Effect of precipitates on plastic anisotropy for polycrystalline aluminum alloys

The effects of crystallographic texture and precipitate distribution on macroscopic anisotropy in aluminum alloys were investigated. In order to simultaneously consider the effects of crystallographic texture and precipitate distribution on macroscopic anisotropy, predictions of plastic properties were carried out using an anisotropic yield function based on the material texture and a combined isotropic-kinematic hardening rule. The input to the model was a single stress-strain curve, the crystallographic texture, and the precipitate volume fraction, shape, and habit planes. It was shown that the kinematic hardening rule, which expresses a translation of the yield surface in stress space, was a function of all the parameters describing the precipitate distribution. The model was applied to the case of an extruded and recrystallized binary Al-3 wt pct Cu alloy deformed in uniaxial compression in different directions. Excellent agreement was observed between the experimental and predicted yield stress anisotropy and the specimen cross section shape anisotropy. Gaussian distributions of grain orientations around ideal texture components typical of aluminum alloys were generated using computer simulations. These textures were combined with the isotropic-kinematic hardening rule determined for the Al-3 wt pct Cu binary alloy to theoretically assess the influence of precipitates on the r-value (the width-to-thickness plastic strain ratio in uniaxial tension) and yield stress anisotropy for aluminum sheets. It was shown that, for these textures, the precipitate distribution had the effect of reducing plastic anisotropy, in agreement with the trends generally observed in practice.     

A lattice parameter study of the precipitates in Al-rich Al-Ag-Zn alloys

Precipitation of the metastable and equilibrium phases has been studied by X-ray diffraction in ternary aluminum rich Al-Ag-Zn alloys. The precipitation sequence was found to be GP zones → ∈ → ∈ Lattice mismatch between the GP zones, ∈, and ∈ phases was found to depend upon the solute content of the alloy. The lattice mismatch between the metastable precipitates and the matrix could be altered by alloying or aging at 150°C. Formerly Lecturer at the University of Manchester, Manchester, England is deceased     

Measurement of the solubility of germanium in aluminum utilizing MeV He+ backscattering

The solubility of germanium in thin (1000 to 6000Å) aluminum films has been measured over the temperature range 120° to 390°C using the technique of MeV He⁺ backscattering. The results are in general agreement with previous measurements. The technique is described and its advantages and limitations for measurements of this type are discussed.     

A rutherford backscattering study of precipitation phenomena in dilute alloys of Nb-H and Nb-D

We have measured, by the technique of channeling and Rutherford backscattering of 1 MeV He ions, the terminal solid solubility of hydrogen in niobium and of deuterium in niobium over the concentration range of 0.24–3.45 at.% and temperature range of 161–249 K. These measurements are made possible by the sensitivity of the He beam to the lattice disorder accompanying precipitation of Nb-H and Nb-D during the α → α + β phase change. The use of ultra-pure single crystals, electrolytically charged with hydrogen or deuterium resulted in terminal solid solubility values slightly higher than those previously reported. We have related the change in backscattered signal to a combination of mismatch of the hydride in the Nb lattice, incoherent precipitates and emitted prismatic dislocations. Thermal cycling has allowed us to compensate for a supercooling effect and has shown the effect of stress in the system on the temperature of precipitation. The technique is shown to be more sensitive than those previously employed in this kind of investigation.     

酸溶铝含量对取向硅钢常化抑制剂析出的影响

以工业0.27 mm规格高磁感取向硅钢为研究对象,研究了酸溶铝(Als)含量对常化板析出物析出行为的影响.结果表明:常化板中的析岀物主要是AlN与MnS和AlN的复合析出物,随着Als含量的升高,析出物数量增加,但析出物平均尺寸变化不大.常化板中粗大的析出物大多是复合析出物,且多是以MnS为核心,AlN在MnS表面析出,而常化板中细小的析出物多为单一的析出物.常化冷却阶段,由于过饱和的Al和N在珠光体区域附近更多地析出,常化板珠光体区域附近存在较多细小的AlN粒子.     

A calorimetric study of precipitation in aluminum alloy 2219

Precipitate microstructures in aluminum alloy 2219 were characterized using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC signatures of individual precipitate phases were established by comparing the DSC and TEM results from samples that had been aged such that only one precipitate phase was present. These signatures were then used to analyze the commercial tempers. It was found that DSC could readily distinguish between the T3, T4, T6, T8 and O tempers but could not distinguish amongst T81, T851 and T87. Small amounts of plastic deformation between solution treatment and aging had a significant effect on the thermograms. Aging experiments at 130 and 190 °C showed that the aging sequence and DSC response of this alloy were similar to those of pure Al-Cu when the increased copper content is taken into account. Further aging experiments at temperatures between room temperature and 130 °C showed pronounced changes of the GP zone dissolution peak as a function of aging conditions. These changes were found to be related to the effect of GP zone size on the metastable phase boundary and on the GP zone dissolution kinetics.     

