Energy-storage welding connection characteristics of rapidly solidified Cu-Co alloy foils

The connection characteristics of rapidly solidified Cu-40%Co alloy foils were studied using a self-developed micro-type energy-storage welding machine. The results show that the microstructure of the alloy foils is characterized by uniform and fine equiaxed grains, whose maximum grain size is 1.8μm. Under the optimum energy,the regular flat nugget is formed, low voltage and high capacitance are favorable for obtaining the perfect connection joints, whereas high voltage and low capacitance are likely to result in the surface burn of the alloy foils. With the increase of welding energy, the spot welding joint will be transformed from regular flat nugget to nugget-free one,and the microstructure tends to coarsen. The welding parameters recommended are, welding voltage 80 - 100 V,electric capacitance 1 800 - 2 500μF, and welding force 4 - 8 N.     

Decomposition processing and precipitation hardening of rapidly solidified Al-Cr-Y-Zr alloy

1　ＩＮＴＲＯＤＵＣＴＩＯＮＦｏｒｌａｓｔｔｗｏｄｅｃａｄｅｓｒａｐｉｄｌｙｓｏｌｉｄｉｆｉｅｄＡｌ Ｃｒ Ｚｒ( Ｍｎ)ｈｅａｔ ｒｅｓｉｓｔａｎｔａｌｕｍｉｎｕｍａｌｌｏｙｓｙｓｔｅｍｈａｓｂｅｅｎｐａｉｄａｐｕｂｌｉｃａｔｔｅｎｔｉｏｎｂｅｃａｕｓｅｏｆｉ     

Model for calculation of microstructural development in rapidly directionally solidified immiscible alloys

A model has been developed for the calculation of the microstructural evolution in a rapidly directionally solidified immiscible alloy.Numerical solutions have been performed for Al-Pb immiscible alloys.The results demonstrate that at a higher solidfication velocity a constituteional supercooling region appears in front of the solid/liquid interface and the liquid-liquid decomposition takes place in this region.A higher solidification velocity leads to a higher nucleation rate and ,therefore,a higher number density of the minority phase droplets.A s a result,the average radius of droplets in the melt at the solid/liquid interface decreases with the solidification velcity.     

Decomposition processing and precipitation hardening of rapidly solidified AI-Cr-Y-Zr alloy

Foil powders of AI-5.0Cr-4.0Y-1.5Zr ( % ) were prepared by using a multi-stage atomization-rapid solidification powder-maklng device. The obtained powders were exposed thermally at various temperatures. Variation of microstructures and properties of the alloy powders was investigated by micro-hardness measurement, X-ray diffraction, differantial thermal-analysis, and transmission electron microscopy with energy disperse X-ray analyses. The results show that cubic Al20Cr2Y ( a = 1. 437 nm) and metastable LI2 Al3Zr (FCC, a = 0. 405 1 nm) or equilibrium DO23 Al3Zr ( tetragonal structure, a = 0. 409 1 nm, b = 1.73 0 nm) are main second phases precipitated from supersaturated solid solution of the rapidly solidified foil powders during thermal exposure. The cubic dispersion precipitates prior to the two other Al3Zr type intermetallic phases in the course of the decomposition. Precipitation of incoherent Al20Cr2Y results in softening of foil powder, and coherent LI2 AI3Zr has imensive precipitation strengthening effect. The Al20Cr2Y phase is structurally stable, but it is prone to coarsen and polygonize above 450 ℃. Both Al3Zr type intermetallic phases have much smaller coarsening rate than Al20Cr2Y at temperature higher than 450℃. These two phases are able to keep their fine spherical morphologies up to 550℃, but Al3Zr transforms into DO23 structure from LI2 structure during thermal exposure above 550℃.     

