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• The precipitation evolution behaviors and mechanical properties of an Al-Cu-Li-Mg alloy under T3- and T4-aged tempers were firstly studied in detail. • The precipitation sequences of different aged samples during natural aging were determined by using HADDF-STEM. • The intrinsic mechanism of the suppressed nucleation and growth of GPI zones, and the inhibition of δ′/GPI zones/δ′ complex precipitates precipitation in the T3 samples was revealed. • The fundmental reasons for the significantly distinct aging-hardening behaviors between T3- and T4-aged samples were clarifed. The precipitation evolution and mechanical properties of a commercial Al-Cu-Li-Mg alloy in natural aging (NA) tempers (T3 and T4) were investigated in detail. It was demonstrated that GPI zones were the predominant precipitate throughout the NA process. In the T3-aged sample, the precipitation sequence was determined: supersaturated solid solution (SSSS) → atom clusters → GPI zones, whereas in the T4-aged sample, it was SSSS → atom clusters → GPI zones → GPI zones + δ′/GPI zones/δ′. For samples without NA, the strength of the T3 sample was 76.0 MPa higher than that in the T4 sample, which was attributed to the pre-deformation-introduced dislocations. During the early stage of NA, GPI zone nucleation was substantially restricted in the T3 sample, resulting in a much lower number density of GPI zones. It retarded the aging response and strength improvement, consequently narrowing the strength difference between T3 and T4 samples. As the NA process progressed, the average diameter of GPI zones in the T4 sample increased to approximately 4.5 nm, accompanied by the formation of δ′/GPI zones/δ′ composite precipitate. However, GPI zone growth and δ′/GPI zones/δ′ composite precipitate formation were significantly inhibited in the T3 sample, as evidenced by its much smaller average diameter of approximately 2.1 nm and the absence of composite precipitates. It inhibited the strength improvement of the T3 sample. Therefore, after a long period (5 months) of NA, the strength of the T4 sample was about 13.0 MPa higher than that of the T3 samples, instead. [Display omitted] [ABSTRACT FROM AUTHOR]

In the field of electrocatalysis, most of the electrodes have the problem of poor mechanical properties, which leads to the electrode can not be used on a large scale. At present, most bulk electrodes are used to study their mechanical properties due to their unique phase composition distribution and facile fabricate methods. But their novel properties in the field of electrocatalysts have not been fully developed. Multi-element bulk electrodes not only diversified the electronic states, but also build complex surface morphology by different dissolution rate between multi-phase distribution. In this paper, we synthesized the FeNiMo bulk electrode for oxygen evolution reaction (OER) with two-phase coexistence of Mo-doped face center cubic phase (FCC) and Mo-rich intermetallic compound (IMC) phase. During cyclic voltammetry activation, the surface reconstruction of Mo-rich IMC phases generated by ion leaching leaves Fe–Ni pore structures with more active area, which enhances OER performance. Meanwhile, the electron states get more diverse on the surface of remaining FCC phases due to Mo doping, which provides more suitable sites for four-step OER process. The FeNiMo electrode shows an ultra-low overpotential of 212 mV and 293.4 mV at a current density of 10 mA cm−2and 100 mA cm−2, respectively. Moreover, it can maintain stability at 100 mA cm−2for up to 72 h. This work provides a strategy for studying the relationship between phase composition and electrochemical performance of alloy bulk electrodes.

The microstructure evolution and the corrosion feature of Al–xCu–yLi–Mg alloys (x:y= 0.44, 1.65 and 4.2) were systematically investigated under the same artificial aging conditions. The relationships between types of precipitates and mechanical performance, as well as electrochemical behaviors, were discussed. Our results show that different types of precipitates can be obtained in alloys with different Cu/Li mass ratios, which significantly influences the mechanical performance of the alloys and substantial corrosion behaviors. Specifically, the analogous corrosion evolution in the aging Al–xCu–yLi–Mg alloys was first ascertained to be derived from the growth mechanism of the precipitates at the grain boundary (GB). Moreover, a small number of GB precipitates can be obtained in the aged alloy with the lowest Cu/Li mass ratio, thereby resulting in the largest intergranular corrosion resistance. A higher proportion of the GB T1phase in the continuous precipitates induces higher corrosion sensitivity in alloy with a high Cu/Li mass ratio.

