Microstructure and mechanical properties of hypereutectic Al-Fe alloys prepared by semi-solid formation

The effects of alloying elements, electromagnetic stirring, reheating and semi-solid formation on the microstructure and mechanical properties of Al-Fe alloys prepared by semi-solid formation were studied. It was found that alloying elements and electromagnetic stirring can alter the morphology and growth mode of the iron-rich phase in Al-Fe alloys; and effectively refine the primary Al3Fe phase. In contrast to the microstructure obtained in conventional casting, the Al3Fe phase becomes thin short rod-like instead of thick needle-like; and the dendritic grain structure almost disappears in the semi-solid formation. The Al3Fe phase can be further refined through being dissolved or fused during subsequent reheating. It was also found that the larger extrusion ratio of semi-solid formation causes a greater crushing effect and therefore the Al3Fe phase is more refined and has more uniform distribution. Moreover, Al-Fe alloys prepared by semi-solid formation exhibit excellent mechanical properties at both room and high temperatures.

Formation regularity of phases in nanometer powders of Al-Fe alloy prepared by gas evaporation

Nanometer powders of Al Fe alloy were prepared by gas evaporation. The formation regularity of the phases in the as prepared powders and the morphology of the particles were examined. The experimental results show that chemical composition of the master alloy is the key factor which controls the chemical composition of the compound phases in nanometer powders at given evaporating temperature, the compound phases with high Fe mole fraction will form with increasing of Fe content in master alloy. Only Al 13 Fe 4, FeAl 2 and Al 2Fe compound phases form in nanometer powders in present experiment, changing of the pressure of Ar can only alter relative amounts of the compound phases in the powders. Nanometer particles with inhomogeneous tissue were obtained, which is very different from that of pure Al and Fe nanometer particles. When mole fraction of Fe in particles increases, the inhomogeneity is enhanced. [

Effect of Spark Plasma Sintering on Microstructures and Properties of Al-Fe Alloy

2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering parameters included sintering temperature,heating or cooling rates,pressure and holding time. 300 ℃- 800 ℃ were adopted while the heating or cooling rate was 100 ℃ / min and with the pressure of 50 MPa in the experiments. The holding time was 10 min or 20 min at different temperatures, respectively. Bulk materials after sintering were examined by Scanning Electron Microscopy and X-Ray Diffraction. The micro-hardness and relative density also were tested. The sintering temperature had the most significant influence on the microstructure and property of the bulk material. The influence of holding time came second while the heating or cooling rates and pressure were fixed. The density became larger with the increase of the temperature. The compactness was best at 500℃. The pressure and generation of high-temperature phases were the factors which affected the density and the compactness.

Model on medium range order in liquid Al-Fe alloys

Numerical analysis confirms that in some cases the prepeak in the structure factor causes obvious change in the coordination number, but change in the interatomic distance can be neglected for the study of the medium range order(MRO). In order to model the MRO, it is not possible to get enough information based on the pair correlation function; however the quasi-Bragg equation can be employed to characterize the quasi-period of MRO corresponding to the prepeak position. By assuming that the interatomic distance between Fe and Al atoms hardly varies with composition, structural models were constructed based on the B2-type structure units of ordered FeAl alloy. The quasi-periods for different alloys obtained from the model structures are in reasonable agreement with the experimental ones.

Structure of medium-range order in molten Al-Fe alloy

The molecular-dynamics (MD) simulation was carried out to investigate the structure of medium-range order (MRO) of a liquid Al 5Fe 2 alloy. Prepeak is observed in the structure factor S(Q), which is considered as the signature of MRO. Results from MD simulation and experiment agree well with each other, which proves reliability of the simulation. It is found from the calculated Ashcroft-Langreth structure factors that there exists strong interactional force between atom Al and Fe, which results in the great concentration fluctuation, i.e. the chemical order, in the liquid Al 5Fe 2. Both the chemical order parameter, α , and the Bhatis-Thornton(BT)structure factors indicate the preference for unlike-neighbor bonds. It is seen from the low-Q domain of S(Q) and the concentration-concentration structure factor S CC(Q) that the prepeak mainly comes from the first peak of S CC(Q). The structural model, which reflects the characteristic of MRO, is also constructed .

