Effect of rare earth samarium addition on the kinetics of precipitation in AI-Cu-Mn casting alloy

The mechanical properties of Al-Cu-Mn casting alloy mainly depend on the morphology, distribution, size, and number ofθ′（Al2Cu） precipitates. In this study, we have analyzed the effect of rare earth samarium （Sm） addition on the kinetics of precipitation in the Al-Cu-Mn casting alloy by using differential scanning calorimetry （DSC） and high-resolution transmission electron microscopy. Thermal ef-fect peaks that are attributed to the formation and the dissolution of Guinier-Preston （GP） zone andθ′phase were identified from the DSC curves. The activation energy ofθ′formation was calculated by using both the Kissinger method and the analytical model, and the corre-sponding results were compared. Results suggest that the activation energy ofθ′formation in Al-Cu-Mn alloy is dramatically higher than that in Al-Cu-Mn-Sm alloy. Accordingly, it is concluded that the addition of rare earth Sm decreases the activation energy ofθ′formation and promotes the formation ofθ′precipitates.     

调整农业种植结构对农业节水的影响

邢台市主要农作物为冬小麦-夏玉米,种植冬小麦-夏玉米粮食作物,在平水年只有8月、9月份的降水能满足作物生长需水量,其他10个月缺水368.4mm。在平水年,种植棉花一年中有5个月缺水,缺水量为79.6mm,由于棉花生长期需水量与降水季节同步,缺水量较小。利用邢台市2001~2012年棉花种植面积资料,与种植粮食作物进行对比分析,平均每年可节约灌溉用水3.161 2亿m3。     

张家口市年降水量的加权马尔科夫链预测

根据张家口市1970~2010年的年降水量系列对2011年、2012年的年降水量状态进行加权马尔科夫链预测,再结合模糊集理论中的级别特征值对2011年、2012年的年降水量数值进行预测,与实际年降水量相比,相对误差仅为5%和-3.5%,预测成果合理可靠,结果较为令人满意。     

Preparation of fibrous nickel oxide particles

1　INTRODUCTIONThenickeloxide (abbreviatedasNiOthereafter)isaversatilematerialwhichhasbeenfoundmanyap plicationsinindustrialfields .Itisusedasthekeymaterialinmanufactureofbatteryelectrode ,cata lyst,thermalsensitiveelement ,gassensitiveele ment,functionalceramics ,glass ,electroniccompo nentsandsoon[18] .At present,theapproachesavailableforultrafineNiOparticlesproductionincludecarbonylmethod ,laserchemicalmethod ,pyrolysisbymicrowave ,sol gelmethod ,pyrolysisbyultrason ic ,precipitation …     

Preparation of Y2O3：Eu^3＋ phosphor by molten salt assisted method

A kind of fine and quasi-spherical Y2O3：Eu^3＋ phosphor was prepared by firing a preparative precursor at 1 200 ℃ for 2 h with the molten salts of Na2CO3, S and NaCl. The precursor was obtained by homogeneous precipitation of yttrium and europium with oxalic acid when using EDTA, citric acid or starch as complexant. The structure and morphology of the phosphors were characterized by XRD and SEM, respectively. The influence of complexing environment, firing temperature and molten salts on formation of the phosphor Y2O3：Eu^3＋ was discussed. The result show that the prepared Y2O3：Eu^3＋ phosphor is of quasi-spherical structure with size of 2-3 μm. Its luminescent intensity is 30% higher than that of the same phosphor prepared by the same procedure but without molten salts, and is 5% higher than that of commercial Y2O3：Eu^3＋ red phosphor.     

