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In order to improve the corrosion and heat resistance of Al-Mg-Si alloy conductor materials, Ce, Sc, Y and Zr were added in Al-Mg-Si alloy to regulate the microstructure. The Al-Mg-Si-Ce-Sc-Y alloy was designed with excellent pitting and intergranular corrosion resistance by obtaining the micron-sized Fe-containing second phase with a lower potential difference to Al matrix, more dispersed grain boundary precipitates with a higher proportion of Si particles, narrower width of PFZ and ideal distribution of intergranular precipitates. The Al-Mg-Si-Ce-Sc-Y alloy also maintained higher hardness, strength and electrical conductivity after overaging and annealing and the corrosion/heat resistance mechanisms were proposed. • The corrosion and heat resistance of Al-Mg-Si alloy conductors were further enhanced. • The mechanisms of pitting and intergranular corrosion mechanisms in Al-Mg-Si alloys were proposed. • The microalloying of Ce，Sc and Y in Al-Mg-Si alloys with high electrical conductivity was established. [ABSTRACT FROM AUTHOR]

Mechanical property and corrosion behavior of 7A46 aluminum alloy under peak-ageing (T6), double-ageing (DA) and pre-ageing (PA) followed by double-ageing (PA-DA) are systematically investigated. The hardness and strength of aged 7A46 alloy follows an order of T6>PA-DA > DA and the rank of corrosion resistance is PA-DA > DA > T6. The small size and dispersed distribution of matrix precipitates (MPs) lead to the high hardness and strength of T6 alloy, and low hetero-phase potential differences and less formation probability of corrosion galvanic couples enhance the corrosion resistance of PA-DA alloy. Intergranular corrosion (IGC) test results reveal that considerable potential differences promote the formation rate and the quantity of corrosive-batteries between the matrix and grain boundary precipitations (GBPs) or precipitate-free zones (PFZs). The exfoliation corrosion (EXCO) rate and the weight gain trend of corrosion products are related to the oxide film formation rate and corrosion products accumulation. Localized anodic dissolution and hydrogen embrittlement can induce the stress cracking corrosion (SCC). • The strengthen mechanism of 7A46 alloy is studied. • The mechanical strength is related to the small dispersed particles. • The alloy exhibits the best corrosion resistance under PA-DA condition. • The corrosion rate of the alloy under PA-DA condition is lower than that under T6, DA condition. [ABSTRACT FROM AUTHOR]

Abstract The localized corrosion behavior of Al-7.82Zn-1.99Mg-2.41Cu-0.12Zr alloy was investigated. At the early stage of corrosion, the sample surface only suffers slight local pitting corrosion. While as the immersion time extends, intergranular corrosion occurs, accompanied with surface exfoliation. At the initial stage of pitting corrosion, Al and Mg elements in the matrix around Al 7 Cu 2 Fe particles are dissolved preferentially, forming Al and Mg deplete zones. Furthermore, the dissolution of Al and Mg elements triggers the selective dissolution of Al element in Al 7 Cu 2 Fe, remaining Cu-rich and Fe-rich cluster. Atomic force microscopy (AFM) results show that this Cu-rich and Fe-rich cluster has higher potential difference relative to the matrix than the uncorroded Al 7 Cu 2 Fe particle. Highlights • The effects of Al 7 Cu 2 Fe on the localized corrosion behavior of alloy were investigated. • AFM technique was used to measure the potential difference between Al 7 Cu 2 Fe and matrix. • The corroded Al 7 Cu 2 Fe has higher potential difference relative to the matrix than the uncorroded Al 7 Cu 2 Fe. • Pitting corrosion initiation mechanism was studied in detail. [ABSTRACT FROM AUTHOR]

Abstract The changes of stress level for the ultra-high strength Al-Zn-Mg-Cu-Zr alloy were described by constitutive equation with considering lattice diffusion of aluminum, zinc, magnesium and copper. Zener–Hollomon (Z) parameter expression based on the constitutive equation with considering lattice diffusion was used to reflect the changes of microstructure. The critical stress σ c for the initiation of dynamic recrystallization (DRX) was introduced to calculate the Z parameter. Steady-state dislocation density ρ sat and critical dislocation density ρ c for the initiation of DRX decreased with the increase of deformation temperature. The dependence of diffusion activation energy Q on temperature and strain rate was given and the effects of deformation conditions on Q were discussed in detail. Microstructural evolution revealed that low angle boundaries (2–5°) created in the process of dynamic recovery (DRV) could convert into subgrain boundary, thus the original grains were divided into subgrains, and then subgrains transformed into DRX grains by the way of progressive rotation. When the Z value was high (ln Z > 30.9), DRV was the main softening mechanism. With the decrease of Z value, both of DRV and DRX played an important roles in softening effect, while with the further decrease of Z value (ln Z < 28.6), DRX became the main softening mechanism. Continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) operated together under the condition of lower Z value, but CDRX was confirmed as the dominant DRX mechanism. Highlights • The dislocation density under different deformation conditions was calculated. • The Z parameter based on the model with considering lattice diffusion was constructed. • The effects of deformation conditions on diffusion activation energy were discussed. • The effects of Z parameter on deformation mechanism were discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract To obtain the optimal mechanical properties, several processes including spray forming technology, two passes hot extrusion and substantial heating treatments were operated on an Al-Zn-Mg-Cu-Zr alloy. The characterization methods used in this study include tensile tests, X-ray diffraction, differential scanning calorimetry and microstructure observations by optical microscope, scanning and transmission electron microscopy. The typical characteristics were the refined grain, homogeneous precipitates and porosity in the as-deposited pre-forms. The ultimate tensile strength, yield strength, hardness and elongation improved significantly after two passes hot extrusion. A good combination of ultimate tensile strength at 704 MPa and elongation at 9.7% were achieved under peak-aged treatment. The best ultimate tensile strength was obtained at 732 MPa after re-aging and regression. It was main dimple fracture in the extruded and aging treated specimens while brittle fracture for the as-deposited. The secondary phases were main MgZn 2 and Al 3 Zr dispersoids throughout all the states. The contributions of grain boundaries, dislocations, solid-solution and precipitates on the yield strength were analyzed using a quantitative equation. Highlights • The spray forming technology was used to fabricate ultra-high strength aluminum alloy. • The alloy under RRA state obtained the highest ultimate tensile strength of 732 MPa. • The effects of dislocations, solutes and precipitates etc., on yield strength were calculated. • Precipitation was characterized as the main strengthening mechanism for aging states. [ABSTRACT FROM AUTHOR]

Millions of tons of iron-bearing manganese residue are produced as a by-product of the electrolytic manganese industry. And the environmental contamination caused by manganese residue has received increasing attention. This paper focuses on the recovery of iron and manganese from high iron-bearing manganese residues. Manganese ferrite in manganese residues is initially decomposed by oxidative roasting, and the intermediates are magnetized in a reductive roasting step. The roasted product is milled and subjected to multi-stage magnetic separation. The optimum conditions are as follows: roasting at 750 °C under air flow for 30 min, roasting in a CO atmosphere at 750 °C for 30 min, and separating under a magnetic intensity of 1000 G for weak magnetic separation and of 12,000 G for strong magnetic separation. The recovery and grade of iron in the iron concentrate were 72.29% and 62.21%, respectively, and those of manganese in the manganese concentrate were 90.75% and 35.21%, respectively. This study demonstrates that the combination of roasting and magnetic separation provides a promising process for the recovery of iron and manganese from high-iron-bearing manganese residues. [ABSTRACT FROM AUTHOR]