不同形貌Al-Fe金属的块体压制成形模拟研究

文章以含40%Al的Al-Fe复合金属为研究对象,对颗粒状和屑状40Al-Fe复合金属分别进行压制预变形,并对屑状40Al-Fe复合金属预制坯进行了二次热压缩变形,重点研究压制预变形及二次热压缩对Al-Fe复合金属成形性和界面影响。结果表明:压力为16 MPa时,颗粒状40Al-Fe复合金属预制坯(密度为4.54 g/cm^(3))成形性良好且形成致密界面;压力为16 MPa时,屑状40Al-Fe复合金属预制坯(密度为3.50 g/cm3)可以成形但界面存在孔洞,Al屑主要为“片层状”“狗牙状”“圆圈状”“波浪状”,其经二次热压缩变形,“圆圈状”Al屑连成一个整体,“狗牙状”与“波浪状”Al屑均演变为“片层状”,而Fe屑仍为“片层状”“块状”,未发生明显变形。变形温度300℃、变形速率0.5 s^(-1)、变形程度0.1是目前生产工艺最佳参数,此时屑状40Al-Fe复合金属成形性最佳且界面结合良好(密度为4.66 g/cm^(3))。

Influence of rare earth cerium on the microstructures and performances of Al-Fe alloy

The effects of rare earth addition on the microstructures as well as the tensile performances and electrical conductivity of Al alloys have attracted increasing attention recently.However,little research has been carried out to investigate the influence of minor Ce(the Ce additive amount is below 0.1 wt.%).In this study,experiments have been performed to explore the effects of minor Ce on the microstructures as well as the tensile properties and the electrical conductivity of Al-Fe alloy.The results demonstrate that minor rare earth Ce addition not only leads to the α-Al refinement and the modification of Al_(13)Fe_(4) minority phase,but also decreases the solid solubility of Si.The grain refinement induced by Ce addition has a negligible influence on the tensile strength and yield strength,while the ductility and conductivity can be simultaneously ascended by adding rare earth Ce.The modification of Al_(13)Fe_(4) minority phase is responsible for the increment of ductility,and the diminution of Si solid solubility in the Al matrix leads to the increase of electrical conductivity.This work provides a strategy for concurrently improving the tensile performances and electrical conductivity of aluminum alloy.

电缆用Al-Fe系铝合金导体材料的恒应力高温压缩蠕变行为

对电缆用Al-Fe系铝合金导体材料进行恒应力(63.6,72.6,78.3,84.7 MPa)高温(90℃)压缩蠕变试验,研究了压缩应力σ对稳态蠕变速率ε·的影响,建立了压缩蠕变本构方程,分析了压缩蠕变机制。结果表明:铝合金试样的稳态蠕变速率随着压缩应力的增加成倍增大;90℃下铝合金试样的蠕变本构方程为ε·=σ^(9.27)e^(-52.2),拟合曲线和试验结果的相关系数达0.9976;铝合金蠕变过程中存在门槛应力,其值为34.2 MPa,引入门槛应力对蠕变方程进行修正,修正方程计算所得稳态蠕变速率与试验值的相对误差为8%,证明模型准确,得到的真应力指数为5,说明电缆用Al-Fe系铝合金导体材料在90℃下的压缩蠕变行为是由位错攀移机制主导的第二相粒子强化类蠕变。

Micro-inhomogeneous structure of liquid Al-Fe alloys

Using X-ray diffraction, the structure factors of molten Al-Fe alloys were determined as a function of composition at a constant 1 550℃. The nearest neighbour distance and coordination number are given. Both structure factors and total density functions could be well reproduced by a micro-inhomogeneous model. The entire concentration region can be divided into four intervals with Al, Al7Fe, Al5Fe2,Fe3Al and Fe acting as borders. Alloys situated at the borders of the concentration intervals contain clusters of one type whose composition represents that of the alloy in question. The alloys between the borders contain clusters of the two border types.