A crystallographic study of massive precipitates in Cu-Zn and Ag-Zn alloys utilizing selected area electron channelling

Selected area electron channelling patterns (SACP's) obtained on a Cambridge Scientific Instruments Stereoscan SEM have been used to study the orientation relationships between grain boundary precipitates of massive a phase and the adjoining β phase grains in Cu-38.0 at. % Zn and Ag-37.8 at. % Zn alloys. Two types of precipitates were studied, those growing into only one β grain (typeA) and those growing into both grains (typeB). The orientation relationship of the typeA precipitates with the β grain into which it was not growing was frequently consistent with a Bain correspondence, but the precipitates never had a Bain correspondence with the grain into which they were growing. The typeB precipitates did not have a Bain correspondence with either β grain. These results demonstrate that although the precipitates studied sometimes exhibit “oriented nucleation”, none of them showed evidence of “oriented growth”. This conclusion is discussed in terms of current atomistic models for massive transformations.     

片状铝粉制备的研究

目前片状铝粉广泛应用于工业涂料、汽车涂料、油墨及化工等行业,其需求量越来越大．国内外生产片状铝粉的方法较多,本文重点介绍了采用湿法球磨工艺制备片状铝粉方面的研究．     

A study of fracture in high purity 7075 aluminum alloys

Ten different alloys based on the 7075 composition were used to study the effect of purity level, dispersoid type, and heat treatment on fracture toughness. Five purity levels ranging from 0.03 to 0.30 wt pct Fe + Si and two dispersoid types were investigated. Each alloy was given two heat treatments: the standard T651 heat treatment or a special thermomechanical treatment (TMT). Fracture toughness was measured using notched round tensile specimens taken from both the longitudinal and long-transverse directions. The notched round tensile test was modified to give the “plastic energy per unit area”. This fracture toughness parameter gave the same ranking for corresponding alloy/heat treatment combinations as the total energy per unit area measured on precracked Charpy specimens. The fracture toughness ranking for the ten alloys was the same in the longitudinal and long-transverse directions. This suggests the elongated distribution of constituent particles in the rolling direction does not change the failure mechanism. Fractographic evidence showed a bimodal distribution of ductile dimple size in all ten alloys. The number of large ductile dimples decreased with increasing purity level while the number of small ductile dimples increased. This is interpreted to mean that the smaller dispersoid and hardening particles become increasingly important in controlling the fracture toughness as the large intermetallic particles are eliminated by increasing the purity of these aluminum alloys. Since thermomechanical processing controls the amount and type of these smaller particles, it is a useful means for increasing fracture toughness in high purity aluminum alloys.     

Evolution of recrystallization and recrystallization texture in continuous-cast AA 3015 aluminum alloy

The evolution of recrystallization and recrystallization texture during annealing after cold rolling of a continuous-cast (CC) AA 3015 aluminum alloy with and without pretreatment was investigated in detail. It was found that the preheat treatment prior to cold rolling significantly affected the recrystallization kinetics, the shape and size of recrystallized grains, and the resulting texture of the CC AA 3015 aluminum alloy. In the case of the alloy without pretreatment, annealing at low temperatures resulted in coarse elongated recrystallized grains and a very strong P texture. As the annealing temperature increased, the size of the recrystallized grains dramatically decreased, the recrystallized grains became equiaxed, and the strength of the P texture decreased. The transition behavior could be attributed to the effect of Zener-particle pinning caused by concurrent precipitation. In contrast, the recrystallization texture of the CC AA 3015 aluminum alloy with pretreatment was characterized by a major cube component and a minor R component, and the annealing temperature did not affect the recrystallization texture. Moreover, concurrent precipitation retarded markedly the recrystallization of the CC AA 3015 aluminum alloy, decreased the Johnson-Mehl-Avrami-Kolmogorov (JMAK) exponent from 2.0 to 0.5, and increased the activation energy for recrystallization from 225 to 539 kJ/mol.     

Dynamic recrystallization during hot deformation of aluminum: A study using processing maps

The hot deformation behavior of aluminum of different purities has been studied in the temperature range of 250 °C to 600 °C and strain-rate range of 10 3 to 102 s’1. On the basis of the flow stress data, the strain-rate sensitivity (m) of the material is evaluated and used for establishing power dissipation maps following the Dynamic Materials Model. These maps depict the variation of the efficiency of power dissipation [η = 2m/(m +1)] with temperature and strain rate. A domain of dynamic recrystallization (DRX) could be identified in these maps. While the strain rate at which the efficiency peak occurred in this domain is 10_-3 s⁻¹ the DRX temperature is purity dependent and is 375 °C for 99.999 pct Al, 450 °C for 99.995 pct Al, 550 °C for 99.94 pct Al, and 600 °C for 99.5 pct Al. The maximum efficiency of power dissipation for DRX in aluminum is about 55 pct. The sigmoidal increase of grain size with temperature in the DRX domain and the decrease in the DRX temperature with increase in the purity of aluminum are very similar to that observed in static recrystallization, although DRX occurred at much higher temperatures.     