Ultra-high strength Al-Zn-Mg-Cu alloy extrusion bars were processed by equal channel angular pressing (ECAP) at room temperature (RT). Post aging treatment was used to determine the optimum time of aging. ECAPed sample was divided into two types: near the upper channel (P1) and lower channel (P2). Micro-hardness and tensile tests showed that ECAPed sample reached peak aging state at 8 h, which greatly shortened the time to T6 state. The mechanical properties of ECAPed samples were also better than traditional T6 samples. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) were used to study the phase transformation from extrusion bars to ECAPed samples. AlZnMgCu phase and Al 2 CuMg phase containing Zn can be found in ECAPed sample. Meanwhile, the coarsening phase Al 7 Cu 2 Fe decreased significantly. Optical microscopy (OM) and transmission electron microscopy (TEM) were used to analyze the microstructure evolution such as shear bands and grain size during ECAP process. In P1, the shear bands with width ranging from 90 to 300 µm can be found. These shear bands were divided into many thinner shear bands and became intragranular deformation bands gradually in P2. Compared with P2, the average grain size in P1 decreased greatly and the precipitate η′ phase became finer and denser. Grain boundary strengthening and precipitation strengthening in P1 were much better than P2. The diameter of the channel should not exceed 20 mm when it used to press ultra-high strength Al-Zn-Mg-Cu alloy and the 3/4 parts near the top channel of product should be used to avoid unrefined grains. [ABSTRACT FROM AUTHOR]

In order to improve the surface performance of Al-Zn-Mg-Mn-Zr extruded alloy, alumina coatings were directly prepared on the alloy in silicate electrolytes by direct current micro-arc oxidation technique. The relationship between discharge stages and technology parameters was studied, and then the growth behaviors, structure, composition and properties of coatings were further analyzed. Our work suggests that appropriately prolonging of the oxidation time at a low current density of 2 A/dm 2 can help to extend the action time of the micro-arc stage (Stage III) and to form a thicker layer with fewer inner defects. The compact inner structure promotes the hardness, elastic modulus as well as the corrosion resistance of the coatings. In contrast, the higher the current density, the earlier the discharge enters into the big arc stage (Stage IV), which has an adverse impact on the structure and properties of the coatings. In the Stage IV, the porosity of the coatings increases with the generation of mullite within the coatings comprise of γ-Al 2 O 3 and α-Al 2 O 3 . The growing direction of coatings changes from outward mainly to inward in the late stage of the micro-arc oxidation (MAO) process. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of spray formed ultra-high strength aluminum alloy was investigated by isothermal compression tests at 613–723 K and 0.001–1.0 s −1 . The flow stresses were predicted by using phenomenological model (strain-compensated Arrhenius equation), physical-based model (diffusion model) and artificial neuron network. The predictive ability has been weighed through statistical analysis including relative errors, correlation coefficients and box charts. It has shown the artificial neural network contains the best capability to predict the flow stress over the applied phenomenological and physical-based model. The strain-compensated Arrhenius can track the flow stress well in all processing conditions. Moreover, the diffusion model can well describe the metallurgical mechanisms during deformation by the microstructure observation. [ABSTRACT FROM AUTHOR]

Isothermal hot compression tests of Al-7.82Zn-1.96Mg-2.35Cu-0.11Zr alloy were carried out on a Gleeble-3500 thermo-simulator in the temperature range of 573–733 K and strain rate range of 0.001–1 s −1 . Stress-strain curves show that work hardening effect progressively exceeds softening effect with increasing strain rate. Microstructural evolution shows that two kinds of dynamic recrystallization exist in the hot compression process, which includes continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) and the dominant mechanism is continuous dynamic recrystallization, which occurs under the combined action of progressive subgrain rotation and misorientation increase. Five constitutive models were constructed to describe the hot deformation behavior. Weight optimization model has lower average absolute relative errors (AARE) value of 2.78%, root mean square error (RMSE) value of 2.73 and higher correlation coefficient (R) value of 0.997, and gives weight factors at different temperatures. The revised constitutive model with considering the comprehensive effects of lattice diffusion, grain boundary diffusion and the results of weight optimization gives relatively high prediction precision with AARE value of 4.64%, RMSE value of 4.92 and R value of 0.995, which is second to that of weight optimization model. The main diffusion mechanism is dominated by grain boundary diffusion at 573–693 K and lattice diffusion at 733 K. [ABSTRACT FROM AUTHOR]

The superplastic behavior of Al–Mg–Sc–Zr samples with standard gauge size (18 mm by 6 mm) were prepared using simple rolling and were tested in the temperature range from 450 °C to 525 °C at strain rates ranging from 1.67×10 –3 s −1 to 1×10 –1 s −1 . With proper deformation parameters, the Al–Mg–Sc–Zr alloy has an elongation to failure much higher than 300% and the maximum elongation is 740%. The Microstructure and dislocation substructure investigation using optical microscopy (OM) and transmission electron microscopy (TEM) revealed a dynamic recrystallization in it. The grain size and activation energy on the deformation mechanisms of superplastic is discussed. Results also show that these nano-scale Al 3 (Sc 1−x Zr x ) particles play an important role in the superplastic process. Al 6 FeMn particles were found to induce the formation and growth of cavities, which can lead to the fracture of specimens. [ABSTRACT FROM AUTHOR]

Extruded plates of 6005A aluminum alloy with 0.07 wt% Sc (referred to as M6005A alloy) was metal-inert-gas-welded (MIG-welded) with ER5087 filler wire. The microstructure, mechanical properties, and fatigue behavior of the joints were studied. Compared with the base material (BM), recrystallization occurred and the formation of the coarse β' phase was evident in the heat-affected zone close to the weld zone (HAZ 2), which resulted in a significant decrease in the mechanical properties of HAZ 2. However, trace Sc inhibited the growth of the recrystallized grains in the HAZ 2, strengthening the α-AlFeSi and β'′ phases in the BM, which drastically improved the mechanical properties of the BM. In the weld zone (WZ), grains were significantly refined since the presence of Al 3 (Sc, Zr) particles promoted the nucleation of such grains in the WZ, and the particles also promoted the non-uniform nucleation of the α-AlFeSi phase, which significantly improved the mechanical and fatigue properties of the WZ. The hardness distribution of the MIG-welded joint shows a double-W shape. The lowest hardness is 55 HV, observed in the HAZ 2. The ultimate tensile strength (UTS) and conditional fatigue strength (107 cycles) of the MIG-welded joint of M6005A-T6 are 238.5 MPa and 108.2 MPa, respectively, 38 MPa and 13 MPa higher than the those of the MIG-welded joint of 6005A-T6 alloy, respectively. • The 6005A alloy profile, with optimum content of Sc, was welded by MIG welding. • Study on microstructure and properties of welding joint of 6005A alloy containing Sc(referred to as M6005A-T6 alloy). • The mechanism of the effect of Sc on the structure and properties of 6005A welded joint was studied. • M6005A alloy is about to replace 6005A alloy as an important material for high-speed iron‑aluminum. [ABSTRACT FROM AUTHOR]