A deep understanding of explosive sensitivities and their factors is important for safe and reliable applications. However, quantitative prediction of the sensitivities is difficult. Here, reactive molecular dynamics simulation models for high-speed piston impacts on explosive supercells were established. Simulations were also performed to investigate shock-induced reactions of various high-energy explosives. The fraction of reacted explosive molecules in an initial supercell changed linearly with the propagation distance of the shock-wave front. The corresponding slope could be used as a reaction rate for a specific shock-loading velocity. Reaction rates that varied with the shock-loading pressure exhibited two-stage linearities with different slopes. The two inflection points corresponded to the initial and accelerated reactions, which respectively correlated to the thresholds of shock-induced ignition and detonation. Therefore, the ignition and detonation critical pressures could be determined. The sensitivity could then be a quantitative prediction of the critical pressure. The accuracies of the quantitative shock sensitivity predictions were verified by comparing the impact and shock sensitivities of common explosives and the characteristics of anisotropic shock-induced reactions. Molecular dynamics simulations quantitatively predict and rank shock sensitivities by using only crystal structures of the explosives. Overall, this method will enable the design and safe use of explosives.

Nano-sized aluminum (Nano-Al) powders hold promise in enhancing the total energy of explosives and the metal acceleration ability at the same time. However, the near-detonation zone effects of reaction between Nano-Al with detonation products remain unclear. In this study, the overall reaction process of 170 nm Al with RDX explosive and its effect on detonation characteristics, detonation reaction zone, and the metal acceleration ability were comprehensively investigated through a variety of experiments such as the detonation velocity test, detonation pressure test, explosive/window interface velocity test and confined plate push test using high-resolution laser interferometry. Lithium fluoride (LiF), which has an inert behavior during the explosion, was used as a control to compare the contribution of the reaction of aluminum. A thermochemical approach that took into account the reactivity of aluminum and ensuing detonation products was adopted to calculate the additional energy release by afterburn. Combining the numerical simulations based on the calculated afterburn energy and experimental results, the parameters in the detonation equation of state describing the Nano-Al reaction characteristics were calibrated. This study found that when the 170 nm Al content is from 0% to 15%, every 5% increase of aluminum resulted in about a 1.3% decrease in detonation velocity. Manganin pressure gauge measurement showed no significant enhancement in detonation pressure. The detonation reaction time and reaction zone length of RDX/Al/wax/80/15/5 explosive is 64 ns and 0.47 mm, which is respectively 14% and 8% higher than that of RDX/wax/95/5 explosive (57 ns and 0.39 mm). Explosive/window interface velocity curves show that 170 nm Al mainly reacted with the RDX detonation products after the detonation front. For the recording time of about 10 μs throughout the plate push test duration, the maximum plate velocity and plate acceleration time accelerated by RDX/Al/wax/80/15/5 explosive is 12% and 2.9 μs higher than that of RDX/LiF/wax/80/15/5, respectively, indicating that the aluminum reaction energy significantly increased the metal acceleration time and ability of the explosive. Numerical simulations with JWLM explosive equation of state show that when the detonation products expanded to 2 times the initial volume, over 80% of the aluminum had reacted, implying very high reactivity. These results are significant in attaining a clear understanding of the reaction mechanism of Nano-Al in the development of aluminized explosives.

Impact flash occurs when objects collide at supersonic speeds and can be used for real-time damage assessment when weapons rely on kinetic energy to destroy targets. However, the mechanism of impact flash remains unclear. A series of impact flash experiments of flat-head long-rod projectiles impacting thin target plates were performed with a two-stage light gas gun. The impact flash spectra for 6061 aluminum at 1.3–3.2 km/s collision speeds were recorded with a high-speed camera, a photoelectric sensor, and a time-resolved spectrometer. The intensity of the impact flash exhibited a pulse characteristic with time. The intensity (I) increased with impact velocity (V0) according to I∝V0n, where n = 4.41 for V0 > 2 km/s. However, for V0 < 2 km/s, n = 2.21, and the intense flash duration is an order of magnitude less than that of higher V0. When V0 > 2 km/s, a continuous spectrum (thermal radiation background) was observed and increased in intensity with V0. However, for V0 < 2 km/s, only atomic line spectra were detected. There was no aluminum spectral lines for V0 < 2 km/s, which indicated that it had not been vaporized. The initial intense flash was emission from excited and ionized ambient gases near the impact surface, and had little relationship with shock temperature rise, indicating a new mechanism of impact flash.