Microstructures of AZ91D alloy solidified during electromagnetic stirring

With the help of an electromagnetic stirring device self-made and alloy melt quenching technology, the effect of electromagnetic stirring parameters on the microstructures of semi-solid AZ91D alloy was mainly studied at the stirring frequency of 200 Hz. The experimental results show that when the stirring power rises, the primary α-Mg rosettes in the semi-solid melt will bear stronger man-made temperature fluctuation and the root remehing effect of the dendritic arms is promoted so that the spherical primary α-Mg grains become much more and rounder. If the stirring frequency is 200 Hz, the ideal semi-solid microstructure of AZ91D magnesium alloy can be obtained when the stirring power is increased to 6.0 kW. If the stirring frequency is 200 Hz and the stirring power is 6.0 kW, it is found that the lower cooling rate is favorable for the spherical primary α-Mg grains to be developed during the electromagnetic stirring stage. If the AZ91D magnesium alloy billet prepared during electromagnetic stirring at the stirring frequency of 200 Hz and the stirring power of 6.0 kW is reheated to the solidus and liquidus temperature region,the primary α-Mg grain‘s shape will get more spherical, so it is very advantageous to the semi-solid thixoforming process     

Comparison of dendrite and dispersive structure in rapidly solidified Cu–Co immiscible alloy with different heat flow modes

Rapid solidification of Cu–Co immiscible alloy was investigated by glass-fluxing, spray casting and melt-spinning techniques. Both the transition from dendrite to dispersive structure and corresponding scale evolution were revealed and further elucidated in terms of the heat flow mode, nucleation and growth processes under different solidification conditions. With the increase of undercooling, columnar dendrite is replaced by dispersive structure due to the immiscible effect. In contrast, equiaxed dendrite forms in spray cast alloy due to multiple nucleation events and becomes thinner for the case of higher cooling rate. Ascribed to the enhanced non-equilibrium effect and insufficient period for collision and coagulation processes between separated droplets, fine globular dispersion appears upon the diameter of spray casting reaching 4 mm. As for the melt-spun ribbon with the highest cooling rate, a single-phase solid solution microstructure with refined grain of cellular morphology can be obtained, which is attributed to the suppression of liquid phase separation by instant solidification.     

Establishing the knowledge repository of rapidly solidified aging Cu-Cr-Zr alloy on the artificial neural-network

The non-linear relationship between parameters of rapidly solidified aging processes and mechancal and electrical properties of Cu-Cr-Zr alloy is available by using a supervised artificial neural network (ANN). A knowledge repository of rapidly solidified aging processes is established via sufficient data learning by the network. The predicted values of the neural network are in accordance with the tested data. So an effective measure for foreseeing and controlling the properties of the processing is provided.     

Crystallization process in rapidly solidified AI-Nd-Ni amorphous alloy prepared by melt spinning

Rapidly solidified ribbons of Al90Nd7Ni3 metallic glasses were prepared by using melt spinning. Crystallization process of the totally amorphous ribbons was investigated by differential scanning calorimetry and X-ray diffraction analysis, under continuous heating regime. The results show that, under continuous heating regime, the metallic glass devitrifies via two main stages: primary crystallization, resulting in two-phase mixture of a(Al) plus residual amorphous phase, and secondary crystallization, corresponding to some inter-metallic phases appearing,successively including A111 Nds, Als Ni, and some unknown phases, in the AI amorphous/crystal matrix. Four peaks appear on the continuous heating DSC curves. Their peak temperatures are respectively 470.8, 570.8, 585.6, and 731.6 K at infinitesimal heating rate, and their activation energies of the respective phase transformation are 183.0,294.7, 232.5 and 269.1 kJ/mol. The values of Avrami exponent of the four reactions decrease with increasing relative transformation degree. At the earlier stage of phase transformation, the values of n are larger than 4, and at the later stage the values of n become close to some value from 0.5 to 2.0.     