Mechanical property and corrosion resistance are essential performances in ultra-high strength Al-Zn-Mg-Cu alloys for the aerospace and weapon industries. In this study, the pre-strain and aging treatments were used to enhance such performances of the spray formed ultra-high strength Al-Zn-Mg-Cu alloy. After 2% pre-strain with peak aging (PA) and retrogression and re-aging (RRA) treatments, the ultimate tensile strength, yield strength, and elongation can reach to 774 MPa, 735 MPa, 10.7% and 774 MPa, 747 MPa, 9.4%, respectively. The coarser precipitates of the samples with 4% pre-strain can lead to the slight lower strength compared with the samples with 2% pre-strain. The proper combination of pre-strain and aging treatments can also effectively enhance the stress corrosion resistance of the studied alloy by the following reasons. First, the higher strain concentration degree and dislocation density introduced by pre-strain treatments have high internal energy and provide more stored energy for the growth of the passive film. Second, the spacing of grain boundary precipitates under double aging (DA) and RRA states is larger than that under PA state. The width of uniform precipitation free zone (PFZ) with 2% pre-strain is larger than that with 4% pre-strain. Third, after pre-strain treatments, the cracks perpendicular to the deformation direction can be produced in Al 7 Cu 2 Fe phase, which further breaks up such particles. According to the results of Kelvin probe microscopy, the Al 7 Cu 2 Fe phase with smaller dimension can obtain the lower difference of potential to Al matrix. • The strength and corrosion resistance of the alloy were enhanced by pre-strain. • The pre-strain produced cracks in Al 7 Cu 2 Fe particles and further broke up them. • The pre-strain improved the strain concentration degree and dislocation density. • The effect of precipitation free zone and precipitate is better under 2% strain. • The improvement mechanism of pre-strain treatment was revealed. [ABSTRACT FROM AUTHOR]

• Preparation of new-type Sc-containing 6005A aluminum alloy by ingot metallurgy. • The microstructure evolution, mechanical properties and fatigue behavior of 6005A alloy under different ageing are studied. • Established the aging system with the best anti-fatigue performance. A new type of alloy, modified based on 6005A alloy, with addition of 0.06% Sc was prepared by ingot metallurgy. The alloy ingots were homogenized, extruded, quenched and solution-aged into 8 mm thick plates. The effect of different aging treatments on the fatigue properties of 6005A alloy was investigated. It is revealed that optimum resistance against fatigue crack growth (FCG) was obtained in the under aged (UA) sample. The lowest fatigue crack growth rate (FCGR) was evident in the UA sample compared with the peak aged (PA) and over aged (OA) samples. [ABSTRACT FROM AUTHOR]

In the present work, laser shock peening was applied to the ultra-high strength Al-Zn-Mg-Cu alloys prepared by ingot metallurgy and spray forming. The microstructural evolution, pitting corrosion, intergranular corrosion resistance and electrochemical analysis were systematically investigated. The depth and number of corrosion pits caused by Al matrix, Al 7 Cu 2 Fe and Al 2 CuMg particles can be successfully reduced by laser shock peening. The depth of intergranular corrosion and the width of intergranular cracks also decreased. Cyclic polarization and electrochemical impedance spectroscopy tests also indicated the improved corrosion resistance caused by laser shock peening. The relationship between microstructural evolution and corrosion resistance was studied. • Corrosion resistance of ultra-high strength Al-Zn-Mg-Cu alloys is promoted by laser shock peening. • Al 2 CuMg and Al 7 Cu 2 Fe phases act as preferred sites for pitting corrosion. • Al 2 CuMg phase can cause deeper corrosion pits than Al 7 Cu 2 Fe phase. • Depth of pitting and intergranular corrosion are ameliorated by laser shock peening. • Residual compressive stress, line and surface defects is conducive to corrosion resistance. [ABSTRACT FROM AUTHOR]

The effects of solution treatment on microstructural and mechanical properties of a novel Al–Zn–Mg alloy by microalloying with Sc and Zr were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), transition electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), differential scanning calorimeter (DSC), X-ray diffraction and tensile test, hardness measurement, respectively. The results show that solution treatment had a significantly effect on microstructural and mechanical properties. There exist lots of residual phases along rolling direction before solution treatment. With increasing solution temperature/time, the residual phases are dissolved into α-Al matrix gradually, and the number density of residual phases decreased. After solution treatment at 460°C/60 min and aging treatment at 120°C/24 h, the precipitated phase inside the grains are homogenously distributed η ′ phase; the distribution of η precipitates is discontinuous and coarsened on the grain boundary. With the increase of solution temperature(≤470 °C) or solution time(≤60 min), the precipitated phases inside the grains began to become more diffuse, and the grain boundary precipitated phases also gradually become smaller. When solution temperature further increased to 490 °C or solution time increased to 120 min, the precipitated phases within the grains and on the grain boundary began to coarsen. In addition, there also exists lots of fine Al 3 (Sc, Zr) particles during aging treatment. Both tensile strength and hardness increase first and then decrease with increasing solution temperature or solution time. The optimum solution treatment is 470°C/60 min. The ultimate tensile strength, yield strength and elongation of the aged studied alloys reached a maximum value, 581 MPa, 561 MPa, and 10.1%, respectively. [ABSTRACT FROM AUTHOR]

Microstructural and property evolution of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy sheet during its preparation were investigated in detail by means of optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Vickers micro-hardness test and room temperature tensile test. Stress corrosion cracking (SCC) behavior of the Al–Zn–Mg–0.10%Sc–0.10%Zr alloy under different heat treatments was studied using slow strain rate test. The results showed that serious dendritic segregation existed in as-cast condition. The suitable homogenization treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was 470 °C/24 h. After homogenization treatment, dissoluble Zn and Mg enriched non-equilibrium phases dissolved into α -Al matrix completely. The suitable solid solution-aging treatment for Al–Zn–Mg–0.10%Sc–0.10%Zr alloy was solution treated at 470 °C for 60 min, followed by water quenching and then aged at 120 °C for 24 h. Under this aging temper, the grain structures were composed of sub-grains, η ʹ phases and nanometer-sized, spherical Al 3 (Sc, Zr) particles. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The improved corrosion resistance from increasing aging temperature or prolonging aging time was due to the discontinuous η precipitates along the grain boundary and the high area fraction of GBPs. The main strengthening mechanisms of Al–Zn–Mg–0.10%Sc–0.10%Zr alloy are precipitation strengthening derived from η ʹ precipitates, dispersion strengthening, sub-grain strengthening and grain refinement caused by coherent Al 3 (Sc, Zr) particles. [ABSTRACT FROM AUTHOR]

The precipitation behaviour, mechanical properties and corrosion performance of an Al-Zn-Mg-Sc-Zr alloy under one-stage aging (T6), two-stage aging (T74) and retrogression and re-aging (RRA) treatment were mainly investigated. For the RRA treatment, with increasing temperature and duration of retrogression, the grain interior precipitates (GIPs) gradually grew and changed from GP zones + η′ phases to η′ phases + η phases. In addition, the discontinuity of coarsened grain boundary precipitates (GBPs) significantly increased, and the width of precipitate free zones (PFZs) became broader. Consequently, progressive decrease in strength and hardness, and improved corrosion resistance of the alloy can be observed. Compared to conventional T6 and T74 treatments, a good balance of mechanical properties (168.5 HV for hardness, 547 MPa for ultimate tensile strength) and corrosion resistance can be obtained with retrogression treatment at 160 °C for 30 min. Moreover, research on the localized corrosion of the Al-Zn-Mg-Sc-Zr alloy showed that, at the initial stage of pitting corrosion, the Al matrix around the cathodic α-Al(Fe,Mn)Si particles was uniformly dissolved, leading to the detachment of the α-Al(Fe,Mn)Si particles from the matrix and the formation of pitting pits. • The strengthening and corrosion mechanisms of Al-Zn-Mg-Sc-Zr alloy under different aging conditions were studied. • A model for the process of pitting corrosion development is established. • The optimized RRA treatment for Al-Zn-Mg-Sc-Zr is obtained. [ABSTRACT FROM AUTHOR]