Comparison of contribution of sub-rapid cooling and shear deformation to refinement of Fe-rich phase in hypereutectic Al-Fe alloy during rheo-extrusion

A hypereutectic Al-3Fe(wt.%)alloy was subjected by rheo-extrusion,and the effect of sub-rapid cooling and shear deformation on the refinement of Fe-rich phase was investigated.The results showed that both the primary Fe-rich phase and eutectic Fe-rich phase in the solidified Al-Fe alloy were finer than the platelike Fe-rich phase in the as-cast Al-Fe alloy with the same content of Fe.The solidified Al-Fe alloy was subjected to three stages of shear deformation,and both the primary Fe-rich phase and eutectic Fe-rich phase were fractured and the average length was refined to 400 nm,while Fe-rich phase in the as-cast Al-3Fe(wt.%)alloy was platelike and its average length was 40 pm.The tensile strength and elongation of the hypereutectic Al-3Fe(wt.%)alloy containing nanosized Fe-rich phase were 162 MPa and 25.78%while those of the as-cast AI-3Fe(wt.%)alloy containing coarse platelike Fe-rich phase were 102 MPa and 16.84%,respectively.In the refineme nt of Fe-rich phase in hypereutectic Al-Fe alloy during rheo-extrusion,the three stages of shear deformation contributed more than sub-rapid cooling.

Influence of Si content and heat treatment on microstructure of Al-Fe-Si alloys

The effect of Si addition and heat treatment on the Al-5wt.%Fe alloy has been investigated by OM, SEM-EDS and XRD. The results show that the Si plays a significant role in refining the primary Al3 Fe phase. It was found that the addition of 3.0wt.% Si made the alloy present the finest and well-distributed primary Al3 Fe phase, but the Al3 Fe phase almost disappeared when 5wt.% Si was added. With further increase in the Si content, some Fe-rich phases appeared in the inter-grains and coarsened. In addition, the heat treatments exert a significant impact on the microstructural evolution of the Al-5wt.%Fe-5wt.%Si alloy. After heat treatment for 28 hours at 590 oC, the coarse platelet or blocky Fe-rich phase in Al-5wt.%Fe-5wt.%Si alloys was granulated; the phase transformation from metastable platelet Al3 FeSi and blocky Al8Fe2 Si to stable Al5 FeSi had occurred. With the extension of heat treatment, the Si phase coarsened gradually.

半固态连续成形Al-Fe合金的工艺参数优化及组织性能分析

针对Al-Fe合金半固态连续成形工艺中挤压轮转速、挤压温度、Fe元素质量分数等参数进行优化。结果表明:当挤压轮转速为10 r·min-1、挤压温度为690℃、合金中Fe元素质量分数为1.00%时,可获得较好的Al-Fe合金线材质量。采用扫描电镜(SEM)、扫描电镜能谱分析(EDS)及透射电镜(TEM)对半固态连续成形最优工艺条件下制备的Al-Fe合金进行微观组织分析,确定了第二相成分,并分析了半固态连续成形工艺对含铁相的细化作用。经拉伸力学性能测试,Al-Fe合金线材屈服强度为85 MPa、抗拉强度为142 MPa、延伸率为35%;SEM测试表明拉伸断口形貌为韧性断裂。

Effect of Cerium on Chemical Short Range Order of Al-Fe-Ce Amorphous Alloy

The chemical short range order of Al Fe Ce amorphous alloy was studied by means of X ray diffraction(XRD) and differential scanning calorimetry(DSC). It is found that the prepeak position in X ray diffraction intensity curve shifts to higher angles as the content of Fe increases, but it shifts to smaller angles as the content of Ce increases. The crystallization character of the amorphous alloy changes with the variation of the content of Fe and Ce. Ce can improve the interaction between atoms and the capacity of compound formation, so it is favorable to Al based glass formability.

FORMATION OF QUASICRYSTALLINE PHASE IN RAPIDLY SOLIDIFIED Al-Fe-V-Si ALLOY

The icosahedral quasicrvstalline phase (i-phase)with the chemical composition of 82.4at%Al,8.8at%Fe,3.6at%V and 5.2at%Si in melt spun Al-Fe-V-Si ribbons was found.It is suggested that the temperature and holding time of the melt prior to quenching are the important factors in the formation of the i-phase.

