微量稀土对高压阳极电容铝箔织构演变的影响

采用晶体取向分布函数方法（ODF）和X射线衍射测定板面晶面衍射强度研究和分析了在高纯铝加入微量稀土（Y）对箔材织构演变的影响。研究结果表明：添加微量稀土，能改变高纯铝箔中变形织构组分的相对强度，随稀土含量增加，黄铜取向密度增加，S织构组分减少，成品退火箔材中立方织构含量随稀土含量增加就相应减少。当稀土含量为0.0030%时，成品退火箔材中立方织构取向密度最大。其作用机理是稀土元素Y化学活性强，能与铁等微量杂质元素形成一系列化合物，析出后可净化基体，降低基体中铁等杂质的浓度，消除杂质元素对高纯铝箔中立方织构形成的不利影响。     

Behaviour of hydrogen impurity in aluminium alloys during anodizing

The present study examines the behaviour of hydrogen impurity in an Al-6.5 at.% W alloy during anodizing, using elastic recoil detection and nuclear reaction analyses. Increased concentrations of hydrogen are found near the alloy/anodic film interface, amounting to ∼2×10¹⁵ H atoms cm⁻² for the particular alloy, containing 0.1-0.3 at.% hydrogen in the bulk regions, and conditions of anodizing. The enrichment arises from hydrogen in the alloy (i) diffusing to the interface, which acts as a trap, or (ii) accumulating at the interface, due to the growth of the anodic film, or a combination of both processes. Diffusion is consistent with the known mobility of hydrogen in aluminium near ambient temperature. Further, accumulation, and subsequent oxidation, of hydrogen are expected based on the general behaviour of alloying elements in anodized aluminium. The anodic films contained ∼0.1-0.3 at.% hydrogen, originating from either the electrolyte or the alloy.     

铝合金热变形组织演化的模拟

采用基于位错攀移及位错间交互作用的多元位错模型,对Al-Mg-Si(6005)合金热变形过程中亚晶内位错密度,亚晶界位错密度,可运位错位错密度及总的位错密度的演化进行了计算机模拟,并由此对Al-Mg-Si合金热压缩过程中的流变应力演化进行了预报,模拟结果和试验结果吻合较好,采用试验研究的方法建立了亚晶尺寸随变形条件演化的半经验关系模型,为铝合金热变形组织演化的预测和控制提供了实用模型。     

Molecular plating of cobalt and neodymium on thin aluminium foils

The electrodeposition via the method of molecular plating (MP) has been specified so that chemical reactions with common backing materials become negligible. The water content in the organic electrolyte is clearly defined and any addition of acid is avoided. This MP-technique is tested by deposition of cobalt and neodymium on aluminium foils of thickness 2.5 and 5 μm. Quantitative results are presented for thin Co-layers and both thin and thick Nd-layers.     

Behaviour of aluminium foam under uniaxial compression

Abstract

The deformation behaviour of different types of closed cell aluminium foam (Alulight, Alporas) was studied. Compression tests indicate that inhomogeneities in the density distribution might be the key factor in determining the mechanical behaviour of foams. Strengthening and softening of the foam can be related to the formation of deformation bands. Depending on the composition and the microstructure of the cell wall material, cells undergo either ductile or brittle collapse. A three dimensional finite element analysis, which has the capability to simulate the initial deformation of foam samples, is presented. Continuum mechanics methods are used to describe the behaviour of foam. Each foam sample is divided into subregions, according to their density distribution. Scaling laws are used to simulate the mechanical properties of the subregions. Experimental data are compared with results of the presented model. Very good agreement between experiments and modelling was found for the rather inhomogeneous Alulight material.     

Microstructural evolution during simulated OLAC processing of a low-carbon microalloyed steel

The microstructural evolution during simulated on-line accelerated cooling (OLAC) of a commercial Grade 80 pipe steel was studied using a quench deformation dilatometer. The transformed matrix microstructure contains various amounts of polygonal ferrite, granular bainite and acicular ferrite, depending mainly on the accelerated-cooling interrupt temperature. The final microstructure is predicted well by drawing the OLAC schedule on the appropriate CCT diagram. Three distinct groups of precipitates are found in the final microstructure, which form during reheat, austenite deformation, and cooling, respectively. The distribution and composition of the precipitates varies widely with steel composition and processing schedule. The microstructure of industrially processed plate agrees well with that of corresponding laboratory simulations.     

The effect of aluminium depletion on the oxidation behaviour of FeCrAl foils

Abstract

In thin FeCrAl foils, the formation of a chromia layer within or underneath the alumina layer has been observed after consumption of the aluminium from the alloy. For Aluchrom I SE, the growth law of the alumina-forming step has been evaluated and an activation energy for oxygen diffusion of 383 ± 36 kJ mol^?1 has been determined. For the growth mechanism of the chromia layer, three models are introduced and discussed. In agreement with a model proposed by H. E. Evans, the measurements of the aluminium content resulted in complete aluminium consumption before the beginning of chromia formation. Because of strong deformation of the thin samples during oxidation, a model is proposed to calculate the alloy thickness based on the amount of aluminium consumption. From a comparison of these calculated values with the measured thicknesses, the elongation of the sample due to creep processes could be determined.     

