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Over the past few years, researchers have developed the alloy Al-Mg-Zn(-Cu), a new aluminum alloy based on the technique of 'crossover alloying'. The main strengthening phase of this novel alloy is T-Mg32(Al, X)49(X is Zn and Cu) after ageing and hardening. This alloy system has exceptional strength and corrosion resistance, making it a promising candidate for applications in fields like automotive, marine, aerospace, and many others. In this work, the research progress of the Al-Mg-Zn(-Cu) alloy based on microstructure control, composition, design, and properties has been reviewed. Future directions for the research of this alloy are highlighted, too. In this work, crossover alloys are presented as a potential novel class of Al alloys implicating a pioneering design approach, with particular emphasis on the aeronautical and aerospace field in which radiation resistance results are one hundred times higher than traditional precipitation hardening alloys. [ABSTRACT FROM AUTHOR]

Over the past few years, researchers have developed the alloy Al-Mg-Zn(-Cu), a new aluminum alloy based on the technique of ‘crossover alloying’. The main strengthening phase of this novel alloy is T-Mg32(Al, X)49(X is Zn and Cu) after ageing and hardening. This alloy system has exceptional strength and corrosion resistance, making it a promising candidate for applications in fields like automotive, marine, aerospace, and many others. In this work, the research progress of the Al-Mg-Zn(-Cu) alloy based on microstructure control, composition, design, and properties has been reviewed. Future directions for the research of this alloy are highlighted, too. In this work, crossover alloys are presented as a potential novel class of Al alloys implicating a pioneering design approach, with particular emphasis on the aeronautical and aerospace field in which radiation resistance results are one hundred times higher than traditional precipitation hardening alloys.

Aluminium–Silicon (Al-Si) eutectic alloy matrix composites are widely used in engineering application. However, it is a well-known fact that this material is not heat-treatable. In order to take advantage of the improvement in the mechanical properties due to the heat treatment, it is essential to find a way to make the Al-Si composite heat treatable. The dissolution of magnesium in the matrix, makes the composite age-hardenable, showing improvements in hardness and tensile strength properties according to changes in aging kinetics. This study analyses the peak aging kinetics on the hardness-related property improvement according to the magnesium dissolution content in the matrix. Hence, this research focuses on the role of aging treatment on the mechanical properties, especially the hardness of stir-cast Al-Si matrix Silicon Carbide (SiC) composites with up to 1.5 wt. % Mg intentionally dissolved in base alloy. Two aging temperatures (100 and 200 °C) were pitched into the target peak hardness and peak-aged condition. A minor quantity of Mg dissolution in the Al-Si matrix SiC composite has resulted in the improvement of hardness up to 24%, and age-hardening conditions contributeed up to a 40% increase in peak hardness. Similarly, the peak aged condition tensile strength shows an increase of up to 45% during age hardening compared to the Mg-free as-cast composite.

In the present research, the effect of thixoforming and age-hardening heat treatment on the microstructure and mechanical properties of un-modified and modified Al–20%Mg2Si composites produced through the strain-induced melt activation (SIMA) process has been investigated. This method showed promising potential for manufacturing the ideal microstructure, achieving globular grains, and enhancing mechanical properties. Quantitative analysis has revealed that adjusting the semi-solid heat treatment parameters to a temperature of 570 °C and a holding time of 25 min optimizes the globular α-Al grains and Mg2Si particles, achieving the size of 20.62 μm and 66.71 μm and the shape factor of 0.81 and 0.83 for Mg2Si particles and α-Al grains, respectively. The yield strength of the modified Al–20%Mg2Si composite increased by 23.67% and the ultimate tensile strength increased by 21.20%, compared to the un-modified specimen. Both composites underwent the thixoforming process, illustrating the ultimate tensile strength and elongation of 93.68 MPa and 4.32% for the original composite and 138.86 MPa and 7.29% for the modified composite. The modified Al–20%Mg2Si composite was subjected to the effective combination of thixoforming and age-hardening. According to the tensile test results, the yield strength, ultimate tensile strength, elongation, and toughness raised by 138.72%, 140.92%, 267.70%, and 471.12%, respectively, compared to the as-cast specimen. Moreover, its impressive hardness of 125.1HB contributes to its overall performance.

