Retrogression characteristics of a novel Al-Cu-Li-X alloy

Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The retrogression treatments of aging at 155℃ for 12 h followed by aging at 220 and 240℃ were chosen by determining the peak temperature of δ' precipitation at 230℃ by DSC. The retrogression treatment at a lower temperature of 220℃ causes the precipitation and coarsening of δ' and θ' phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240℃ causes the dissolution and coarsening of δ' and θ' precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T₁, T₂, δ', and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis.     

Influences of 2.5wt% Mn addition on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys

The influences of 2.5wt% Mn addition on the microstructure and mechanical properties of the Cu-11.9wt%Al-3.8wt%Ni shape memory alloy (SMA) were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimeter (DSC). The experimental results show that Mn addition influences considerably the austenite-martensite transformation temperatures and the kind of martensite in the Cu-Al-Ni alloy. The martensitic transformation changes from a mixed xed β₁→β'₁+γ'₁ transformation to a single β₁→β'₁ martensite transformation together with a decrease in transformation temperatures. In addition, the observations reveal that the grain size of the Cu-Al-Ni alloy can be controlled with the addition of 2.5wt% Mn and thus its mechanical properties can be enhanced. The Cu-Al-Ni-Mn alloy exhibits better mechanical properties with the high ultimate compression strength and ductility of 952 MPa and 15%, respectively. These improvements are attributed to a decrease in grain size. However, the hardness decreases from Hv 230 to Hv 140 with the Mn addition.     

钇对银基合金靶材坯料微观组织及性能的影响

采用光学显微镜、SEM、EDS、硬度测试、电阻率测试和耐硫化测试等方法，研究了Y的不同添加量对银基合金靶材坯料显微组织和性能的影响.结果表明:Y添加量较少时，Y主要以固溶体的形式存在，可以起到细化晶粒的作用，而Y添加量过多时，会有第二相析出.当Y添加量为0.1%时材料综合性能最好，此时银基合金靶材坯料的硬度值较高，电阻率较低，耐硫化性能最佳.     

Phase boundary sliding model controlled by diffusionsolution zone in superplastic deformation

With scanning electron microscope (SEM), the surface morphology of phase boundary sliding (PBS) in superplastic deformation (SPD) of Zn-Al alloy and the diffusion behavior of Zn, Al interfaces in their powers' sintering have been investigated. The results show that Zn-Al eutectoid microstructure can be achieved through their powders' sintering, and the diffusion characteristic between Zn and Al is just a demonstration of Kirkendall effect, in which Zn can dissolve into Al whereas A1 can hardly dissolve into Zn. During sintering, a diffusion-solution zone ?′ has formed and subsequently transformed into a eutectoid microstructure in the cooling process. The superplastic deformation mechanism of Zn-Al eutectic alloy is phase boundary sliding which is controlled by the diffusion-solution zone ?′. If the diffusion-solution zone ?′ is unsaturated, it will have much more crystal defects and the combination between ?′ and phase ? is weak, thus the process of phase boundary sliding becomes easily; on the contrary, if the diffusion-solution zone ?′ becomes thick and saturated, the sliding will be difficult.     

稀土对时效-回归-再时效处理的Al-Zn-Mg合金硬度和氢脆的影响

将少量稀土元素添加到Al-Zn-Mg合金中进行时效-回 归-再时效处理.利用扫描电子显微镜和X射线衍射对该合金的显微结构和沉淀相进行了观察和研究. 结果表明, 经过时效-回归-再时效处理后, 稀土Al-Zn-Mg合金的晶粒尺寸减小, 沉淀相MgZn₂增加, 同时, 峰时效硬度和氢脆阻力增强.     

Rapid solidification of undercooled Al-Cu-Si eutectic alloys

Under the conventional solidification condition, a liquid aluminium alloy can be hardly undercooled because of oxidation. In this work, rapid solidification of an undercooled liquid Al_80.4Cu_13.6Si₆ ternary eutectic alloy was realized by the glass fluxing method combined with recycled superheating. The relationship between superheating and undercooling was investigated at a certain cooling rate of the alloy melt. The maximum undercooling is 147 K (0.18T _E). The undercooled ternary eutectic is composed of α(Al) solid solution, (Si) semiconductor and θ(CuAl₂) intermetallic compound. In the (Al+Si+θ) ternary eutectic, (Si) faceted phase grows independently, while (Al) and θ non-faceted phases grow cooperatively in the lamellar mode. When undercooling is small, only (Al) solid solution forms as the leading phase. Once undercooling exceeds 73 K, (Si) phase nucleates firstly and grows as the primary phase. The alloy microstructure consists of primary (Al) dendrite, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic at small undercooling, while at large undercooling primary (Si) block, (Al+θ) pseudobinary eutectic and (Al+Si+θ) ternary eutectic coexist. As undercooling increases, the volume fraction of primary (Al) dendrite decreases and that of primary (Si) block increases. Supported by the National Natural Science Foundation of China (Grant Nos. 50121101, 50395105) and the Doctorate Foundation of Northwestern Polytechnical University (Grant No. CX200419)     