2.5 mm thick cold-rolled Al–Zn–Mg–Zr alloy plates with trace amount of Sc were subjected to metal–inert gas (MIG) welding with Al–Mg–Sc as the filler metal. The influence of Sc additions on microstructure and mechanical properties of the welded joints was investigated by means of optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), Vickers micro-hardness test and room temperature tensile test. Experimental results indicated that trace amount of Sc had significant effect on microstructure and mechanical properties of the joints. In both cases, base metal consisted of a typical fiber structure, different width of the equiaxed zones (EQZs) with fine grains were observed in the weld metal at the fusion boundary, fusion zones exhibited dendritic microstructure and average size of Al–Zn–Mg–0.10%Sc–Zr was 120 μm, while in Al–Zn–Mg–0.25%Sc–Zr, grain size decreased drastically to 50 μm. The grain refinement is mainly caused by the extremely fine, coherent Al 3 (Sc, Zr) particles with L1 2 structure, which act as heterogeneous nucleation. The observed grain refinement resulted in an appreciable increase in fusion zone strength and micro-hardness. Tensile strength of Al–Zn–Mg–0.25Sc–Zr alloy welded joint was 460 MPa, approximately 11% higher than Al–Zn–Mg–0.10Sc–Zr alloy welded joint. Micro-hardness in the center of fusion zone rose from 95 HV to 110 HV. The main strengthening mechanisms of Al–Zn–Mg–Sc–Zr MIG welded joints are precipitation strengthening derived from η′ precipitates, dispersion strengthening and fine grain strengthening caused by coherent secondary Al 3 (Sc, Zr) particles. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) behavior of Al–Zn–Mg–Cu alloys with different Sc, Zr contents and heat treatments was studied using slow strain rate test. Grain boundary microstructures were identified by transmission electron microscopy (TEM) and statistical analysis. It was found that the SCC resistance of alloys is improved by increasing Sc, Zr contents and aging degree. Grain boundary precipitates (GBPs) area fraction was found to be an important parameter to evaluate the SCC susceptibility. The results reveal that for Al–Zn–Mg–Cu–0.25Sc–0.10Zr (wt%) alloy with different aging degrees, hydrogen induced cracking dominates the SCC when the area fraction of GBPs is relatively low. For peak-aged Al–Zn–Mg–Cu alloy and Al–Zn–Mg–Cu–0.10Sc–0.10Zr (wt%) alloy, anodic dissolution dominates the SCC when the area fraction of GBPs is sufficiently high. [ABSTRACT FROM AUTHOR]

Microstructures and properties of Al–Zn–Mg–Mn alloy with trace amounts of Sc and Zr have been investigated. The results show that the addition of minor Sc and Zr to Al–Zn–Mg–Mn alloy can effectively refine grain size caused by the formation of Al 3 (Sc, Zr) particles with cubic L1 2 structure, which is coherent with α(Al) matrix. After solution treatment at 470 °C for 1 h, more homogenous recrystallization grains are observed in Al–Zn–Mg–Mn alloy; partial recrystallization occurs in Al–Zn–Mg–Mn–0.12Sc–0.12Zr alloy. However, Al–Zn–Mg–Mn–0.24Sc–0.12Zr alloy still remains an unrecrystallized fiber-like structure, which reveals that minor Sc and Zr can remarkably inhibit the occurrence of recrystallization. After aging treatment at 24 h for 120 °C, the tensile strength of Al–Zn–Mg–Mn–0.12Sc–0.12Zr alloy increased by 40 MPa as compared to Al–Zn–Mg–Mn alloy. When the Sc content increased to 0.24 wt%, the tensile strength of Al–Zn–Mg–Mn–0.24Sc–0.12Zr alloy reached a maximum. The main strength mechanisms are grain refinement strengthening with combined Sc and Zr additions and precipitation strengthening of Al 3 (Sc, Zr) particles. Compared with Al–Zn–Mg–Mn alloy, Al–Zn–Mg–Mn alloy with trace amounts of Sc and Zr exhibits higher corrosion resistance due to the discontinuity distribution of η precipitates along the grain boundary and the resistance effect on recrystallization behavior by Al 3 (Sc,Zr) particles. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al–Cu–Li–Sc–Zr alloy and its microstructure evolution were investigated by isothermal compression tests under various deformation conditions. The tests were carried out in the deformation temperature range between 380 and 500 °C and at strain rates between 0.001 and 10 s −1 . The constitutive model based on the hyperbolic-sine equation was established to characterize the dependence of flow stress on strain, strain rate and deformation temperature. Based on the experimental data and dynamic materials model, the processing maps at strain of 0.4 and 0.6 were generated to demonstrate the hot workability of the alloy. The results show that the flow stress decreases with increasing deformation temperature, and increases with increasing strain rate. The main softening mechanism is dynamic recovery at 440 °C/0.1 s −1 ; the dynamic recrystallization of the alloy can be easily observed at 470 °C/0.001 s −1 , with peak efficiency of power dissipation of around 57%. With increasing deformation temperature, the volume fraction of dynamic recrystallization increases. At strains of 0.4 and 0.6, the flow instability domain is found at higher strain rates (>0.3 s −1 ), which mainly locates at the upper part of processing maps. On the basis of processing maps and microstructure evolution, the optimum hot working parameters are in deformation temperature range from 460 to 500 °C and at strain rate range from 0.001 to 0.1 s −1 with higher power efficiency of around 42–60%. [ABSTRACT FROM AUTHOR]

Highlights: [•] Anisotropy of fatigue growth rate is different from strength and toughness. [•] Fatigue behaviors are analyzed based on crystallographic model and Schmid factors. [•] Twist angle differences determine the intergranular or transgranular propagation. [•] Crack deflection and branch depend on slip systems and loading stress. [Copyright &y& Elsevier]