Fe含量对Al-Fe压铸铝合金导电率及机械性能的影响

为实现汽车零部件对压铸铝合金导电性、强度、成型性和低成本的需求,以Al-Fe系合金为基础,研究了Fe含量对压铸铝合金导电率和机械性能的影响,进行了微观组织分析和高温性能稳定性验证,并探究了热处理工艺的影响。结果表明,Al-(0.25%~3.0%)Fe-0.02%B(质量分数)合金具有良好的压铸成型性,添加Fe可显著提升合金的强度且不造成导电率的大幅下降,Fe含量从0.25%增加到3.0%(质量分数)后,抗拉强度增加130%,导电率仅下降17%。在高温工况下,材料导电率和抗拉强度仅略微下降,表现出较好的高温稳定性。时效处理后导电率提升约1.4%IACS,强度提升约7 MPa。Al-Fe系合金是适合开发兼具高导电、中强度、低成本、可压铸等特点的合金体系。

Effect of quenching condition on micro inhomogeneous structure of Al-Fe-Ce amorphous alloy

The microstructures of liquid and amorphous Al 90 Fe 5Ce 5 alloys were studied by X ray diffraction (XRD), and the crystalline behavior of the amorphous alloy was also investigated by differential scanning calorimetry (DSC). The distinct pre peaks were found on the structure factors of the liquid and amorphous alloys. The quenching temperature affects the pre peak area, but does not affect its position. The reduction of quenching temperature decreases the crystallization temperature and the activation energy of the Al Fe Ce amorphous alloy. Quenched from 1 050 ℃, a novel structure with a fine dispersion of Al nanophase particles homogeneously distributed in the amorphous matrix was obtained. And the sensitivity of the Al Fe Ce amorphous alloy to the quenching temperature reflects the micro inhomogeneity of the melt.

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A Ni_3Al-Fe BASED ALLOY

The microstructure,tensile properties at 20—950℃ and creep rupture properties at 700-900℃ in a Ni3Al-Fe based alloy after high temperature deformation have been studied.Theresults show the microstructure of the alloy is composed of γ′-and β-phases.The grain sizeand yield strength of the alloy is stable when the temperature≤600℃,and it is ductile athigh temperature.The creep of the alloy at 700—900℃ is controlled by the climbing of dislo-cations,and the activation energy for creep is 439 KJ/mol with a stress exponent of 4.

IN SITU GRADIENT DOUBLE-LAYER COMPOSITES OF Al-Fe ALLOY BY CENTRIFUGAL CASTING

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NUCLEATION BEHAVIOR OF Al_8Fe_4Nd PHASE IN RAPIDLY SOLIDIFIED Al-Fe-V-Si-Nd ALLOY

The microstructure of Al-Fe- V-Si-Nd alloy prepared by rapid solidification (RS) pro-cessing was studied by X-ray diffraction (XRD), transmission electron microscopy(TEM) and high resolution electron microscopy (HREM). The phase selection of thealloy during solidification and the nucleation behavior of Al8Fe4Nd phase were ana-lyzed witinin the framework of time-dependent nucleation theory. The incubation timefor Al8Fe4Nd phase was found shorter and the nucleation rate higher than those ofα-Al. The results indicate the nucleation of Al8Fe4Nd phase is heterogeneous and thedispersoids of Al8Fe4Nd form as primary particles from the liquid, which is consistentwith experimental observation.

Abnormal mechanical property evolution induced by heat treatment for a semi-solid forming hypereutectic Al-Fe base alloy

In the present study, Al-5.5Fe-4Cu-2Zn-0.4Mg-0.5Mn al oy samples were prepared by electromagnetic stirring and semi-solid forming processing, and then the effects of T6 and T1 heat treatments on the microstructures and mechanical properties of the semi-solid forming samples were investigated. The results indicate that after semi-solid forming, the mechanical properties of the sample improved significantly compared to that of the merely electromagnetically stirred sample. The grains of semi-solid forming alloy became almost fine equiaxed; big long strip-shaped Al3 Fe phases became short rod-like morphology and distributed uniformly in the matrix. However, the mechanical properties of the T6-treated semi-solid forming sample decreased significantly instead of increasing and, with solution temperature rising, the tensile strength of the al oy decreased further. The results of EDS show that after high temperature solid-solution treatment, the Cu element in the semi-solid forming alloy sample is mainly concentrated at the boundaries of the Al3 Fe phases instead of being dissolved in the matrix. At the same time, the grains of the semi-solid forming sample grew slightly after solid-solution treatment. Therefore, the growth of the grains and the accumulation of Cu element at Al3 Fe phase boundaries during solution treatment of the semi-solid forming alloy were the main reasons for the mechanical properties decreasing after T6 treatment. The mechanical properties of the alloy were improved after T1 heat treatment due to aging strengthening phase being precipitated in the matrix.