Effect of pre-recovery on microstructure and properties of rolled Al-12.18Zn-3.31Mg-1.43Cu-0.20Zr-0.04Sr aluminum alloy

The independently designed and manufactured ultra-high-strength aluminum alloy Al-12.18 Zn-3.31 Mg-1.43 Cu-0.20 Zr-0.04 Sr was investigated via scanning electron microscopy observations, X-ray diffraction analysis, hardness tests, electrical conductivity tests, tensile tests, intergranular corrosion tests, and exfoliation corrosion tests. The effect of pre-recovery on the microstructure and mechanical properties of this aluminum alloy was also studied. The results show that the pre-recovery heat treatment releases deformation energy, inhibits recrystallization, and decreases the dislocation density. Although the pre-recovery heat treatment has little effect on the hardness, electrical conductivity, and elongation of this aluminum alloy, it can dramatically improve the alloy's tensile strength(the maximum tensile strength increased from 785.0 MPa to 809.2 MPa). Moreover, the tensile properties of this aluminum alloy have a certain degree of isotropy, and the pre-recovery heat treatment does not affect this property. In addition, the rolled aluminum alloy exhibits good corrosion resistance, but the effect of the pre-recovery heat treatment on the alloy's resistance to intergranular and exfoliation corrosion is negligible.     

Ce对耐热铝导体材料铸态组织和性能的影响

采用电阻率测试、硬度测试、金相显微镜和扫描电镜观察等方法,研究添加不同含量稀土Ce对铸态耐热铝导体材料Al-0.15Zr合金的影响。研究结果表明:Ce能净化基体,与杂质相形成金属间化合物,改变杂质相的形态和分布;添加适量的Ce,显著细化了晶粒和枝晶组织,有利于导电性和强度的提高;随着Ce加入量的增大,晶粒细化效果更好;当Ce含量(质量分数)超过0.3%以后,二次枝晶间距继续减小,但晶粒尺寸细化不明显;当Ce含量为0.3%和0.4%时,Al-0.15Zr合金的导电性和强度均达到最大值。     

Electrical conductivity measurement of serpentine at high temperature and pressure

The electrical conductivity of serpentine is measured at 1.0-3. 0 GPa and 300-870℃. The effect of frequencies on electrical conductivity measurement is analyzed. The conduction mechanisms of serpentine before and after dehydration are discussed. Our experimental results show that the electrical conductivity of serpentine increases significantly after dehydration of serpentine, through which highly conductive layers (HCL) can be formed in the Earth's interior.     

基于正交试验对铸造铝合金电导率和抗拉强度影响规律的分析

挑选了铝合金中常用的9种合金元素,根据这些元素对铝合金物理性能和微观组织的影响规律和影响机制进行了分类。通过设计四因素三变量正交试验分析了这些合金元素对Al-7Si合金导电性能和抗拉强度的影响规律,为开发兼具高导电(热)性能和高强度铸造铝合金提供了有价值的工艺参考。通过对比发现,Sr元素能有效将共晶Si相变质为纤维状,这有利于合金电导率的提升;质量分数为0.6%的Fe也能适当提升合金的电导率。Sb元素能有效将共晶Si相变质为细小片状,这有利于合金抗拉强度的提升;质量分数为0.5%的Ni或0.5%的Zn也能适当提升合金的抗拉强度。Sr和Sb同时加入合金中,共晶Si相的变质效果会恶化,并导致粗大片状共晶Si相析出。     

时效状态对Cu-Cr-Zr系合金性能的影响

采用不同时效状态和随后形变热处理工艺制备了Cu-Cr-Zr系合金,采用微观组织观察、硬度和导电率测试等手段研究了不同时效状态对双级时效Cu-Cr-Zr系合金性能的影响.结果表明：欠时效+冷轧+时效工艺和峰时效+冷轧+时效工艺制备的Cu-Cr-Zr-Mg-Si和Cu-Cr-Zr-Ni-Si合金均可获得力学性能和电学性能的优良组合.其中：欠时效+冷轧+时效工艺所制备的合金综合性能更优,但加工热处理过程中性能变化剧烈,材料生产过程中性能均匀性不易控制;峰时效+冷轧+时效工艺制备的合金综合性能极其稳定,易于在生产中控制.不同工艺下的合金性能差异是由析出相与位错的交互作用机制不同造成的.     

Aging behavior and fatigue crack propagation of high Zn-containing Al-Zn-Mg-Cu alloys with zinc variation

In the present work, the influence of two-step aging treatments on hardness, electrical conductivity and mechanical properties of two high Zn-containing Al-Zn-Mg-Cu alloys with zinc content variation was investigated and the detailed T76 aging parameters were proposed. The microstructure of the precipitates were studied by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) and then quantitatively investigated with the aid of an image analysis. The fatigue performances were researched by the fatigue crack propagation (FCP) rate test and fracture morphology was observed with scanning electron microscopy (SEM). The results show that the matrix precipitate size distributions of both alloys had significant difference, so as to fatigue crack propagation rates and fracture appearance. The shear and bypass mechanisms of dislocation-precipitate interactions were employed to explain the difference. Among the shearable precipitates, the proportion of larger size precipitates for the higher zinc content alloy is bigger than that for the lower zinc content alloy. The coarse shearable precipitates hinder the propagation of the fatigue cracks, leading to inferior FCP rate. For both alloys, the shear mechanism possesses the dominant factor, finally causing a preponderance in the FCP resistance for the higher zinc content alloy than the lower one.     