• The effects of Sc, Y and Zr on the performances and microstructure evolution of Al-0.7Mg-0.6Si-0.2Ce alloys were studied. • An excellent combination of strength, elongation and electrical conductivity was achieved with the addition of Sc and Y. • The strengthening and electrical resistance mechanism of the studied alloys were revealed by statistical calculation. [Display omitted] In order to achieve the compatibility between excellent mechanical properties and good electrical conductivity of Al-Mg-Si alloys, detailed investigation was carried out to understand the microstructure evolution and their influences on performances of different Al-0.7Mg-0.6Si-0.2Ce-X (X Sc, Y and Zr) alloys prepared by casting, homogenization, hot extrusion, solution and aging treatments. Under aging state, Ce can form a large number of micron-sized AlCeSi and a few AlCeFeSi phase. The strength increased to 334 MPa as a result of decreased grain size and improved precipitation effect and the electrical conductivity increased up to 53.53%IACS because of lower solute Si atoms. The β" precipitates were coarsened and consequently the volume fracture was largely reduced due to the presence of Sc element, leading to the decreased strength of 311 MPa. The more solute Mg, Si and Sc atoms increased the degree of free electron scattering and the electrical conductivity decreased to 51.86%IACS. It is also found that Sc significantly enhanced the elongation of the alloy from 11.8% to 18.0%, which might be attributed to the formation of Al 3 Sc and (Al, Si) 3 Sc phases. The addition of Y raised the electrical conductivity of Al-Mg-Si-Ce alloy to 55.79%IACS by ameliorating the volume fraction and distribution of β" precipitates and decreasing the solute Si atoms. The co-addition of Sc and Y inherited the advantages of such two alloys. The ultimate tensile strength, elongation, electrical conductivity of Al-0.7Mg-0.6Si-0.2Ce-0.2Sc-0.1Y alloy processed by aging treatments is 336 MPa, 19.4% and 53.11%IACS, respectively. [ABSTRACT FROM AUTHOR]

Abstract: The Al–Mg–Sc alloy sheets were prepared using water chilling copper mold ingot metallurgy processing which was protected by active flux. The microstructure and mechanical properties of the Al–Mg–Sc alloy were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM) and tensile and fatigue crack growth (FCG) rate tests. The FCG rate (da/dN) with stress intensity factor range (ΔK) was discussed within the Paris region. The Al–Mg–Sc alloy exhibited high resistance against fatigue crack growth, and the second phase of Al3(Sc1−x Zr x ) was found to be the main factor influencing the FCG resistance. [Copyright &y& Elsevier]

Highlights: [•] Investigate effect of aging temperature on corrosion behavior of an Al–Zn–Mg–Sc–Zr alloy. [•] Find the relationship between corrosion and microstructures of the studied alloy. [•] Corrosion behavior is determined using both electrochemical and immersion tests. [•] Improvement is due to absence of coarse precipitates and precipitate-free zones. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot compression test were conducted under different deformation conditions. [•] The dynamic recovery and dynamic recrystallization occurred during hot deformation. [•] ANN model and constitutive equations were established to predict the flow stress. [•] Material constants and Q value in the constitutive equations were calculated. [•] ANN model has a better prediction power than constitutive equations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot deformation behavior of X-750 superalloy was investigated. [•] Processing maps were developed. [•] Flow instability regions identified and the mechanism was evaluated. [•] Optimum processing parameters were given. [ABSTRACT FROM AUTHOR]

The effects of trace Sc and Y on the corrosion behaviors of cold-drawn Al-0.2Ce alloys were revealed by scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Electron Probe Micro-analyzer (EPMA), and electrochemical measurements. The results showed that the Al 3 Sc particles not only enable the increase of subgrain boundaries in the modified alloy after cold drawing but also improve the morphology and size of the Al 13 Fe 3 Ce phase. SKPFM analysis showed that the enrichment of Y around the Al 13 Fe 3 Ce phase in the modified alloy can decrease its electrochemical inertness and thus reduce the micro-galvanic corrosion susceptibility of the alloy. The results of the electrochemical analysis showed that the individual and composite addition of Sc and Y can improve the corrosion resistance of the cold-drawn Al-0.2Ce alloy. The corrosion potential and current of Al-0.2Ce-0.2Sc alloy are −0.892 V and 0.91 μA·cm−2, while the corrosion potential and current of Al-0.2Ce-0.1Y alloy are −0.918 V and 1.08 μA·cm−2, respectively. It is obvious that Sc element improves the corrosion resistance of Al-0.2Ce alloy more effectively than Y element. The corrosion depth of Al-0.2Ce-0.2Sc-0.1Y alloy was the smallest tested by immersion under the same conditions, and its corrosion potential and corrosion current were −0.842 V and 0.79 μA·cm−2, respectively, corresponding to the best corrosion resistance. The formal mechanism of pitting corrosion in the alloys is also discussed. [Display omitted] • Effect of Sc on microstructure and corrosion of Al-0.2Ce alloy was revealed. • The enrichment of Y atoms around Al 13 Fe 3 Ce can reduce the potential difference. • The corrosion behaviors of pitting corrosion induced by Al 13 Fe 3 Ce was discussed. • The equivalent circuit of the studied alloys was identified. [ABSTRACT FROM AUTHOR]

Abstract: The flow behavior of Al–Zn–Mg–Sc–Zr alloy and its microstructural evolution during hot compression deformation were studied by thermal simulation tests. The tests were carried out in deformation temperature range from 340 to 500°C and at strain rate range from 0.001 to 10s−1. The results show that deformation temperature and strain rate have significant influence on the flow behavior of Al–Zn–Mg–Sc–Zr alloy. The flow stress increased with increasing strain rate, and decreased with increasing deformation temperature. In order to demonstrate the workability of Al–Zn–Mg–Sc–Zr alloy further, the processing maps at strain of 0.3 and 0.5 were established respectively based on dynamic materials model. The dynamic recrystallization of Al–Zn–Mg–Sc–Zr alloy occurred at deformation temperature of 420°C and a strain rate of 0.01s−1. At higher deformation temperature or lower strain rate, the grain size as well as the volume fraction of the recrystallized grains increased. At strain of 0.3 and 0.5, the flow instability domain mainly located at higher strain rate (>0.4s−1). On the basis of the processing map and microstructural evolution, the optimum processing conditions at a strain of 0.3 are in the strain rate range of around 0.001–0.1s−1 and deformation temperature range between 380 and 440°C. [Copyright &y& Elsevier]

Abstract: The behavior of the flow stress of Al–Cu–Mg–Ag heat-resistant aluminum alloys during hot compression deformation was studied by thermal simulation test. The temperature and the strain rate during hot compression were 340–500°C, 0.001s−1 to 10s−1, respectively. Constitutive equations and an artificial neural network (ANN) model were developed for the analysis and simulation of the flow behavior of the Al–Cu–Mg–Ag alloys. The inputs of the model are temperature, strain rate and strain. The output of the model is the flow stress. Comparison between constitutive equations and ANN results shows that ANN model has a better prediction power than the constitutive equations. [Copyright &y& Elsevier]

Abstract: A ZK60 alloy was processed by two-step equal channel angular pressing (ECAP) in order to refine the grain size and enhance the mechanical properties. The results show that fine grain size less than 1μm was obtained after the two-step ECAP process, 4 passes at 513K, followed by another 4 passes at 453K. The strength of ZK60 alloy decreased after the single-step ECAP process but recovered after two-step ECAP process. The strength decrease was related to the texture softening. Compared with the single-step ECAP at 513K, the two-step ECAP has significantly improved the yield strength and ultimate tensile strength of the alloy. The mechanism of the notable grain refinement of the ECAP process was mainly attributed to continuous dynamic recovery and recrystallization. [Copyright &y& Elsevier]

