Dislocation-Induced Precipitation and Its Strengthening of Al–Cu–Li–Mg Alloys with High Mg

Generally, the good combination of pre-deformation and aging can improve the mechanical strength of the Al–Cu–Li–Mg alloys. However, the effects of pre-deformation on competitive precipitation relationship and precipitation strengthening have not been clarified in detail in Al–Cu–Li–Mg alloys with high Mg. In the present study, the effects of pre-deformation level on the microstructure and mechanical properties of an Al–2.95 Cu–1.55 Li–0.57 Mg–0.18 Zr alloy have been investigated. It is found that the introduction of dislocation by 5% pre-deformation can facilitate the precipitation of new successive composite precipitates and T _1 precipitates along the sub-grain boundaries or dislocations and inhibit the precipitation of dispersive GPB zones which is the main precipitates of the alloys without pre-deformation. The introduction of 5% pre-deformation can enhance the mechanical properties considerably. When the pre-deformation level increases from 5 to 15%, the number density of the successive composite precipitates and T _1 precipitates increases, and the aspect ratio of T _1 precipitates decreases. The decrease in T _1 precipitate aspect ratio and the increment of the successive composite precipitates result in the reduction in precipitation strengthening. Therefore, the increase in pre-deformation level from 5 to 15% does not further improve the mechanical properties of the alloys, although the dislocation strengthening increases continuously.     

The structure and the properties of S-phase in AlCuMg alloys

The S-phase is one of the key strengthening precipitate phases in high-strength 2xxx (AlCuMg) aluminum alloys. Nonetheless, the crystal structure of the S-phase remains controversial, and therefore its physical properties are almost unknown. Using atomic-resolution imaging in electron microscopy and first-principles energy calculations, it was confirmed at last that the structure model proposed by Perlitz and Westgren in 1943 is the only right model for well-developed S-phase precipitates. The structure model proposed by Perlitz and Westgren in 1943 is the only right model. Detailed calculations analysis of the S-phase structure reveals that the characteristics of Cu–Mg bonding and Cu–Al bonding in the structure are basically metallic, but with an ionic character due to electron charge transfer between atoms, leading to a large elastic modulus for the S-phase precipitates to strengthen AlCuMg alloys.     

铝及其合金表面处理的研究现状

较系统地阐述了铝及其合金表面处理的研究现状。介绍了以硬质阳极氧化和复合阳极氧化为主的阳极氧化法、稀土转化膜法以及微弧氧化、激光处理和离子注入等方法。     

Modeling of Plate-like Precipitates in Aluminum Alloys—Comparison between Phase Field and Cellular Automaton Methods

This report compares two approaches for simulating microstructure evolution of plate-like precipitates during artificial ageing of aluminum alloys: the phase field and the cellular automaton methods. Although both methods are based on thermodynamics, they handle the kinetics in quite different ways, each with its own advantages and disadvantages. Both methods were applied to the growth of semi-coherent plate-like precipitates in Al-4 wt% Cu. Good agreement is found between the results of these two models, as well as experiments. A combination of these two methods would provide a novel approach that is both physically sound and computationally effective for the application of precipitation modeling.     

Effect of second phase particles on grain refinement during equal-channel angular pressing of an Al-Mg-Mn alloy

The process of grain refinement under severe plastic deformation was examined in an Al-5.4% Mg-0.5% Mn-0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain interval from 1 to 12 at a temperature of ∼300 °C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al₆Mn particles with an average size of ∼25 nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of ∼0.55 μm evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al₆Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization.     

A model to characterize acoustic softening during ultrasonic consolidation

Ultrasonic consolidation (UC) is a solid state bonding process in which thin metal foils are bonded under the influence of ultrasonic vibration and pressure. Large parts can be made by placing foils side by side or by stacking layers to create thicker parts. Thermal and acoustic softening of metals during UC leads to increased plastic deformation and plays an important role in bond formation. In this work, a thermo-mechanical finite element model is developed to quantify the degree of thermal and acoustic softening occurring in Al 1100-0 foils during UC. The model uses experimentally measured temperatures and changes in the foil's geometry during UC to quantify the amount of thermal and acoustic softening. Acoustic softening is shown to reduce the yield stress of Al 1100-0 foils by up to 82%. In addition, thermal softening is found to be relatively minor, typically less than 5% of the total material softening. This method to quantify acoustic softening during UC allows for a better overall understanding of the bonding process and allows several aspects of the UC bonding process to be optimized and improved.     

