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• The cyclic strengthened AA2024 alloy combines excellent strength, elongation, and corrosion resistance. • Cyclic deformation and aging treatment method is applied to modify precipitate distribution in AA2024 alloy. • Discontinuous grain boundary precipitates and minimized precipitate-free zones can be observed. • Enhanced strength and corrosion resistance of AA2024 alloy through cyclic deformation and aging treatment. For the traditional peak-aged (PA) AA2024 alloy, the formation of large S-phase precipitates within the grains, wide precipitate-free zones (PFZs) near the grain boundaries (GBs), and continuous distribution of grain boundary precipitates (GBPs) can be observed. As a result, the PA alloy exhibits relatively high strength but poor corrosion resistance. However, with the application of cyclic plasticity treatment, high-density 1–2 nm clusters form within the matrix, and no PFZs form near GBs. In this study, this treatment yields the optimal balance between strength–elongation characteristics and corrosion resistance. By combining cyclic plasticity and ageing heat treatment with different heating rates, the nanoscale clusters play a crucial role as heterogeneous nucleation sites, resulting in the formation of finer and higher number density of S precipitates within the matrix. Additionally, the presence of these clusters reduces the formation of GBPs and minimizes the width of PFZs. Consequently, compared to the traditional PA sample, this approach achieves a significantly higher yield strength (increased by 46 %) and ultimate tensile strength (increased by 18 %), along with superior corrosion resistance. Although the influence of ageing heat treatment with different rates on mechanical properties is not significant, it notably affects the formation of GBPs and corrosion resistance. Specifically, a slower heating rate leads to an increase in the spacing between adjacent GBPs, resulting in improved corrosion resistance. In summary, cyclic strengthening, as a novel method for alloy strengthening, when combined with ageing heat treatment, modulates the distribution of S precipitates within the matrix and GBs. This optimization maximizes the effects of precipitation strengthening and breaks the inverse relationship between strength and corrosion resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Cu induces a "branched" path for the structural transformation of L1 2 -Al 3 Zr phase. • Cu addition increases the energy barrier for APB activation by ≈ 50 %, increasing the thermal stability of the L1 2 phase. • Cu atoms may preferentially segregate at the Al-Zr layer adjacent to the APB, promoting a transformation to a new phase, termed as Al 4 CuZr. The effect of Cu on the evolution of the Al 3 Zr phase in an Al-Cu-Zr cast alloy during solution treatment at 500 °C has been thoroughly studied by combining atomic resolution high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy and first-principles calculations. The heat treatment initially produces a pure L1 2 -Al 3 Zr microstructure, allowing for about 13 % Cu to be incorporated in the dispersoid. Cu incorporation increases the energy barrier for anti-phase boundary (APB) activation, thus stabilizing the L1 2 structure. Additional heating leads to a Cu-induced "branched" path for the L1 2 structural transformation, with the latter process accelerated once the first APB has been created. Cu atoms may either (i) be repelled by the APBs, promoting the transformation to a Cu-poor D0 23 phase, or (ii) they may segregate at one Al-Zr layer adjacent to the APB, promoting a transformation to a new thermodynamically favored phase, Al 4 CuZr, formed when these segregation layers are periodically arranged. Theoretical studies suggest that the branching of the L1 2 transformation path is linked to the speed at which an APB is created, with Cu attraction triggered by a comparatively slow process. This unexpected transformation behavior of the L1 2 -Al 3 Zr phase opens a new path to understanding, and potentially regulating the Al 3 Zr dispersoid evolution for high temperature applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The thermal deformation behavior of spray formed Al–Zn–Mg–Cu alloy was investigated by the isothermal hot compression tests at the strain rates of 0.001–10 s−1with the temperature range of 350–450 °C. An Arrhenius constitutive equation was established by the corrected strain-stress curves, and then the processing map was constructed based on the 3D instability map and 3D power dissipation map. The influence of strain rate and temperature on both flow stress and dynamic softening has been unveiled. The results show that dynamic recovery (DRV) is the primary softening mechanism and dynamic recrystallization (DRX) is substantively retarded due to the fine dispersed particles uniformly distributed in the spray formed alloy. Continuous dynamic recrystallization (CDRX) is the primary DRX mechanism at a low temperature or high strain rate. DRX grain was observed at the grain boundaries, especially at the triple junctions. The appropriate thermal deformation condition is recommended at the temperature range from 430 °C to 450 °C and strain rates from 0.003 s−1to 0.1 s−1.