The effects of P addition on the microstructure and properties of a Cu-Ni-Ti alloy were investigated. The relationship between evolution of precipitates and hardness, electrical conductivity and softening temperature was established. The results showed that P addition increases the hardness and electrical conductivity, while also possessing good softening resistance. After 90% hot rolling and 500 °C aging, the Cu-Ni-Ti-P alloy reaches its maximum hardness and electrical conductivity of 165 HV and 57.2%IACS. Furthermore, the softening temperature of Cu-Ni-Ti-P alloy reaches 720 °C. The addition of P promotes the precipitation of Ni atoms from the Cu matrix, reduces the concentration of solute atoms, and as a result, increases the electrical conductivity of the alloy. Furthermore, the formation of the Ni _3 P phase further enhances the hardness of the alloy. The P solute atoms dissolved in the matrix and the nano-scale Ni _3 P phase form, which may be one reason for the increase in hardness due to precipitation strengthening.

Microalloying is an effective method to improve the mechanical properties of 6063 Al–Mg–Si alloy. Here, in this work, the effects of trace Cu (0.14 wt.%) and Cr (0.10 wt.%.) additions on the microstructure and mechanical properties of 6063 Al–Mg–Si alloy were studied. The results show that the additions of two elements can cause significant age-hardening effects, and the yield and tensile strengths of the alloys are significantly increased after T6 heat treatment. Further, it is found that the Cu and Cr additions show different strengthening mechanisms in the alloy. Cu addition leads to a finer and denser distribution of the main strengthening phases in the peak aging of the alloy, as well as a large number density of the precipitated phases, resulting in an increase in the dislocation density of the alloy during strain and hindering the dislocation movement. However, Cr addition acts as an inhibitor of grain growth and results in grain refinement, which also increases the hindrance of dislocation movement during the plastic deformation of the alloy, resulting in an increase in the dislocation density, thereby strengthening the alloy. [ABSTRACT FROM AUTHOR]

Al-based foams have drawn increasing attention from industry due to their integration of structure and functional properties. However, large-sized Al-based foams still cannot be homogeneously strengthened by long-time aging due to their low thermal conductivity. In this study, we proposed an age-hardening approach that was applied in large-sized Al-0.16Sc-0.17Zr (wt.%) foams via micro-alloying with Zr and Ti compared with Al-0.21Sc foams; it not only achieved homogeneous strength by long-term aging but also reduced the cost of the alloy by substituting Zr and Ti for the more expensive Sc content. The results show that the Al3(Sc, Zr, Ti) phase with a core–shell structure as a crucial precipitation strengthening phase by micro-alloying with Zr and Ti was less prone to coarsening after a prolonged aging heat treatment. Therefore, the yielding strength of Al-Sc foam micro-alloying with Zr and Ti remained almost unchanged after a maximum aging time of 1440 h due to less coarsening precipitate, which is consistent with the results of mechanical experiments. These findings provide a new way for the heat treatment strengthening of large-sized Al-based foams, thus promoting their industrial applications. [ABSTRACT FROM AUTHOR]

Aluminium–Silicon (Al-Si) eutectic alloy matrix composites are widely used in engineering application. However, it is a well-known fact that this material is not heat-treatable. In order to take advantage of the improvement in the mechanical properties due to the heat treatment, it is essential to find a way to make the Al-Si composite heat treatable. The dissolution of magnesium in the matrix, makes the composite age-hardenable, showing improvements in hardness and tensile strength properties according to changes in aging kinetics. This study analyses the peak aging kinetics on the hardness-related property improvement according to the magnesium dissolution content in the matrix. Hence, this research focuses on the role of aging treatment on the mechanical properties, especially the hardness of stir-cast Al-Si matrix Silicon Carbide (SiC) composites with up to 1.5 wt. % Mg intentionally dissolved in base alloy. Two aging temperatures (100 and 200 °C) were pitched into the target peak hardness and peak-aged condition. A minor quantity of Mg dissolution in the Al-Si matrix SiC composite has resulted in the improvement of hardness up to 24%, and age-hardening conditions contributeed up to a 40% increase in peak hardness. Similarly, the peak aged condition tensile strength shows an increase of up to 45% during age hardening compared to the Mg-free as-cast composite. [ABSTRACT FROM AUTHOR]

In recent years, wire-arc directed energy deposition (waDED), which is also commonly known as wire-arc additive manufacturing (WAAM), has emerged as a promising new fabrication technique for magnesium alloys. The major reason for this is the possibility of producing parts with a complex geometry as well as a fine-grained microstructure. While the process has been shown to be applicable for Mg-Al-Zn alloys, there is still a lack of knowledge in terms of the influence of the WAAM process on the age-hardening response. Consequently, this study deals with the aging response of a WAAM AZ91 alloy. In order to fully understand the mechanisms during aging, first, the as-built condition was analyzed by means of high-energy X-ray diffraction (HEXRD) and scanning electron microscopy. These investigations revealed a fine-grained, equiaxed microstructure with adjacent areas of alternating Al content. Subsequently, the difference between single- and double-step aging as well as conventional and direct aging was studied on the as-built WAAM AZ91 alloy for the first time. The aging response during the various heat treatments was monitored via in situ HEXRD experiments. Corroborating electron microscopy and hardness studies were conducted. The results showed that the application of a double-step aging heat treatment at 325 °C with pre-aging at 250 °C slightly improves the mechanical properties when compared to the single-step heat treatment at 325 °C. However, the hardness decreases considerably after the pre-aging step. Thus, aging at lower temperatures is preferable within the investigated temperature range of 250-325 °C. Moreover, no significant difference between the conventionally aged and directly aged samples was found. Lastly, the specimens showed enhanced precipitation kinetics during aging as compared to cast samples. This could be attributed to a higher amount of nucleation sites and the particular temperature profile of the solution heat treatment. [ABSTRACT FROM AUTHOR]

