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快速冷却条件下Cu--Co合金的凝固

赵九洲 , 李海丽 , 何杰 , 张显飞

金属学报

利用气体雾化方法研究了Cu--20%Co (质量分数) 合金的快速凝固行为, 获得了富Co相以微细球形粒子形式分布于基体的合金粉末. 建立了Cu--Co雾化液滴快速凝固过程模型,模拟分析了雾化液滴凝固的动力学细节. 结果表明:所建模型能很好地描述Cu--Co合金雾化液滴冷却凝固过程;液--液相变过程中组织演变是弥散相液滴形核、长大、碰撞凝并和空间迁移共同作用的结果; 雾化液滴尺寸越大,冷却越慢, 富Co相液滴的形核速率越低, 凝固后富Co相的弥散度越差.

关键词: Cu-Co合金 , Rapid solidification , Atomization , Modeling

Modeling and Simulation of the Microstructure Evolution of the Gas-atomized Alloy Droplets during Spray Forming

Jiuzhou ZHAO , Dongming LIU , Hengqiang YE

材料科学技术(英文)

In order to understand the solidification process of an atomized droplet and predict the fraction solidification of droplets with flight distance during spray forming, a numerical model based on the population dynamics approach is developed to describe the microstructure evolution under the common action of the nucleation and growth of grains. The model is coupled with droplets heat transfer controlling equations and solved for Al-4.5~wt~pct Cu alloy. It is demonstrated that the numerical results describe the solidification process well.

关键词: Rapid solidification , null , null , null

Microstructure Evolution of Cu-Pb Monotectic Alloys Processed in Drop Tube

Chongde CAO , Bingbo WEI

材料科学技术(英文)

Rapid solidification of Cu-Pb monotectic alloys has been accomplished during free fall in a 3 m drop tube. Both macrosegregated and uniformly dispersed structures are observed in Cu-40 wt pct Pb alloy droplets, whereas droplets of composition Cu-64 wt pct Pb exhibit only macrosegregation morphologies. The microstructures are strongly dependent on droplet size. The higher undercooling tends to facilitate liquid phase separation and results in more extensive macrosegregation in smaller droplets. There exists a pronounced tendency for the Pb-rich liquid to occupy the surface of the droplets of both compositions, resulting from the quite lower surface tension of the Pb-rich phase and causing a Pb-rich layer at the surface of the solidified droplet. The nucleation of monotectic cells in the Cu-40 wt pct Pb droplets with dispersed structures preferentially occurs at the droplet surface. A single nucleation event takes place more frequently as droplet size is reduced.

关键词: Rapid solidification , null , null , null , null , null

Energy-storage Welding Connection Characteristics of Rapid Solidification AZ91D Mg Alloy Ribbons

Jinfeng XU , Qiuya ZHAI , Sen YUAN

材料科学技术(英文)

Energy-storage welding connection characteristics of rapidly solidified AZ91D Mg alloy ribbons with 40~70 μm thickness are investigated using a microtype energy-storage welding machine. The microstructure and performance of the connection joints are analyzed and studied. The research results indicate that energy-storage welding is able to realize the spot welding connection of AZ9ID Mg alloy ribbons. The welding nugget consists of developed α-Mg equiaxed grains with the sizes of 1.2~2.7 μm and intergranular distributed β-Mg17Al12 compounds. The thickness of bond zone is about 4 μm and the solidification microstructure is characterized by the fine equiaxed grains with the sizes of 0.8~1.2 μm, and grain boundary has become coarsening. The columnar crystal in HAZ also becomes slightly coarsening and the grain boundary has broadened, however, there is no obvious change in its primitive morphology and crystallographic direction. When welding energy is about 2.0 J, the welding joints with higher shear strength and smaller electrical resistivity are obtained.

关键词: AZ91D , null , null , null , null

Effect of Brownian Coagulation on the Liquid-liquid Decomposition in Gas-atomized Alloy Drops

Jiuzhou ZHAO

材料科学技术(英文)

Modeling and simulation have been carried out for Al-Pb alloys to investigate the Brownian coagulation effect on the microstructure development in a gas-atomized drop during the liquid-liquid decomposition. The results indicate that Brownian coagulation has a weak effect on the nucleation and a relatively strong effect on coarsening the minority phase droplets. The influence of Brownian coagulation on the liquid-liquid decomposition decreases with the increase in the diameter (or the decrease in the cooling rate) of the atomized drop.

关键词: Immiscible alloy , null , null , null , null

Microstructre of Mg-6.4Zn-1.1Y Alloy Fabricatec by Rapid Solidification and Reciprocating Extrusion

Z.M. Zhang , C.J. Xu , X.F. Guo

金属学报(英文版)

In order to explore the methods to prepare high-strength quasicrystal-reinforced magnesium alloys, the flakes of rapidly solidified Mg-6.4Zn-1.1Y magnesium alloy with thickness of 50-60冚m were obtained by a melt spinning single-roller device, and then the flakes were processed into rods by reciprocating extrusion and direct extrusion. The microstructure of the alloy was analyzed by optical microscope and SEM, and the constituent phases were identified by XRD. Phase transformation and its onset temperature were determined by differential thermal analyzer (DTA). The analysis result shows that rapid solidification for Mg-6.4Zn-1.1Y alloy can inhibit the eutectic reactions, broaden the solid solubility of Zn in 冄-Mg solute solution, and impede the formation of Mg3Y2Zn3 and MgZn2 compounds, and thus help the icosahedral Mg3YZn6 quasicrystal formed directly from the melt. The microstructure of the flakes consists of the -Mg solid solution and icosahedral Mg3YZn6 quasicrystal. Dense rods can be made from the flakes by 2-pass reciprocating extrusion and direct extrusion. The interfaces between flakes in the rods can be welded and jointed perfectly. During the reciprocating extrusion and direct extrusion process, more Mg3YZn6 compounds are precipitated and distributed uniformly, whereas the rods possesses fine microstructures inherited from rapidly solidified flakes. The rods contain only two phases: 冄-magnesium solid solution as matrix and fine icosahedral Mg3YZn6 quasicrystal which disperses uniformly in the matrix.

关键词: Magnesium alloy , null , null , null

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