The effects of Cu and Sn additions on the precipitation hardening of Al-Mg-Si alloys were systematically studied by performance testing and microscopic characterisation. Sn addition can retard the onset of natural aging (NA), while after long-term NA, the NA hardening is enhanced. Although Cu and Sn can promote the NA hardening, the Cu and Sn combination addition results in NA hardness lower than the individual Cu addition. Compared with Sn, Cu addition is more efficient in promoting the artificial aging hardening of these alloys. Both of the Sn and Cu atoms can incorporate in the interior of the ß'' phase and produce disordered structure. The results are expected to provide new insight for designing new aluminium alloys for automotive application.

The effects of Cu and Sn additions on the precipitation hardening of Al-Mg-Si alloys were systematically studied by performance testing and microscopic characterisation. Sn addition can retard the onset of natural aging (NA), while after long-term NA, the NA hardening is enhanced. Although Cu and Sn can promote the NA hardening, the Cu and Sn combination addition results in NA hardness lower than the individual Cu addition. Compared with Sn, Cu addition is more efficient in promoting the artificial aging hardening of these alloys. Both of the Sn and Cu atoms can incorporate in the interior of the β′′ phase and produce disordered structure. The results are expected to provide new insight for designing new aluminium alloys for automotive application.

The compression creep behavior of 8030 aluminum alloys at intermediate temperature was studied under the deformation temperature of 200∼250 °C and compression stress ranging from 20 to 40 MPa. The apparent stress exponent (na), the true stress exponent (nt) and the activation energy Qcfor creep were na = 3.6, nt = 3 and Qc = 145.5 kJ/mol, respectively, indicating that the dislocation viscous glide controlled by lattice self-diffusion was the dominant creep mechanism of the samples at 200 °C-20 MPa. A creep constitutive equation was introduced with the threshold stress σ0 = 5.1 MPa. The microstructure characterization of selected samples was investigated by transmission electron microscopy (TEM), indicating that the sub-grain contours became ambiguous and the dislocations with long curved morphologies were homogeneously distributed within grain inners after creep for 100h.

ABSTRACTThe effect of Sn or In addition on natural ageing and subsequent artificial ageing of Al–Mg–Si alloys was investigated. In addition not only retarded the natural ageing but also improved the T6 hardness. Although Sn addition retarded the natural ageing as well, precipitation kinetics was delayed. In addition, slightly refined the β′′ phase distribution. But β′′ phase was coarse with addition of Sn. During artificial ageing, the vacancies released from binding complexes promote the formation of β′′. The detrimental effects of Sn on artificial ageing could be attributed to the reduction of the amount of Sn solutes and of available Mg solutes forming β′′.

The effect of Sn or In addition on natural ageing and subsequent artificial ageing of Al–Mg–Si alloys was investigated. In addition not only retarded the natural ageing but also improved the T6 hardness. Although Sn addition retarded the natural ageing as well, precipitation kinetics was delayed. In addition, slightly refined the ß'' phase distribution. But ß'' phase was coarse with addition of Sn. During artificial ageing, the vacancies released from binding complexes promote the formation of ß''. The detrimental effects of Sn on artificial ageing could be attributed to the reduction of the amount of Sn solutes and of available Mg solutes forming ß''.

In this work, two different intermediate annealing processes, single-step annealing (SSA, 530 °C/15 h) and two-step annealing (TSA, 450 °C/5 h + 530 °C/15 h), were used to tailor microstructure before cold-rolling and annealing of the final twin-roll cast Al-Mn foils. The recrystallization behavior and mechanical properties during annealing of severely cold-rolled foils were systematically studied. Our results show that discontinuous recrystallization occurs in SSA-foils during annealing at 150–310 °C, in contrast with continuous recrystallization in TSA-foils. The continuous recrystallization develops much finer grains (∼1.35 μm) in the TSA-foils than those by discontinuous recrystallization in the SSA-foils (∼14.7 μm). The texture components in cold-rolled TSA-foils hardly change (retained rolling-textures) after continuous recrystallization, while those in the cold-rolled SSA-foils mainly transform into a strong cube component {001} 〈100〉 after discontinuous recrystallization. Finally, a maximized elongation to fracture of ∼23.9% was achieved in the TSA-foil, much higher than that of the SSA-counterparts, ∼8.3%. The relationships between the microstructure and mechanical properties were discussed. [ABSTRACT FROM AUTHOR]