The influence of different Mg concentrations on the mechanical properties and microstructure of an Al–Li alloy was studied. The highest Mg content was up to 1.1 wt.%. To the best of the authors knowledge, alloys with such a high Mg content has not been reported in the literature. The mechanical properties, yield strength and elongation at failure, of all of the alloys were investigated by tensile tests. Characterisation of the precipitates by analysing the dark field images and related diffraction patterns revealed that precipitation of the T1phase (Al2CuLi) was retarded by high (1.1 wt.%) Mg concentration. We hypothesized that a competition between the precipitation of T1phase and S' phase in high Mg containing alloy caused sluggish precipitation phenomenon and associated strengthening.

The influence of Ag on the microstructure evolution of an aged Al–Cu–Li–Mg alloy was studied. The coarse Cu-rich precipitates containing Ag and Mg were found during the whole ageing process of Al–Cu–Li–Mg–Ag alloy. Besides, Ag addition in the Al–Cu–Li–Mg alloy accelerates the hardness value reduction of the overaged alloy. When the alloy was over heat-treated, more coarse Cu-rich phases containing Ag and Mg are presented at the grain boundaries. These discrete coarse precipitates accelerate the hardness reduction of the overaged alloy.

The effects of solution time and cooling rate on microstructures and mechanical properties of 2219 Al alloy for a larger spun thin-wall ellipsoidal head are investigated. It is found that the Al2Cu phases are greatly affected by the solution time. The content of Al2Cu phases first decreases and then stabilizes with increasing the solution time. Moreover, the effects of solution time on the transformation of precipitates are obvious. As the solution time is increased from 35 min to 60 min, almost all the precipitates transfer from GP zones to θ′′ phases. When the solution time is further increased to 110 min, some θ′ phases appear. Meanwhile, the size of θ′′ phases increases, while the density of θ′′ phases drops. These microstructure changes greatly influence the mechanical properties, i.e., the hardness and tensile strengths first increase and then slightly decrease with the continuous increase of the solution time. In addition, if the cooling rate is decreased, the precipitation of coarse equilibrium θ phases is enhanced, but the precipitation of strengthening phases (θ′′, θ′) is restricted. It significantly deteriorates the mechanical properties. Based on the comprehensive analysis, the suitable solution time and cooling method are about 60 min and water cooling.

The tensile properties and corrosion behaviours of an ageing Al-1.7 Cu-4.0 Li- 0.4 Mg alloys (in at. %) with or without 0.3 Zn addition were investigated by detailed microstructure evolution using TEM and STEM. Herein, the Zn addition to the Al-1.7 Cu-4.0 Li- 0.4 Mg ageing alloy is determined as a convincing approach to optimising the strength-corrosion resistance balance. With Zn addition, the increasing quantity of T1phase in grain led to the increase of the tensile property of the Al-1.7 Cu-4.0 Li- 0.4 Mg alloy. While the studied alloy with Zn addition possessed preferable corrosion resistance in respect of intergranular corrosion (IGC) depth reducing. Moreover, the emergence of Zn elements in the coarse phases at grain boundary (GB) may decrease the potential differences between the precipitates at GB and free precipitation zone (PFZ), which could increase corrosion resistance.