Metal alloys with enhanced mechanical properties are in considerable demand in various industries. Thus, this study focused on the development of nanosized precipitates in Fe71.25(CoCrMnNi)23.75Cu3Al2 maraging medium-entropy alloy (MEA). The Fe-based alloying design in the MEA samples initially formed a body-centered cubic (BCC) lath martensite structure. After a subsequent annealing process at 450 °C for varying durations (1, 3, 5, and 7 h), nanosized precipitates (B2 intermetallic) enriched with Cu and with a diameter of approximately 5 nm formed, significantly increasing the hardness of the alloy. The highest Vickers microhardness of 597 HV, along with compressive yield strength and ultimate compressive strength of 2079 MPa and 2843 MPa, respectively, was achieved for the Aged_7h sample. Therefore, the BCC lath martensite structure with B2 intermetallics leads to remarkable mechanical properties. [ABSTRACT FROM AUTHOR]

It is well known that long time natural aging (NA) after quenching from solution treatment will significantly reduce the precipitation hardening kinetics and peak hardness of most 6xxx aluminum alloys during later artificial aging (AA). Here we demonstrate an effective strategy to accelerate precipitation hardening, taking advantage of NA. It is found that by a short time pre-aging (PA) at AA temperature, NA for up to 1 year can reduce the time to peak strength in a 6082 alloy during later AA. A simultaneous increase in yield strength and uniform elongation at peak-aged condition can be achieved as a result of finer and denser age-hardening precipitates than those formed by direct AA treatment. Quantitative characterization of the precipitate microstructure by annular dark field scanning transmission electron microscopy (ADF-STEM) and atom probe tomography (APT) reveals that PA generates a small fraction of fine β″ needle precipitates composed of 6–9 β″-eyes and a substantially high density of GP-zones composed of 3–5 β″-eyes, which are stable at room temperature and can grow easily into β″ upon AA. During NA after PA, more GP-zones with at least 2 β″-eyes form while the larger GP-zones inherited from PA grow further, both of which can act as the precursors of β″ precipitates during later AA. [Display omitted] [ABSTRACT FROM AUTHOR]

This study aims to explore the effects of age-hardened traces, magnesium (Mg) dissolution, and silicon carbide (SiC) reinforcement on the wear properties of eutectic aluminum-silicon (Al-Si) matrix composites, focusing on optimizing their performance for industrial applications. A systematic investigation was conducted using a full factorial experimental design, with analysis of variance (ANOVA) performed through Minitab software to quantify the individual and interactive effects of these factors on the wear rate and coefficient of friction (COF). The results demonstrated that age-hardened traces significantly enhance wear resistance by promoting the formation of finely dispersed hardening precipitates at moderate ageing temperatures, while over-ageing negatively impacts performance due to precipitate coarsening. SiC reinforcement emerged as a key factor in improving wear resistance, attributed to its high hardness and superior abrasion resistance. The role of Mg dissolution was found to be multifaceted, contributing to solid solution strengthening and grain refinement but also interacting with other variables in complex ways. The study concludes that the optimal combination of 1.5% Mg, 4% SiC, and a peak ageing temperature of 100 °C achieves the best balance between wear resistance and frictional performance. These findings offer valuable insights into the design of high-performance Al-Si composites, highlighting the importance of microstructural control to meet the demands of advanced engineering applications.

Microstructure evolution and mechanical properties of the as-drawn dilute Mg-0.8Al-0.1Ca-0.6Mn (wt. %) alloy wires during annealing and peak-aging treatment were investigated in this paper. The results show that the high density of nano-sized Al–Mn precipitates strongly hindered grain boundary migration to restrict grain growth during annealing under 300 °C and 400 °C, while grain growth was obvious and the uniformity of recrystallization grain size increased due to partial dissolution of Al–Mn precipitates at 500 °C. In addition, there was a growth preference in grains with (0001) orientation, which was closely associated with the texture changes. The alloy annealed at 500 °C for 10min exhibits remarkable age-hardening response and both the tensile yield strength and elongation to failure were improved simultaneously after peak-aging treatment, which was mainly attributed to the monolayered Guinier-Preston (G.P.) zones and planar Al2Ca precipitates.