Microstructures of unidirectionally solidified Al-rich CuSi alloys

Aluminum-copper-silicon alloys lying in the monovariant through between the binary eutectic (Al)CuAl₂ and the ternary eutectic (Al)CuAl₂(Si) have been frozen unidirectionally over a range of rates from ca. 0.1 to 10 cm/hr and with imposed temperature gradients ranging from 150 to ca. 300°C/cm. The shapes of the growth fronts can be rationalized in terms of the ratio thermal-gradient/rate-of-solidification and the composition, as well as in binary alloys. The detailed morphologies of silicon are described for the different shapes of the solidification profiles, the six types of microstructures which appear in the AlSi alloys being formed, i.e., massive crystals, longitudinal fibers with or without lateral plates, complex-regular structures, complex-irregular structures, and polyhedral crystals.With regard to the CuAl₂ phase, the growth process is cooperative for planar and dendritic fronts. During cellular growth it appears as a semicontinuous matrix in which (Al) fibers are embedded. The conditions for existence of the observed microstructures are discussed with reference to the binary AlSi and AlCu systems.     

Crystallization process in rapidly solidified Al-Nd-Ni amorphous alloy prepa red by melt spinning

1　INTRODUCTIONIntherecentfew years ,Al richmetallicglasshasbeenpaidmoreandmoreattentiontointhenovelmaterialsresearchfield ,notonlyduetoitshighstrength ,hardnessandlowdensity ,butalsobecauseanew typeAl basednanophasecompositecanbeob tainedfromitbypartialcrystallization[17] .ManyAl basedamorphous/nanocrystallinealloyscontainingrareearth(RE =La ,Y ,Ce ,Nd ,etc)andtransitionmetal(TM =Fe ,Co ,Ni,etc)elementshaveanattractivecombinationofmechanicalproper ties .Ithasbeenreportedthatmanyofth…     

快速凝固Al-In偏晶合金的显微结构

采用单辊法快速凝固工艺制备均质的Ａｌ－Ｉｎ偏晶合金,并对所获得的快速凝固组织和形貌进行了观察和研究。结果表明,细小的Ｉｎ颗料均匀分布在Ａｌ基体中：在甩带厚度方向上,随着与激冷面距离的增大,Ｉｎ颗粒尺寸逐渐增大;在同一辊速条件下（同一冷却速率）,随着Ｉｎ含量的增加,Ｉｎ颗粒的平均尺寸也不断增大;同一成分条件下,随着辊速的升高,Ｉｎ颗粒的平均尺寸不断减少;单辊法快速凝固过程中第二相液滴通过Ｂｒｏｗｎｉ     

快速凝固Al-Pb合金的显微组织

采用单辊旋铸法分别制备了Al-5%Pb, Al-8%Pb和Al-15%Pb三种合金条带, 并利用TEM分析其显微组织. 结果表明 在快速凝固下, Al-Pb合金中的第二相(f.c.c. Pb)在基体中分布均匀, Pb颗粒尺寸随Pb含量增加而增加, 随冷却速度的增大而减小, Pb颗粒的尺寸呈双峰或三峰分布特征. 此外, 还分析了快速凝固下偏晶合金的凝固过程, 对上述现象进行了解释.     

快速凝固镁合金开发原理及研究进展

介绍快速凝固镁合金材料研究与开发的物理冶金原理及发展历程。在开发原理中着重介绍快速凝固镁合金的镁基固溶体扩展、新型弥散合金相的形成、晶粒及显微组织细化以及合金钝化等基础理论。在这些研发理论基础上，进一步阐述镁合金雾化快凝、模冷淬火和表面重熔这3种典型的快速凝固制备技术，举例说明了这3种快速凝固技术制备的多种镁合金的各项性能及显微组织特征。综合评价快速凝固技术制备镁合金材料的优势，说明快速凝固技术是开发新型镁合金材料，扩展镁合金在工程材料中应用的重要且具有发展前途的制备技术。     

快速凝固高硅铝合金粉末的热挤压过程

通过分析快速凝固高硅铝合金末在热挤压过程中的密度、微观组织和相结构的变化，对粉末热挤压成形机理进行了探讨，结果表明，快速凝固高硅铝合金粉末热压过程分为2个阶段，即填充挤压阶段和稳态渡动阶段，粉末生坯的致密化主要有在第一阶段完成，粉末颗粒中初晶Si相受到加热长大和挤压破碎两方面的综合作用，最终得到的挤压材料中的Si颗粒与原始粉末相比没有明显的相比，合金的相组成在挤压前后 有发生变化，快速凝固合 组织结构特征基本得以保留。     