包铝层对铝合金腐蚀行为的影响

对LC4CS、LY12CZ、LF6M三种铝合金在厦门海域全浸区有、无包铝层的条件下的腐蚀行为及腐蚀数据进行了对比研究。同时,通过自腐蚀电位和电偶电流的测量,对LF6M（包铝）在厦门海域潮差区的反常腐蚀行为进行了分析。     

冷轧压下量对时效6156铝合金组织与性能的影响

采用拉伸试验、金相观察、X射线衍射、扫描电镜及透射电镜等,研究了180 ℃/1 h欠时效+50~80%压下量冷轧+100 ℃/48 h再时效的6156铝合金组织和力学性能。拉伸测试表明,合金抗拉强度、屈服强度和断裂延伸率分别为515~564 MPa、472~551 MPa和5.7~11.1%,获得高强度和良好塑性。微观分析表明,合金强度源于形变强化和析出强化共同作用,并随压下量增加而增大;合金塑性改善源于位错密度下降和析出强化增强;拉伸断口上沿晶与穿晶断裂并存,增大压下量,韧窝变浅、数量增加。     

Thermo-mechanical and oxidation behaviour of high temperature advanced metallic alloys

The main focus of this paper is on materials for radiant burners application. Two advanced metallic alloys, a Ni and Fe-based alloy are studied and compared to a reference ferritic stainless steel. Oxidation kinetics of such alloys at different temperatures are reported. Oxide formation mechanisms are discussed. Furthermore, thermo-mechanical resistance and eventual strengthening mechanism in temperature are studied. Finally, technical and brief tentative economical analysis of different alloys as potential candidates for the fabrication of radiant burners are given.     

An investigation of electrolytic coloring process of anodized aluminum coatings

In this paper specimens of pure aluminum, AA 5083 and AA 6111 anodized under standard conditions were electrolytically colored from acidic tin sulphate solutions at different rms voltages in order to further gain insight to the ac electrolytic coloring process. Electrochemical methods, SEM/EDS, RBS and XRF techniques were used in this study. The tin deposition efficiency increases with the increase of applied rms electrolytic coloring voltage and the purity of aluminum. The classical linear porosity of the film formed on high purity aluminum favors the tin deposition, while the heavily modified film morphology on AA 6111, impedes it. In the case of reanodizing the anodic-cathodic peak currents quickly reach maximum values and they are influenced by the applied rms voltage and the material types. Their ratio approaches unity indicating symmetry and cooperative movement of the ions through the oxide film. The corresponding ratio of faradaic charges is about 0.6, thus the anodic reactions occur in an extent of about 60% of the cathodic ones. However as the electrolytic coloring is going on and the currents decrease reaching a limited value, then these ratios change slightly not only with respect to the time of coloring but also to the material types. Regardless of the reanodizing or dissolution process being operative during the anodic half cycle, the tin deposition proceeds, when formation of new oxide and redistribution of pores take place. In the case of thinning of barrier layer more time is necessary in order to reach the peak currents their maximum values. The symmetry of these currents is considerably disturbed in the case of alloys but not of pure aluminum, while the ratio of faradaic charges is slightly modified. Thus the capacitance of the oxide films of alloys seems to be considerably altered during the barrier layer dissolution process.     