Gradient nanograin (GNG) metals possess outstanding resistance to sliding friction and wear. The tribolayer plays a major role in the wear performance of metals. However, the current understanding of the tribolayer in GNG metals is still limited. In particular, some GNG metals show low wear resistance under high contact stress. Here, we investigate the wear behavior of coarse grain (CG) and GNG Ti-6Al-4V alloys and its impact on the wear resistance by sliding contact experiments in combination with finite element modeling. We have found wear-induced the oxidation tribolayer with amorphous structures in GNG Ti-6Al-4V alloy for the first and its impact on wear behavior. It is found that the wear damage mainly occurs in the oxidation tribolayer with amorphous structures, which can generate micro-cracks in Ti-6Al-4V alloy. The wear behavior, including wear resistance, wear micro-cracks, and subsurface structural transformations, is stress-dependent, which can be divided into two distinct regimes-elastic and plastic. Coarse grains (CGs) can form the oxidation tribolayer with amorphous structures in elastic and plastic regimes. Compared to CGs, gradient nanograins (GNGs) can suppress the formation of the oxidation tribolayer with amorphous structures and have higher wear resistance in elastic regime, while GNGs form the oxidation tribolayer with amorphous structures more quickly and have lower wear resistance in plastic regime. This work forges the links between stress-dependent subsurface structural transformations and wear resistance for GNGs, and may provide guidance for the wear application of GNG metals.

Self-organization of membrane-embedded peptides and proteins causes the formation of lipid mesostructures in the membranes. One example is purple membranes (PM), which consist of lipids and bacteriorhodopsin (BR) as the only protein component. The BRs form a hexagonal crystalline lattice. A complementary structure is formed by the lipids. Employing BR and PM as an example, we report a method where major parts of the mesoscopic self-assembled protein structures can be extracted from the lipid bilayer membrane. A complementary lipid nanostructure remains on the substrate. To remove such a large number of thiolated proteins simultaneously by applying a mechanical force, they are first reacted at physiological conditions with gold nanoparticles, and then a thin gold film is sputtered onto them that fuses with the gold nanoparticles forming a uniform layer, which finally can be lifted off. In this step, all of the previously gold-labeled proteins are pulled out of the membrane simultaneously. A stable lipid nanostructure is obtained on the mica substrate. Its stability is due to either binding of the lipids to the substrate through ionic bonds or to enough residual proteins to stabilize the lipid nanostructure against reorganization. This method may be applied easily and efficiently wherever thiolated proteins or peptides are employed as self-assembling and structure-inducing units in lipid membranes.

The oxygen-deficient SrFeO2.74 phase of quenched samples is located within the miscibility gap of the SrFeO3–δ perovskite system, and exhibits a manifold vacancy ordering pattern at room temperature. We have studied the complex ordering by high-resolution electron microscopy, and by electron and X-ray diffraction. New principal superlattice structures have been identified by electron diffraction which can be of relevance for the electronic and magnetic properties of this respective perovskite system. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Based on the theory of probability, the probabilistic analysis of slope stability is conducted. Equations for the estimation of slope failure probability are first derived using direct integrations. However, the complexity of the integrations is formidable. In order to overcome the limitation of the direct integration, the first-order second-moment approximation of the slope failure probability is employed for more complex slope stability problems. The study indicates that the distributions of parameter values play a significant role in slope stability, which can not be disclosed by the conventional methods of stability analysis. Greater dispersiveness of the parameter values will lead to a different probability of failure, although the factor of safety estimated by conventional methods remains the same if the mean values of the parameters are unchanged. By taking consideration of the distributions of the parameters, the probability model can provide more reliable designs of rock slopes.

The deterministic description of rock excavation stability with a safety factor is frequently insufficient and, sometimes, misleading. The applications of the probabilistic analysis to determine the likelihood of a rock excavation failure have been proposed by many researchers. The probabilistic analysis will lead to a better understanding of excavation stability and provide more complete information.

Complex fluorides KCoF3and KNiF3with perovskite structures were solvothermally synthesized at 120–180 °C and characterized by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy.

The complex fluorides of AZnF3(A = Na, K), which are isostructural with perovskite phases were obtained by the method of hydrothermal synthesis at 160–220 °C. Compared with traditional high-temperature solid-state method, the products were pure and contained lower amount of oxygen.

Anodic activation of aluminum alloys in chloride solution, as a result of segregation of the trace element Pb by heat-treatment, has recently been investigated extensively on commercial and model binary alloys. Certain commercial alloys are activated by heat-treatment at temperatures as low as 350°C, whereas others have to be heated to significantly higher temperatures (600°C)to obtain a similar effect. Activation by annealing at low temperature has often been attributed to the presence of the alloying element Mg. This work investigates the effect of Mg on the segregation of Pb in a ternary Al–Mg–Pb model alloy by use of electron-optical and electrochemical characterization. The presence of Mg in the alloy-enhanced Pb segregation to the surface at 450°C, which in turn resulted in a more activated surface in relation to the binary Al–Pb alloy. Magnesium segregated to the surface was oxidized as spinel MgAl2O4. By annealing at 600°C, both alloys exhibited increased activation since Pb segregated as both metallic particles and a continuous nanofilm at the oxide–metal interface. However, the Al–Pb alloy became more active than the Al–Mg–Pb alloy. This was attributed to the passivating effect of the spinel on alloy Al–Mg–Pb.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.