Numerical Simulation of Internal Oxidation of Steels during Annealing Treatments

This paper presents a new model for simultaneous diffusion and precipitation of chemical elements in metallic matrices, a scheme for its numerical solution, and several applications to problems of internal oxidation. The model basically stands as an extension of the classical Wagner model for internal oxidation of steels, but is more much general in that it allows for an arbitrary number of diffusing chemical elements, an arbitrary number of precipitate phases with arbitrary compositions, dependence of diffusion coefficients and solubility products upon (time-dependent) temperature, etc., thus allowing for a much broader range of applications. As a counterpart, it is generally impossible to solve the complex, non-linear equations of the model analytically, but this can be done numerically. The simple but efficient numerical scheme proposed is based on explicit 1D finite differences. Experience has shown that this scheme, in spite of its rusticity and the restrictions it imposes on the time-step, is more efficient than more elaborate strategies based on the finite-element method. The applications presented are concerned with internal oxidation of steels during annealing processes. The model and associated numerical scheme allow for evaluation of the amounts of the various oxide precipitates in the external layer of the sheet. This opens the way, through numerical parametric studies of the influence of the process parameters and the chemical composition, to the improvement of existing treatments and the development of new steel grades.     

Dry and clean age hardening of aluminum alloys by high-pressure gas quenching

When precipitation-hardenable aluminum parts are water quenched, distortion occurs due to thermal stresses. Thereby, a costly reworking is necessary, and for this reason polymer quenchants are often used to reduce distortion, with the disadvantage that the quenched parts have to be cleaned after quenching. In opposition to liquid quenchants, gas quenching may decrease distortion due to the better temperature uniformity during quenching. Furthermore, cleaning of the quenched parts can be avoided because it is a dry process. For this purpose, a heat-treating process was evaluated that included a high-pressure gasquenching step. Gas quenching was applied to different aluminum alloys (i.e., 2024, 6013, 7075, and A357.0), and tensile tests have been carried out to determine the mechanical properties after solution annealing, gas quenching, and aging. Besides high-pressure gas quenching, alloy 2024 was quenched at ambient pressure in a gas nozzle field. The high velocity at the gas outlet leads to an accelerated cooling of the aluminum alloy in this case. Aluminum castings and forgings can be classified as an interesting field of application of these quenching methods due to their near-net shape before the heat treatment. Cost savings would be possible due to the reduced distortion, and therefore, less reworking after the precipitation hardening.     

V、N、Nb微合金化对薄板坯连轧带钢组织和性能的影响

在试验室模拟薄板坯连铸连轧过程，板坯均热后被轧制到7mm厚并通过控冷来模拟辊道冷却和带钢的缓慢卷取过程。本文选用低碳钢，研究了V、N、Nb微合金化对其组织和性能的影响。通过试验证明在V-N钢中加入Nb对钢的强化机制有较大影响，使V-N-Nb钢中的析出强化增大，这表明V-N-Nb微合金化可充分地发挥微合金元素在钢中的析出强化作用，析出强化对屈服强度的贡献比V-N微合金化提高17MPa。     

FV520(B)钢时效组织和力学性能分析

通过透射电镜、电子拉伸、示波冲击试验,分析了马氏体沉淀硬化不锈钢FV520(B)850℃油淬后分别在560、600和630℃时效后的组织和力学性能。结果表明,淬火态FV520(B)钢560℃和600℃时效处理后,组织均为过时效马氏体+残余奥氏体,但细微组织有较大的差别,630℃时效处理后,组织为过时效马氏体+马氏体+ 残余奥氏体;560℃时效后强度最高;三种时效温度下,FV520(B)均具有较高的冲击韧度,600℃时效后冲击韧度最高;时效温度对FY520(B)冲击韧度的影响主要决定于其对塑性变形功(Apl)的影响。     

FV520(B)钢时效组织和力学性能分析

通过透射电镜、电子拉伸、示波冲击试验，分析了马氏体沉淀硬化不锈钢FV520（B）850℃油淬后分别在560、600和630℃时效后的组织和力学性能。结果表明，淬火态FV520（B）钢560℃和600℃时效处理后，组织均为过时效马氏体＋残余奥氏体，但细微组织有较大的差别，630℃时效处理后，组织为过时效马氏体＋马氏体＋残余奥氏体；560℃时效后强度最高；三种时效温度下，FV520（B）均具有较高的冲击韧度，600℃时效后冲击韧度最高；时效温度对FV520（B）冲击韧度的影响主要决定于其对塑性变形功（Ad）的影响。