Isotope effect of the stereodynamics in the reactions F+HCl→HF+Cl and F+DCl→DF+Cl

Using a new ground-state ab initio potential energy surface reported by Deskevich et al., the product polarizations in the reactions F+HCl→HF+Cl and F+DCl→DF+Cl were studied by employing the quasi-classical trajectory method. At a collision energy of 10 kcal/mol, the four generalized polarization-dependent differential cross-sections (2π/σ)(dσ₀₀/dω _t ), (2π/σ)(dσ₂₀/dω _t ), (2π/σ)(dσ₂₂₊/dω _t ) and (2π/σ)(dσ₂₁₋/dω _t ) were calculated in the center-of-mass frame. The distribution of the angle between k and j′, P(θ _r ), the distribution of the dihedral angle denoting the k-k′-j′ correlation, P(φ _r ), and the angular distribution of the product rotational vectors in the form of polar plots P(θ _r , φ _r ) were also calculated. The evident influence of isotope substitution on the product polarization is revealed. This effect may result from the different mass factors of the two reactions.     

均匀化处理温度对6082铝合金组织和性能的影响

采用硬度、电导率测试、金相显微镜、X线衍射、扫描电镜、透射电镜和能谱分析技术,研究均匀化温度对合金组织和性能的影响.研究结果表明:铸态合金由α-Al固溶体和非平衡共晶相组成;490～510℃均匀化,Mg2Si相从过饱和固溶体中析出,在510℃以上均匀化,随着温度的升高,Mg2Si又逐步回溶到基体中,560℃均匀化,Mg2Si相和过剩单质Si完全溶解;随着均匀化温度的升高,非平衡析出物鱼骨状共晶形态逐渐消失,针状β-AlMnFeSi溶解、断裂,转变为具有更高(Mn+Fe)/Si比值颗粒状α-Al(MnFe)Si相,析出相在高温均匀化过程中聚集、球化;560℃均匀化,析出物的连续网状结构转变成链状结构,析出物演化为等轴粒状α-Al(MnFe)Si相.均匀化过程中合金中析出弥散α-Al(MnFe)Si相;在490～560℃保温6h均匀化处理,温度升高,合金的硬度和电导率分别升高和降低.     

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature (HPHT) sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, B, and Ti. The thermal conductivity (TC) obtained exhibited as high as 688 W·m-1·K-1, but also as low as 325 W·m-1·K-1. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.     

Directional solidification and physical properties measurements of the zinc-aluminum eutectic alloy

Zn-5wt% Al eutectic alloy was directionally solidified with different growth rates (5.32–250.0 μm/s) at a constant temperature gradient of 8.50 K/mm using a Bridgman-type growth apparatus. The values of eutectic spacing were measured from transverse sections of the samples. The dependences of the eutectic spacing and undercooling on growth rate are determined as λ=9.21V-0.53 and ΔT=0.0245V0.53, respectively. The results obtained in this work were compared with the Jackson-Hunt eutectic theory and the similar experimental results in the literature. Microhardness of directionally solidified samples was also measured by using a microhardness test device. The dependency of the microhardness on growth rate is found as Hv=115.64V0.13. Afterwards, the electrical resistivity (r) of the casting alloy changes from 40×10-9 to 108×10-9 Ω·m with the temperature rising in the range of 300–630 K. The enthalpy of fusion (ΔH) and specific heat (C_p) for the Zn-Al eutectic alloy are calculated to be 113.37 J/g and 0.309 J/(g·K), respectively by means of differential scanning calorimetry (DSC) from heating trace during the transformation from liquid to solid.     

铈和铬对纯铜性能的影响

研究了不同铈和铬的加入量对纯铜的导电率、强度、硬度、耐磨性及显微组织的影响。研究发现,在纯铜中加入适量和铬可以在不影响纯铜的良好导电性的同时,提高其强度、硬度,并可有效的细化组织,净化基体。试验结果表明当铜中铈铈的加入量为0．08％,铬的加入量为0．4％时,具有良好的综合性能。     

Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer, and differential scanning calorimeter (DSC). Experimental results show that bainite, γ_2, and α phase precipitates occur with the aging effect in the alloy. After aging at 300dgC, the bainitic precipitates appear at the early stages of aging, while the precipitates of γ₂ phase are observed for a longer aging time. When the aging temperature increases, the bainite gradually evolves into γ₂ phase and equilibrium α phase (bcc) precipitates from the remaining parent phase. Thus, the bainite, γ₂, and α phases appear, while the martensite phase disappears progressively in the alloy. The bainitic precipitates decrease the reverse transformation temperature while the γ₂ phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase. On the other hand, these precipitations cause an increasing in hardness of the alloy.