稀土元素在铝合金阳极氧化及其后处理工序中的应用

在铝合金阳极化溶液中加入稀土添加剂,能够提高氧化膜的耐蚀性能;将稀土盐用于铝合金氧化膜的封闭处理,效果也比较理想,因而稀土元素在铝合金表面处理领域中具有良好的应用前景。介绍了国内外善于稀土元素在铝合金阳极氧化及其后处理工序中的应用情况,并结合目前的研究现状,提出了今后研究中需要进一步探讨的问题。     

Fabrication of metal-matrix composites by application of the superplasticity effect

The production of continuous-fiber metal-matrix composites (MMCs) with improved mechanical properties by solid-state consolidation under superplastic conditions was investigated. The finite-element method was used to model MMC consolidation, which was experimentally studied on a sample of boronaluminum composite. It was shown that the deformation properties of a matrix exert considerable influence on metal flow geometry and its strain-stress state. The superplasticity effect provides the straightening of a matrix flow front and the localization of an intense deformation zone. It also facilitates the removal of pores in the final stage of hardening and considerably decreases local stresses on the fiber surface. The features of matrix material flow during consolidation of composites were considered. It was shown that the matrix deformation during composite consolidation takes place in the form of cooperative grain-boundary sliding and intragranular sliding. The mechanism of matrix deformation determines a type of fiber-matrix reaction at the interface, or, alternatively, the type of fiber-matrix interface interaction depends on the intensity of localized deformation in the given area. Identification of the interface structure was performed by acoustic emission.     

铝合金的表面保护层

传统的秀铬酸盐对铝合金进行表面抗蚀处理存在各污染问题,有许多研究工作在努力开发代铬无毒或低毒的表面保护层,其中有化学方法,也有物理方法,本文中对有关研究工作做了概述。     

The influence of precipitation on plastic deformation of Al–Cu–Li alloys

The plastic behaviour of two recently developed Al–Cu–Li alloys with different Cu/Li ratios, AA2198 and AA2196, was studied as a function of precipitation state by tensile tests, strain hardening rate analysis, Bauschinger tests, slip line imaging and atomic scale characterization of precipitate shearing by advanced electron microscopy. For early ageing times where δ′ and/or solute clusters are present, plasticity occurs heterogeneously, the strain hardening rate is high, and the Bauschinger effect is moderate. When T₁ precipitates are present, plasticity becomes more homogeneous, and the strain hardening rate shows a slower decrease compared with other aluminium alloys containing shearable precipitates. In addition, these ageing conditions show a high reversibility of plastic strain, and it is observed that precipitates are sheared only by single steps. The possibility of a specific shearing mechanism of the T₁ phase is discussed in light of these results.     

机械合金化制备具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响

利用X射线衍射仪、扫描电子显微镜和透射电子显微镜研究了机械合金化制备的具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响。结果表明在573、623、673和723 K退火不同时间后,尽管Al-Pb纳米相复合结构合金中组成相的尺寸均在纳米量级,Pb相的平均颗粒尺寸与退火时间之间仍满足三次方定律。Pb相的粗化激活能为84.80 kJ/mol,此值接近于基体Al的晶界自扩散激活能。这表明Pb相的粗化受晶界扩散控制。添加Cu降低了Pb相的粗化速率,这与Cu在Al和Pb相的界面偏聚,降低了Al/Pb的界面能有关。添加Cu后,Pb相的长大激活能增加。     

A macroscale phase-field model for shape memory alloys with non-isothermal effects: Influence of strain rate and environmental conditions on the mechanical response

A Ginzburg-Landau model for the macroscopic behaviour of a shape memory alloy is proposed. The model is essentially one-dimensional, in that we consider the effect of the martensitic phase transition in terms of a uniaxial deformation along a fixed direction and we use a scalar order parameter whose equilibrium values describe the austenitic phase and the two martensitic variants. The model relies on a Ginzburg-Landau free energy defined as a function of macroscopically measurable quantities, and accounts for thermal effects; couplings between the various relevant physical aspects are established based on thermodynamic principles. The theoretical model has been implemented within a finite-element framework and a number of numerical tests are presented which investigate the mechanical behaviour of the model under different conditions; the results obtained are analyzed in relation to experimental evidence available in the literature. In particular, the influence of the strain rate and of the ambient conditions on the response of the model is highlighted.     

Crystallography of duplex AlN–Nb(C,N) precipitates in 0.2% C steel

Crystallographic aspects related to the formation of duplex AlN–Nb(C,N) precipitates in 0.2% C steel have been evaluated by transmission electron microscopy. Nb(C,N) precipitation occurs with a compromise orientation relationship on favorably oriented AlN particles in the microstructure to minimize the barrier to Nb(C,N) nucleation and growth.