Sc-containing Al alloys have excellent mechanical properties, which provide the foundation for their applications. The precipitation of the Al 3 Sc/Al 3 (Sc, Zr) is generally considered to be a key factor for the performance boost. However, the performances of the alloy in different production batches often exhibit unstable and fluctuation, which may be related to the heterogeneous of scandium. Herein, we investigated the precipitation behaviors of Al 3 Sc/Al 3 (Sc, Zr) phases in the Al-0.5Sc and Al-0.5Sc-0.25Zr alloys at 340 °C. Results shown that the high scandium‑zirconium ratio not only lead to the discontinuous precipitation, but also contribute to the abnormal continuous Al 3 (Sc, Zr) precipitation in Al-0.5Sc-0.25Zr alloy. The morphology of abnormal Al 3 (Sc, Zr) is similar to the common secondary Al 3 (Sc, Zr) phase with a coffee-bean like morphology. With the aid of Three-Dimensional Atomic Probe (3DAP), the core-shell structures of Al 3 (Sc, Zr) phases are quantitatively analyzed. In the shell layer of abnormal Al 3 (Sc, Zr) phase, the atomic concentration ratio of Sc to Zr is much higher than the common continuous precipitated Al 3 (Sc, Zr) phase. The abnormal Al 3 (Sc, Zr) phase may be one of the key factors for the structure heredity of Sc-containing Al alloys. [Display omitted] • The discontinuous precipitated Al 3 Sc phases are related to the partial high ratio of Sc/Zr (at.%) in Al alloys. • The discontinuous precipitated Al 3 Sc phases form at the casting process and gradually decompose at annealing process. • The high scandium-zirconium ratio leads to the decrease of coarsening resistance of the secondary Al 3 (Sc, Zr) phase. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new type of multi-scale porous copper foams was developed by composite electroplating and subsequent heat treatment. They contain macro pores and finer or micro ones with pores size of about 300μm and 5–20μm respectively, performing different functions in a capillary action when they are used in thermal management devices such as heat pipe, vapor chamber etc. The large pores help reduce the resistance to liquid flow and accommodate more liquid, and the small pores enhance the capillary performance. In comparison with the manufacturing processes for traditional wick structures such as sintered metal powders, meshes or micro channels, the multi-scale porous copper foams are more advantageous as they are more cost effective and can be done at a higher production rate. [Copyright &y& Elsevier]

In ultra-high strength Al-Zn-Mg-Cu alloys, traditional heat treatments such as peak aging, two-stage aging and retrogression and re-aging cannot perfectly balance the relationship between mechanical properties and corrosion resistance and usually consume more time. Based on previous studies, the aim of this paper is to establish a suitable non-isothermal aging method for ultra-high strength Al-Zn-Mg-Cu alloys. In this study, after enhanced solution treatment and aging process with the heating rate of 20 °C/h, the alloy achieves excellent hardness and ultimate tensile strength of 195.7 HV and 680 MPA, respectively. When heating rate increases to 40 °C/h, non-isothermal aging can also ensure the alloy achieve the excellent mechanical properties (195.6 HV, 675 MPA). Similar to mechanical properties, the samples have outstanding resistance to intergranular and exfoliation corrosion, which is in accordance with the results of potentiodynamic polarization and electrochemical impedance spectroscopy tests. Evidences from high resolution transmission electron microscopy show that non-isothermal aging can promote the formation of a large number of smaller GP zones, η' precipitates and few η 2 precipitates inside grains, which greatly strengthens the mechanical properties. Furthermore, the grain boundaries precipitates transform from continuous to discontinuous and precipitate free zones form gradually, which greatly enhances the corrosion resistance. Because of these precipitates inside grains and grain boundaries, the samples with enhanced solution treatment +20 °C/h aging process and both solution treatments +40 °C/h aging process can achieve good mechanical properties closing to T6 state and corrosion resistance similar to T74 state simultaneously with much less aging time. Image 1 • The non-isothermal aging was designed as a novel route for heat treatments of ultra-high strength Al-Zn-Mg-Cu alloy. • An excellent combination of strength-ductility and corrosion resistance was achieved in the studied alloy. • The strengthening and corrosion mechanisms of non-isothermal aging on the studied alloy were discussed systematically. • Precipitation behavior of MgZn 2 strengthening phase was well studied. [ABSTRACT FROM AUTHOR]

The morphology of primary Al 3 Sc phase in Al-2.2Sc(wt%) was found to be influenced by melting condition. Some representative morphology appeared in large quantities at specific melting temperatures, holding times, and cooling rates. Crystallography of primary phases with various morphologies was researched, and the growth processes of the primary phase were investigated. Deformed cubes and dendrite can be developed from cubes, the butterfly-like particles had multiple layers inside, and repeated eutectic reactions were the main reason for the formation of multilayer structures. Al-2.2Sc(wt%) master alloys with different morphologies of primary Al 3 Sc phase can lead to different refining effects, and the mechanical properties of alloys were consequently influenced. The structure heredity of Al Sc master alloy was proved to be existed, and not influenced by prolonging insulation time and sufficient stirring. Unlabelled Image [ABSTRACT FROM AUTHOR]

• The isothermal reaction kinetics of ZnFe 2 O 4 in a CO−CO 2 -Ar mixture were studied. • The CO intensity impacts reaction rate more significantly than CO concentration. • The nucleation of ZnO is determined as the rate-controlling step. • The migration of Zn2+ together with O2− causes the slow nucleation of zinc oxide. The isothermal kinetics of zinc ferrite in a COCO 2 -Ar atmosphere were investigated by using thermogravimetric analysis (TGA). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were applied in studying the mechanism of reduction roasting. Linear-fitting of the measured data indicates that the growth of nuclei model is the kinetic model, and the overall E a was 72.75 kJ/mol; the kinetic equation was derived as follows: [ − ln (1 − α) ] 3 2 = 3.1054 × 10 6 ⋅ P CO 0.766 ⋅ V CO 1.135 ⋅ e − 72.75 × 10 3 R T ⋅ t. The CO intensity impacts the reaction rate more significantly than the CO concentration. The XRD and XPS results of the roasted products reveal that due to the migration of zinc ions together with oxygen ions during reductive roasting, the generation of magnetite is much faster than zinc oxide, indicating that the nucleation of zinc oxide is the rate-determining step. [ABSTRACT FROM AUTHOR]

The hardening behavior of Al-0.25Sc and Al-0.25–0.12 (wt.%) alloys during isothermal annealing were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), and hardness measurements. The results show that Sc-containing aluminum alloy contained fine dispersion of spherical secondary Al 3 Sc particles, which developed during the annealing process. Al 3 (Sc, Zr) precipitates in the Al-0.25Sc-0.12Zr alloys are core-shell structure. Different isothermal annealing temperatures can lead to different strengthening effects on the alloys. Al-0.25Sc and Al-0.25Sc-0.12Zr alloys both exhibit obvious annealing hardening behavior, and the ternary Al-0.25Sc-0.12Zr alloy shows better thermal stability than Al-0.25Sc alloy. • The diffusion rate of Sc atoms is inhibited by Zr atoms, which can prevent the coarsening of Al 3 (Sc, Zr). • The hardness decrease in Al–Sc alloy is mainly caused by the coarsening of Al 3 Sc particle. • The radius of the Al 3 (Sc,Zr) particles can maintain their value when annealed at higher temperature (>340 °C) for longer time (∼24 h). [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Mg-Si alloy is studied based on diffusion mechanism. The quantity of low angle grain boundaries increases rapidly, accompanied by the formation of subgrains and recrystallization grains with the increase of strain. Dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) are the main softening mechanisms, of which the DRV is dominant. The kinetics of dynamic recrystallization (DRX) represented by Avrami relationship shows that the DRX volume fraction increases with increasing strain. Physical-based diffusion constitutive model is established to demonstrate the flow behavior of the alloy. The relationship between diffusion activation energy and deformation condition is analyzed, and the dependence of creep exponent on temperature and strain is discussed. The result shows that the model describes the flow stress accurately. Lattice diffusion is the main diffusion mechanism during hot deformation. The variation of creep exponent can be reflected by dislocation density when the deformation mechanism is controlled by dislocation motion. Dynamic precipitation and the impediment of dislocation motion can lead to high value of creep exponent of the alloy. Unlabelled Image • Three types of physical-based diffusion models are established to demonstrate the flow behavior of the alloy. • The main diffusion mechanism during hot deformation is determined by constitutive analyses. • The relationships between creep exponent, diffusion activation energy and deformation condition are discussed. • The microstructure evolution and the dynamic softening mechanisms are investigated during hot deformation. [ABSTRACT FROM AUTHOR]