铝电解电容器用电子铝箔的性能分析与比较

利用原子吸收光谱仪(AAS)、电子扫描电镜(SEM)、电子背散射技术(EBSD)、电化学工作站等方法对不同厂家生产的铝电解电容器用电子铝箔各方面的性能进行比较和分析。结果表明,国产铝箔在微量元素设计和杂质控制,立方织构控制方面已达到国外同类产品的先进技术水平,但表面加工质量,氧化层均一性和微量元素的分布控制方面与国外存在差距。     

Influence of tin and bismuth on machinability of lead free 6000 series aluminium alloys

Abstract

The present paper presents the microstructural characteristics of an extruded AA6012A-T6 (AlMgSiBiSn) alloy and the microstructural changes occurring during turning operations, analysing the mechanism involved in chip breaking. An experimental investigation has been conducted to determine the effects of different cutting speed and feedrate on the machinability of the alloy. The machinability of the AA6012A-T6 alloy, where Pb is substituted by Bi and Sn, has then been compared to the standard AA6012-T6 (AlMgSiPb) and AA6082-T6 (AlSiMg) alloys. The results indicate that the extensive plastic deformation induces a preferred orientation of the grain structure and secondary phases along the shear plane, and a local increase in the alloy temperature. Low melting point compounds, such as the Sn and Bi bearing particles, transform into a soft or liquid state, changing their initial compact shape to assume a needle-like morphology. The β-Mg₂Si and α-Al(FeMn)Si particles are not influenced by the working temperature and keep their initial shape. The AA6082-T6 alloy shows a very poor machinability, with long and continuous strips, while the AA6012A-T6 alloy reveals a good chip formation with small and discontinuous C shaped chips, similar to the AA6012-T6 (AlMgSiPb) alloy. In particular, a feedrate higher than 0·2 mm rev^?1 provides short and suitable chips, independently of cutting speed.     

Behaviour of vacancies during oxidation

Abstract

The behaviour of point defects during oxidation has been re-examined in terms of the process of vacancy injection, the oxide-induced stress, and the oxygen-carbon gas reaction. In zinc and magnesium, the growth of dislocation loops as a function of oxygen pressure for specimens of different orientation is incompatible with the concept of oxidation-induced stress, but is consistent with vacancy injection. In nickel containing carbon, the amount of voiding on oxidation is prolific and is associated with the production of CO₂. However, the measurement of oxide-induced tensile stress and the metallographic examination of oxidized single crystals both support a process of vacancy injection rather than vacancy generation by oxide-induced stress. In decarburized nickel, the oxidation rate increases dramatically compared with carbon-containing nickel, because the vacancies produced by oxidation are not required to relieve the stresses set up by the gas pressure arising from the carbon-oxygen gas reaction and are annihilated at the oxide/metal interface giving rise to spalling. In the absence of an oxide film, the source of vacancies is dislocations. The role of induced stress, whatever its source, is simply to aid or inhibit the precipitation of vacancies as appropriate.

MST/180     

高温合金超薄板循环塑性本构模型适用性研究

高温合金具有优良的综合性能,是航空发动机高性能构件的首选材料.由于高温合金带材屈服强度高、壁厚超薄、回弹明显、构件成形精度难以控制,因此研究现有循环本构模型对于高温合金带材变形预测的适用性具有重要意义.基于循环剪切实验,研究了不同循环塑性本构模型(Armstrong-Frederick(A-F)模型、Yoshida-Uemori(Y-U)模型和the anisotropic nonlinear kinematic(ANK)模型)对高温合金超薄带材循环塑性变形响应的表征效果.同时,通过U形弯实验和有限元仿真结果的对比,分析了不同屈服准则(Hill48,Barlat89和YLD2000-2d)结合不同循环塑性模型对于回弹预测的影响.结果表明,采用Y-U模型对高温合金超薄板循环塑性变形行为的表征能力最好,A-F和ANK模型次之.采用Y-U模型对回弹的预测精度高于各向同性模型和A-F模型,而屈服准则对回弹预测精度的影响不大,采用基于Hill48和YLD2000-2d屈服准则的Y-U模型,回弹预测误差可以控制在5％以内.     

Mathematical model of deformation and microstructural evolution during hot rolling of aluminium alloy 5083

Abstract

A mathematical model to predict the through thickness temperature, strain and strain rate distributions during hot rolling and the subsequent microstructure evolution was developed using the commercial finite element package ABAQUS. Microstructure evolution predictions included the amount of recrystallisation through the thickness of the sheet based on its thermomechanical history during rolling and thermal history after rolling. The equations used to predict the microstructure evolution were based on semiempirical relationships found in the literature for a 5083 aluminium alloy. Validation of the model predictions was done using comprehensive experimental measurements which were conducted using the Corus research multimill, a pilot scale experimental rolling facility, in Ijmuiden, The Netherlands. The results indicate that the through thickness temperature and strain distribution predictions for the rolling operation are reasonable. Hence, the boundary conditions used in the finite element model adequately represent the interface heat transfer and friction conditions. Microstructure predictions using the literature based equations significantly underestimate the amount of recrystallisation occurring in the sheet. A sensitivity analysis indicates that the recrystallisation kinetics are extremely sensitive to the fitting parameters used in the microstructure equation, and that the gradient in the recrystallisation kinetics is the result of the temperature gradient experienced by the specimen during deformation.