolling on interfacial mechanical property of steel-mushy QTi3.5-3.5 graphite composite was studied and the relationship between interfacial shear strength and relative reduction was established. The results show that, for steel-mushy QTi3.5-3.5 graphite composite, which consists of 1.2 mm-thick 08AI steel plate and 2.8 mm-thick QTi3.5-3.5 graphite layer, there is a nonlinear relationship between interfacial shear strength and relative reduction in graphite layer. When relative reduction is smaller than 1.1%, interfacial shear strength increases with increasing the relative reduction. When relative reduction is larger than 1.1%, interfacial shear strength decreases with increasing the relative reduction. When relative reduction is 1.1%, the largest interfacial shear strength of 145.2 MPa can be obtained.     

Influence of Pressing Time on Steel-copper-graphite Bonding

The bonding of steel plate with QTi3.5-3.5 graphite slurry was studied by using pressing bonding technique. The influence of pressing time on the interracial mechanical property of bonding plate was researched. The results show that： under the conditions of 620℃ preheating temperature of steel plate, 530℃ preheating temperature of dies, 46% solid fraction of QTi3.5-3.5 graphite slurry and 50 MPa pressure, there exists a nonlinear relationship between pressing time and interracial shear strength. The interracial shear strength of bonding plate increases with increasing pressing time and reaches a largest value about 127 MPa when pressing time is longer than 120 s. At the interface with the best mechanical property, there exists a continuous Fe-Cu inter-diffusion zone and a metallurgical bonding.     

Study of machinable SiC/Gr/Al composites

The effect of flaky graphite particles [with volume fraction (vf) 3–7%] on machinability and mechanical properties of SiC/Al composites were investigated. Results showed that the machinability was improved greatly with the increasing vf of graphite particles. When the vf of graphite particles was 7%, the tool life was prolonged by 130%, and the tensile strength and elastic modulus of SiC/Gr/Al composite were 365 MPa and 144 GPa, respectively. The presence of flake graphite particle acted as solid lubrication and promoted chip formation during cutting, resulting in an improved machinability.     

Solid electrolyte/graphite composite particle for an all-solid-state lithium-ion battery

A great issue in the development of an all-solid-state lithium-ion battery (ASSLIB) is the fabrication of a composite electrode with good contact between active materials (AMs) and solid electrolytes (SEs). To overcome this challenge, it is important to develop a powder processing technology that produces composite particles of AMs and SEs. In this study, we investigated a dry impact blending process for producing graphite composite particles (typical anode AM) and sulfide SEs. First, by controlling the rotating speed of the rotor in the dry impact blending process, two types of composite particles, namely surface-coated (SC) composite particles with no graphite breakage and matrix-type (MT) composite particles with graphite breakage, were produced. The SC composite particles showed higher electrochemical performance than the MT composite particles due to less change in the graphite crystallinity. Second, the longer the processing times for the preparation of SC composite particles, the higher the SE coating on graphite, resulting in higher electrochemical performance. Third, we demonstrated that the SC composite particles exhibited higher electrochemical performance than those prepared using a conventional lab-scale mixing technique. We demonstrated the effectiveness of the dry impact blending process for the preparation of an anode composite electrode for ASSLIBs.     

膨胀石墨/石蜡相变复合材料有效导热系数的数值计算

通过膨胀石墨粉与石蜡混合制备相变复合材料可有效提高该储能材料的传热性能。为研究膨胀石墨/石蜡相变复合材料的导热机制,提出了膨胀石墨粉与石蜡混合后的3尺度层次固体有效导热系数计算方法。然后,通过数值模拟计算得到了具有不同体积分数和不同导热系数的膨胀石墨导热颗粒的膨胀石墨/石蜡相变复合材料的有效导热系数。结果表明:膨胀石墨能够有效地提高石蜡的导热性能,当膨胀石墨的体积分数为10%时,膨胀石墨/石蜡相变复合材料的有效导热系数是纯石蜡的9倍。此外,提高底层尺度的石墨片与石蜡的混合程度及降低底层尺度石墨的体积分数都能有效提高膨胀石墨/石蜡相变复合材料的有效导热系数。所得结论为探究膨胀石墨粉提高相变复合材料导热系数的机理奠定了基础。     

Formation of a graphite-rich zone in centrifugally cast copper alloy graphite composites

The formation of the graphite-rich zone in centrifugally cast copper alloy containing originally 7 and 13 vol % graphite particles, cast at 800 and 1900 r.p.m. was studied as a function of the rotational speed of the mould and the volume fraction of graphite particles. The calculated recovery of graphite particles in copper alloys was found to be around 99% and 95%, for 7 and 13 vol% graphite particles originally added to the melts, respectively. The ratio of the thickness of graphite-rich zone to the casting thickness was observed to increase with increasing volume fraction of graphite particles and with decreasing rotational speed of the mould. These ratios were found to be between 0.56 and 0.76 for centrifugal casting of copper alloy containing 7 and 13 vol % graphite particles, respectively, cast at 800 r.p.m.; the corresponding ratios were between 0.42 and 0.71, respectively, for the alloys cast at 1900 r.p.m. The ratio of the thickness of the graphite-rich zone to the casting thickness has been discussed in terms of the velocity of the particle and the solid/liquid interface. © 1998 Chapman and Hall