• Brass and S textures lead to larger Schmid's factor in the rolling direction (L–T). • FCG resistance in L–T was increased by atypical fibrous structure. • The cold-rolled-annealed samples show higher strengths and FCG resistance. • The alloy shows low anisotropy of FCG behavior in the Paris region. The fatigue crack growth characteristics of an Al-5.8Mg-0.25Sc(-0.4Mn-0.1Zr) alloy were investigated with regard to the loading direction. The cold-rolled and annealed samples show lower crack growth rates than hot-rolled samples at the same values of stress intensity factor (ΔK). The rolling (L–T) and transverse (T–L) directions exhibit different fatigue crack growth rates at the initial stage and unstable stage, but present similar behavior in the Paris stage. Results reveal that the Brass and S textures in Al-5.8Mg-0.25Sc alloy can lead to larger Schmid's factor and higher resolved shear stress in the rolling direction than in the transverse direction when the same value of stress is applied to the alloy, so the strength in the rolling direction is relatively lower and the fatigue crack growth rate of it is relatively higher in the initial stage. While the resistance to fatigue crack growth in the rolling direction was also increased by an atypical fibrous structure, consequently, the balance between the resolved shear stress and the resistance against fatigue crack growth related to the alloy orientation results in a unique anisotropy of fatigue crack growth behavior of Al-5.8Mg-0.25Sc alloy in the Paris region. [ABSTRACT FROM AUTHOR]

The quench sensitivity of Al–Mg–Si–Mn–Cr alloy was studied through time-temperature-transformation (TTT) and time-temperature-property (TTP) curves. The high quench sensitive region ranges from 250 °C to 430 °C with nose temperature at about 350 °C, where the quenching rate is required to higher than 9 °C/s for avoiding the formation of quench-induced precipitates. B′(Al 3 Mg 9 Si 7) precipitates from the supersaturated solid solution, and gradually transforms to equilibrium β (Mg 2 Si) and excess Si phase with increasing isothermal time at 350 °C. The loss of the solute atoms in matrix results in the reduction of the aging hardening precipitation and the formation of the precipitate-free zones (PFZs) during artificial aging. The nucleation rate of the quench-induced precipitation is studied by nucleation theory, and the phase transformation kinetics is analyzed through Avrami equation. The Al(MnCrFe)Si dispersoids, (sub)grain boundaries and dislocations are the preferential heterogeneous nucleation sites for quench-induced precipitation. • The quench sensitivity of the alloy was studied by time-temperature-transformation and time-temperature-property curves. • The microstructure evolution of the quench-induced precipitate and its effect on mechanical properties were analyzed. • The nucleation rate and phase transformation kinetics of the precipitation were investigated. • The preferential heterogeneous nucleation site for quench-induced precipitation was discussed. [ABSTRACT FROM AUTHOR]

Sulfidation roasting followed by flotation is widely known as a possible generic technology for enriching valuable metals in low-grade Zn-Pb oxide ores. Zn 2 SiO 4 is the primary Zn phase in willemite. Zn 4 Si 2 O 7 (OH) 2 (H 2 O), the main Zn phase in hemimorphite, transforms into Zn 2 SiO 4 at temperatures above 600 °C. To enrich the Zn in willemite and hemimorphite, the Zn species should first be converted to ZnS. Therefore, a thorough understanding of the sulfidation reaction of Zn 2 SiO 4 during roasting with pyrite is of vital important. In this study, the sulfidation behavior and reaction mechanisms of a Zn 2 SiO 4 -pyrite roasting system were determined using HSC 5.0 software, TG-FTIR spectroscopy, XRD, XPS and SEM-EDS. The results indicate that the sulfidation process can be divided into three steps: the decomposition of pyrite and formation of a sulfur-rich environment, the sulfur-induced migration of O 2− and transformation of sulfur vapor, and the sulfidation reaction via oxygen-sulfur exchange. During the sulfidation roasting process, pyrite was converted to loose and porous Fe 3 O 4 , whereas Zn 2 SiO 4 was transformed into ZnS and SiO 2 in situ. These findings provide theoretical support for controlling the sulfidation roasting process of willemite and hemimorphite. [ABSTRACT FROM AUTHOR]

The existing form of Sc in Si-containing 6xxx-series Al alloys and its role in strength has always been controversial. In this study, isothermal section phase diagram of the Al-0.60 wt%Mg-Si-Sc system at 350 °C was calculated by CALPHAD method and Pandat software, and the results show that Sc exists in Al 3 Sc or V (AlSc 2 Si 2) phases, depending on the contents of Si and Sc. Subsequently, we designed a Al-0.60 Mg-0.75Si-0.05Sc (wt%) Melt Inert Gas (MIG) welded alloy, and investigated its microstructure and mechanical property by tensile tests and electron microscopy. HRTEM and STEM-EDS results show that, Sc exists in the form of core(Sc)-shell (Si) structured (Al, Si) 3 Sc transition phases with the size range of 60–80 nm in the fractured zone (heat affected zone, HAZ) of the welded joints, deriving from equilibrium phase diagram, V (AlSc 2 Si 2) theoretically. The HAZ of the Al-Mg-Si-Sc joint consists of partly recrystallized grains and strong rolling texture, different from the completely recrystallized and coarsened grains in the Al-Mg-Si joint. In addition, the (Al, Si) 3 Sc phases increase the density of β'′ aging strengthening phases and prevent them from coarsening under welding heat cycle. The above positive effects of (Al, Si) 3 Sc particles increase the yield strength, ultimate tensile strength and elongation of Al-Mg-Si welded joints by 31 MPa (20.6%), 41 MPa (21.2%) and 0.8% (12.9%), respectively. [Display omitted] • Clarify the existing form of Sc in metal-inert gas welded Al-Mg-Si alloys. • Investigate the thermal stability of (Al, Si) 3 Sc phases and their effects on microstructure under welding thermal cycle. • Quantify the role of Sc in strength of metal-inert gas welded Al-Mg-Si alloys. [ABSTRACT FROM AUTHOR]

Modified zero valent iron (ZVI) is obtained from commercial iron powder co-ground with manganese dioxide (MnO 2 ) in intensive mechanical stress. The result indicates that the modified ZVI is very effective in arsenic sludge stabilization with a declination of arsenic leaching contraction from 72.50 mg/L to 0.62 mg/L, much lower than that of ordinary ZVI (10.48 mg/L). The involved process, including mechanochemical activation, corrosion and arsenic adsorption, is characterized explicitly to verify the improved arsenic stabilization mechanism. It shows that the mechanically formed Fe-Mn binary oxides layer results in an intensive corrosion extent, generating a mass of corrosion products. Moreover, as the emergence of Mn will restrain the process of iron (hydr)oxides crystallization, the ultimate corrosion products of the modified ZVI predominates in amorphous iron (hydr)oxides, performing much better in arsenic absorption. According to the BCR analysis, unstable arsenic in sludge is easily transformed to residual fraction by the help of amorphous iron (hydr)oxides, resulting in a restrained environmental availability of arsenic sludge after the modified ZVI stabilization. [ABSTRACT FROM AUTHOR]