快速凝固高硅铝合金加热过程中的组织转变

利用气雾化法制备高硅铝合金粉末,采用光学显微镜(OM)、扫描电镜(SEM)等现代测试手段,分析快速凝固高硅铝合金不同粒度粉末微观组织和结构特征,研究在不同加热温度和保温时间条件下针状富铁相的转变特性及β-Si相的粗化行为。结果表明:快速凝固高硅铝合金组织主要以基体上分布有大量细小的颗粒状和针状相为特征,合金粉末在加热过程中,随着温度的升高和保温时间的延长,颗粒β-Si相有粗化趋势,针状非平衡富铁相转变为棒状或颗粒状平衡相。通过台阶式连续加热模拟试验可获得针状相基本消失且颗粒β-Si相未发生明显粗化的组织。     

Microstructures and properties of rapidly solidified Mg-Zn-Ca alloys

Ternary alloys based on the Mg-Zn-Ca system were produced by twin-roll rapid solidification.The alloys were characterized by OM,SEM,HRTEM,XRD,EDS and Micro-hardness.The results show that the rapidly solidified flakes are of fine dendritic cell structures with the cell size ranging from 1 to 5μm.The Mg-6Zn-5Ca alloy in RS and annealing(200℃for 1 h) states are mainly composed ofα-Mg,Mg_2Ca,Ca_2Mg_6Zn_3 and a small quantity of Mg_(51)Zn_(20),MgZn_2 and Mg_2Zn_3.Micro-hardness increases with the increment of...     

快速凝固新型Au-Ag-Ge合金薄带的制备

采用单辊快速凝固法制备了Au-19.25Ag-12.80Ge合金薄带。利用TEM方法对合金薄带的显微组织进行了观察分析,根据热传输平衡方程对快速凝固过程冷却速率进行估算。结果表明:辊面线速度在18~24 m/s范围内时,快速凝固冷却速率可达8.93×105~1.293×106K/s,随着快速凝固冷却速率的增加,合金薄带厚度有所减小;单辊快速凝固工艺的冷却速率对合金薄带的显微组织有重要影响,由于快速凝固工艺增加了材料的固溶度,减小了成分偏析,细化了晶粒,因此显微组织更加均匀细小,形成了纳米晶,快速冷却工艺在金属熔液内垂直于辊轮方向上产生的冷却速度梯度,造成了晶粒内部应力集中现象的产生。     

Morphology and microstructure of rapidly solidified tin-lead alloy powders

Sn60Pb40 al oy powders were fabricated using the planar flow casting （PFC） atomization process. By using OM, SEM and EPMA, the characteristics of the morphologies and microstructures of the powders have been investigated. It is observed that the environment of ambient gas in the atomization box has great effects on the morphology of the al oy powders. The microstructures of Sn60Pb40 al oy powders produced by the PFC atomization process are completely composed of eutectic, which is made up of both oversaturated αsolid solution and β solid solution. The microstructures of smal size powders are extraordinarily undeveloped dendritic eutectic, in which the large majority of the α phase appears nearly spherical, evidently since the cooling rate is higher and the under-cooling is larger. As for the large size powders, since the cooling rate and undercooling are relatively low, lamel ar α phase apparently increases in the eutectic microstructures of these powders, and there is even typical lamellar eutectic structure clearly observed in some micro-areas. After remelting tests by DTA, the microstructures of smal size powders are transformed, which become composed of large crumby α phase and eutectic （α＋β）, while those of large size powders change into classical tin-lead structures of primary α phase plus lamellar eutectic （α＋β）. By studying the microstructures of tin-lead alloy powders, a model has been proposed to predict the microstructure formation of Sn60Pb40 al oy powders.