A TEM study of microstructural changes during retrogression and reaging in 7075 aluminum

Microstructural changes occurring during retrogression, and during retrogression plus reaging in 7075-T6 aluminum alloy have been investigated by means of transmission electron microscopy, and related to mechanical properties. TEM results indicate that the drop in strength during the initial stage of retrogression was due to the partial dissolution of G.P. zones while the growth of the semi-coherentη ′ was responsible for the rapid recovery of strength. It is suggested that the retrogression and reaging treatment resulted in the increase in volume fraction of G.P. zones and especially η′ precipitates over both the T6 and retrogressed conditions, therefore significantly improving the strength of the alloy.     

Implicit and explicit personality: A test of a channeling hypothesis for aggressive behavior.

D. G. Winter, O. P. John, A. J. Stewart, E. C. Klohnen, and L. E. Duncan (1998) proposed that self-beliefs about personality influence the channels through which people express their implicit motives. On the basis of this hypothesis, the authors predicted that self-beliefs about aggressiveness would influence the channel(s) through which people express their aggressive motive and the justification mechanisms they use to defend expression of this motive. For example, the authors predicted that people who were implicitly prepared to rationalize a desire to harm others would engage in (a) overt aggression if they viewed themselves as aggressive or (b) passive aggression if they viewed themselves as nonaggressive. The implicit aspects of aggressiveness were measured via conditional reasoning (L. R. James et al., 2005). Results based on intramural basketball players supported the channeling hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A calorimetric study of fatigue induced microstructural changes in aluminum alloy 7050

Differential scanning calorimetry (DSC) was used to detect microstructural changes resulting from strain-controlled fatigue of aluminum alloy 7050. Two starting conditions were investigated: a GP zone T6X temper and an overaged T73651. The calorimetric signature of the microstructure was determined for samples that had been cycled either to failure or to preselected percentages of their expected lifetime at various strain amplitudes. Thermodynamic and kinetic analyses of the calorimetric results revealed a pronounced effect of plastic strain during fatigue on the reaction enthalpy and reaction kinetics of the GP zone dissolution peak of T6X, and a lesser effect on theη′ dissolution peak of T73651. No microstructural changes after fatigue to failure in the nominally elastic strain regime were detected by DSC. The calorimetric results were uniform throughout the cross-section of the fatigue specimens. Based upon these results, it is concluded that approximately 75 pct of the GP zones initially present can be affected during low cycle fatigue, and that overaging of the GP zone microstructure does not occur. The results from the T73651 temper show that low cycle fatigue affects this overaged microstructure in a different manner. Reversion or disordering ofη′ does not occur, but some overaging was detected. It is suggested that theη′ precipitate in this alloy is not shearable.     

Evolution of strain-induced microstructure and texture in commercial aluminum sheet under balanced biaxial stretching

The evolution of surface topography and crystallographic texture was investigated under balanced biaxial stretching in sheets of the aluminum alloy 5052-H32. Two different lots of material, with an initial nominal thickness of 1 mm, were tested in the as-received condition. Samples with increasing levels of balanced biaxial strain were deformed using a modified Marciniak in-plane stretching test. In general, the sheet materials were microstructurally and crystallographically anisotropic. Between the two lots, the initial microstructure and mechanical properties were found to be equivalent; however, the sheet texture was appreciably different. This latter variation was observed to have an effect on the additional roughening of the surface subsequent to deformation. For a given lot of material, the surface roughness was found to be proportional to the magnitude of the strain. However, while the roughening rates for the two lots were comparable, the lot having a stronger initial {220} texture component was found to roughen to a higher degree. Corresponding changes in the sheet texture were observed to have two regimes as a function of the strain level. In the first regime, typically, for strains (ɛ) up to 0.05, the orientations were found to rotate quickly away from the initial cube {001}〈100〉 orientation observed in the as-received sheet toward positions along the α fiber. Above a strain level of 0.05, the {220} texture component continued to increase with deformation, but at a decreasing rate up to failure of the sheet. The difference in the grain rotation rates observed did not appear to have an effect on the surface roughening, as the relative change of the crystallographic orientations with increasing plastic strain was similar for both heats of material. Instead, it is believed that localized grain or grain-grouping interactions may play a more important role in the surface roughening process.     

片状铝粉包覆着色的研究

采用正硅酸乙酯（TEOS）在溶胶一凝胶过程中,酞菁蓝颜料与SiO2共沉积包覆的方法制备蓝色铝粉,采用TEM、EDS、XPS及XRD等手段对着色后的铝粉进行分析．结果表明：在本实验条件得到的着色铝粉表面较为光滑平整、包覆致密完整、耐蚀性强;同时具有亲水性、分散性等特点．彩色铝粉的包覆膜层主要由SiO2和酞菁蓝颜料组成,mSiO2／mAl为0．30,m酞菁蓝／mAl为0．29,酞菁蓝颜料在膜层中的含量呈从里到外逐步递减分布．