Corrosion behaviour of 2A97-T6 Al-Cu-Li alloy was investigated by anodic polarization, immersion test and quasi-in-situ analysis with corrosion morphology characterized by a range of electron microscopy techniques. It is revealed that selective dissolution of grain interior tends to occur in grains of high stored energies, resulting in corroded bands associated with dense precipitate bands in the alloy. The evolutions of corrosion morphology during immersion test and quasi-in-situ analysis are similar, which both exhibit well-defined crystallographic pits. By contrast, crystallographic feature was less evident for localized corrosion induced by anodic polarization, which may be associated with the extensive Cu re-distribution. • Corroded bands are confined within individual grains of high stored energies. • Corroded bands are related to precipitates. • Cu re-distribution promotes the localized corrosion development but compromises its crystallographic features. [ABSTRACT FROM AUTHOR]

Stress corrosion cracking (SCC) behavior and mechanism of a friction stir welded Al–Zn–Mg–Zr alloy with 0.25 wt.% Sc were investigated. Impurity intermetallics and primary Al 3 Sc x Zr 1− x particles both crack perpendicular to tensile direction, whereas anodic dissolution only occurs around the former, initiating SCC. During cracking propagation, both anodic dissolution and hydrogen embrittlement operate. The thermo-mechanically affected zone on advancing side adjacent to weld nugget zone is most susceptible to SCC, which can be ascribed to the enrichment of impurity intermetallics, continuously distributed grain boundary precipitates and its stronger galvanic coupling with weld nugget zone from their greater microstructure and micro-chemistry differences. [ABSTRACT FROM AUTHOR]

The non-superplastic Al–Zn–Mg alloy sheet produced by a simple traditional thermal–mechanical processing can achieve high superplasticity at the temperatures ranging from 450 to 500 °C and the strain rates ranging from 1 × 10 −3 to 1 × 10 −2 s −1 by low scandium additions in the presence of 0.10% Sc (wt.%). An elongation of 1050% is obtained at 500 °C and 5 × 10 −3 s −1 . Analyses on the superplastic data reveal that the average values of the strain rate sensitivity and the activation energy of the Al–Zn–Mg–Sc–Zr alloy are about 0.5 and 85 kJ/mol −1 , respectively. The microstructural results show that the studied alloy consists of 3.14 μm grains characterized by a high fraction of low angle grain boundaries and strong β-fiber rolling textures. During superplastic deformation, low angle grain boundaries gradually transfer into high angle grain boundaries to sustain grain boundary sliding, and the texture intensity diminishes. Besides, β-fiber rolling textures weaken and cube and random textures are dominant in the superplastic deformed alloy. Superior superplastic ductility of the Al–Zn–Mg–Sc–Zr alloy is ascribed to the coherent 10–20 nm Al 3 Sc x Zr 1− x particles that strongly retard recrystallization grain growth. Analyses of the superplastic data indicate that grain boundary sliding is the predominant deformation mechanism. [ABSTRACT FROM AUTHOR]

New aerospace high strength Al–Zn–Mg and Al–Zn–Mg–0.25Sc–0.10Zr (wt%) alloys were welded by tungsten inert gas (TIG) process using a new Al–6.0Mg–0.25Sc–0.10Zr (wt%) filler material, and friction stir welding (FSW) process, respectively. Mechanical property and microstructure of the welded joints were investigated comparatively by tensile tests and microscopy methods. The results show that Sc and Zr can improve the yield strength and ultimate tensile strength of Al–Zn–Mg alloy by 59 MPa (23.3%) and 16 MPa (4.0%) in TIG welded joints, and by 77 MPa (23.8%) and 54 MPa (11.9%) in FSW welded joints, respectively. The ultimate tensile strength and elongation of new Al–Zn–Mg–Sc–Zr alloy FSW welded joint are 506±4 MPa and 6.34±0.2%, respectively, showing superior post welded performance. Mechanical property of welded joint is mainly controlled by its “weakest microstructural zone”. TIG welded Al–Zn–Mg and Al–Zn–Mg–Sc–Zr alloys reinforced with weld bead both failed at fusion boundaries. Secondary Al 3 Sc x Zr 1− x particles originally present in parent alloy coarsen during TIG welding process, but they can restrain the grain growth and recrystallization here, thus improving welding performance. For two FSW welded joints, fracture occurred in weld nugget zone. Secondary Al 3 Sc x Zr 1− x nano-particles almost can keep unchangeable size (20–40 nm) across the entire FSW welded joint, and thus provide effective Orowan strengthening, grain boundary strengthening and substructure strengthening to strengthen FSW joints. The positive effect from Sc and Zr additions into base metals can be better preserved by FSW process than by TIG welding process. [ABSTRACT FROM AUTHOR]

Corrosion behaviour, residual stress, intermetallics and microstructure of friction stir welded aerospace Al–Zn–Mg and Al–Zn–Mg–0.10Sc–0.10Zr (wt.%) alloys were investigated comparatively and in detail. The thermo-mechanically affected zones adjacent to weld nugget are most susceptible to corrosion in two weld joints. In addition to the enrichment of coarse Si and Fe intermetallics, wide precipitate free zones (in Al–Zn–Mg weld joint) and high tensile residual stress are the key factors. Secondary Al 3 Sc x Zr 1− x nanoparticles can effectively improve stress corrosion cracking resistance and decrease exfoliation corrosion rates of Al–Zn–Mg weld joints by restraining the formation of precipitate free zones and refining grains. [ABSTRACT FROM AUTHOR]

• The non-isothermal formation kinetics of ZnFe 2 O 4 by ZnO and Fe 2 O 3 was studied. • The E a increased from 9.76 kJ mol−1 to 290.70 kJ mol−1 in the overall reaction. • The reaction mechanism changed from diffusion to crystallization of ZnFe 2 O 4. • Zn ions will preferentially diffuse to Fe 2 O 3 matrix in diffusion process. The formation mechanism of zinc ferrite during the heat treatment of zinc oxide and ferric oxide was investigated. It is revealed in the kinetic study that the formation of zinc ferrite is an endothermic reaction with an apparent activation energy E a that increases from 9.76 kJ mol−1 to 290.70 kJ mol−1. This variation of E a indicates that the reaction between ZnO and Fe 2 O 3 is a multistep reaction, which could be described by the D3 (3D Jander Equation) - An (n-dimension Avrami-Erofeev Equation) model. The first step is the diffusion of the reactant, corresponding to the stage when the E a is low. As the reaction proceeds, the rate-determining process switches to the crystallization of zinc ferrite, which is reflected by a simultaneous increase in the XRD peak height and E a. The results of first-princeples calculations show that zinc oxide preferentially diffuses to the iron oxide matrix, and the inverse process causes an increase in the system energy. These results provide great insight into the kinetic basis for understanding the formation of spinel ferrites via a high-temperature solid-state reaction. [ABSTRACT FROM AUTHOR]