Density functional theory was utilized to investigate the mechanism of Ru(II)-catalyzed aromatic C–H activation and addition of aromatic aldehydes. The proposed catalytic cycle consists of C–H bond activation, aldehyde carbonyl insertion for C–C coupling, lactonization for the formation of the final product, product separation, and catalyst recovery. Our calculations suggest that Ru(OAc)2(PCy3) (referred to as CAT) is the most favorable active catalyst, facilitating the C–H bond activation to form a five-membered ring cycloruthenium intermediate (INT2). Subsequently, the aromatic aldehyde reactant 2aenters the Ru coordination sphere, accelerating the C–C coupling and lactonization for the formation of the final product. The involvement of acetate assists in the final product separation, while INT1re-enters the Ru coordination sphere to initiate a new catalytic cycle. Utilizing the energetic span model, the apparent activation free energy barrier was computed to be 34.3 kcal mol–1at 443 K. Furthermore, exploration of the reaction mechanism in the absence of phosphine ligands identified Ru(OAc)2(p-cymene) as the most favorable active catalyst. The derived apparent activation free energy barrier offers a comprehensive explanation for the experimentally observed yields. Additionally, we have examined the disparities between the octahedral and trigonal bipyramidal structures of the catalysts concerning their effects on the reaction mechanisms and apparent activation free energy barriers.

The microstructures and mechanical properties of Al-3.35Cu-1.2Li-0.4Mg-0.4Zn-0.3Mn-0.1Zr (mass fraction, %) alloy with Sc addition or free Sc were investigated through tensile test, SEM, EPMA and TEM. The addition of 0.082% (mass fraction) Sc element leads to the formation of Cu-rich and Sc-contained nano-sized Al3(ScZr) particles and Wphase particles. The Al3(ScZr) particles can inhibit recrystallization to a certain extent and impede recrystallized grain growth during solution treatment. It is found that Wphase cannot dissolve in supersaturated solid solution during the solution heat treatment, and the Cu content in the solutionized matrix is decreased, which causes a decrease in the fraction of Cu-contained strengthening precipitates with T1(Al2CuLi) and θ′ (Al2Cu) under T8 aging condition. Due to the formation of the Wphases, the small Sc addition causes a little reduction in the strength.

The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys, 1460 alloy with a low Cu/Li ratio (1.46), 2050 alloy with a high Cu/Li ratio (4.51) and 2A96 alloy with a medium Cu/Li ratio (2.97), was investigated. The strength of the aged alloys is enhanced by the pre-deformation. The effectiveness of pre-deformation on precipitates is dependent on the alloy’s composition. With increasing the pre-deformation, the population density of T1 (Al2CuLi) precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys, and the greatest effectiveness is observed in 2A96 alloy. The pre-deformation also increases the population density of θ′(Al2Cu) precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys, but the effectiveness is smaller compared to that on T1 precipitates. In 1460 alloy subjected to two-step aging at 130 °C for 20 h followed by 160 °C for 12 h, the main precipitates are δ′(Al3Li). At 2%–6% pre-deformation, GP-I zones form and pre-deformation displays little influence. Eight percentage pre-deformation promotes θ″/θ′precipitation and increases their population density.

The hot deformation behavior and microstructure evolution of 1460 Al–Li alloy were investigated by isothermal compression test conducted at various strain rates (10−3–10 s−1) and temperatures (573–773 K). The flow stress curves were corrected by considering the friction at the platen/specimen interface and the temperature change due to the deformation heating. The effects of strain, strain rate and temperature on the deformation behavior were characterized by the Zener–Hollomon parameter in a hyperbolic-sine equation, and the constitutive equations were established according to the peak flow stress associated with dynamic recovery, dynamic recrystallization and the dissolution of T1phases. In the entire strain rate and temperature range, the prediction capabilities of the developed constitutive equation are proved to be feasible and effective with a linear correlation coefficient and an average absolute relative error coefficient of 0.9909 and 6.72%, respectively.

To enhance the approximation ability of process neural networks, a novel training algorithm is proposed by employing an improved quantum genetic algorithm. The proposed approach is applied to the training of process neural networks. The number of genes in a single chromosome is equal to the number of weight parameters. Taking each qubit in the current optimal chromosome as the goal, all individuals are updated by quantum rotation gate. In this method, each chromosome has three chains of genes, which can accelerate convergence. Taking the pattern classification of trigonometric functions as an example, the experimental results show that the proposed method is obviously superior to the common process neural networks.

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