An age-hardening nitriding gear steel 20CrNi3Mn2Al and its deep case plasma nitriding technology are developed to meet the requirements of large heavy-duty and high-speed gears.The hardness of the material in air-cooled solid solution state is 283~332 HBW， which can ensure good machinability. After the treatment of using 520~540 ℃ variable temperature deep case plasma nitriding process，the steel can obtain high surface hardness，thin compound layer and gentle hardness gradient. The hardness is higher than 900 HV at 0.1 mm below the surface and more than 600 HV at 0.4 mm below the surface； the nitriding depth is deeper than 0.6 mm and the substrate hardness rises to 400~450 HV. It can be used to manufacture gears of heavy load，high speed and high precision， which can partially replace the carburized gears， and therefore leave out the carburizing and oil quenching process， simplify the technology and reduce the gear distortion.

This research attempts to evaluate the effects of age-hardening on the mechanical behavior of aluminum (6063) alloy reinforced with alumina (Al2O3) particles. Aluminum (6063)/Al2O3 composites containing 0, 5, 7, 9 and 10 wt% Al2O3 particles respectively were fabricated using double stir casting technique and representative samples from each composition were subjected to age-hardening treatment at 180 °C for 60 min, 120 min and 180 min respectively. The microstructures were evaluated using SEM while fracture toughness and tensile properties were used to evaluate the mechanical behavior of both the as-cast composites and their age-hardened counterparts. The microstructure evaluation reveals formation of coherent precipitates of Mg2Si evenly distributed in the age-hardened composites. Significant improvement in tensile strength values of 129.8, 88.6, 90.6, 137.9 and 170.6 MPa were obtained for the age-hardened composites compared to their as-cast composites with 42.2, 72.9, 81.2, 80.84 and 71.5 MPa across the series respectively. Similar trend was observed for fracture toughness with KIC values of 7.5, 5.8, 4.5, 7.8 and 9.6 MPam1/2 for age-hardened composites compared with 4.68, 4.64, 4.07, 4.06 and 3.59 MPam1/2 obtained for their as-cast composites. Age-hardening time of 180 min impart better tensile strength and fracture toughness.

Modern industrial development has put forward higher demands on the performance of metallic structural materials, especially in terms of light weight, high strength and corrosion resistance. All of these characteristics are of particular importance in transportation fields. As one of the most representative structural materials, aluminum and alloys have exhibited significant advantages in light weight. Most of the alloys are prominently featured in one specific aspect. The overall performance still needs to be improved. In recent years, researchers have developed Al-Mg-Zn(-Cu) alloy, a new wrought aluminum alloy, whose design strategy is known as "crossover alloying". This novel alloy is an age-hardened Al-Mg alloy with a T-Mg32(Al, X)49 (X is Zn, Cu) phase as the main strengthening phase. This system of alloys exhibits excellent properties in terms of strength and corrosion resistance, which makes it promising for applications in automotive, marine, aerospace and other fields. This paper summarizes the research progress of Al-Mg-Zn(-Cu) alloy, and analyzes the basic methods of microstructural control in terms of composition design and property research. Finally, the future directions of this alloy are proposed. [ABSTRACT FROM AUTHOR]

A growing demand for resources has led to the expansion of agricultural areas worldwide. However, land conversion associated with poor soil management might lead to soil physical degradation. We investigated the effects of land conversion on soil physical properties in the Brazilian Cerrado region, under native Cerrado vegetation (NV)—pasture (PA) and NV—cropland (CL) conversion scenarios. Soil physical properties related to compaction, pore size distribution, and structure stability were assessed up to a 30 cm depth. Additionally, carbon levels of soil organic matter fractions (particulate and mineral-associated organic matter) were determined. Our results indicate that the compaction process equivalently reduced the soil porosity in PA and CL. However, soil penetration resistance was higher in PA (~2.5 MPa) than in CL (~1.5 MPa), as well as the stable mean weight diameter of soil aggregates. The highest total and labile organic carbon levels were observed in CL, while the lowest levels of total and labile organic carbon occurred in PA (smaller than in CL). These results suggest that the higher structural stability found in PA was mediated by the predominance of stabilized carbon (a decrease in the proportion of soil labile carbon), causing the gaining of soil strength under negligible soil volume variation (in comparison with CL). Our results suggest that the reduction in the soil porosity by compaction due to PA and CL uses can equivalently reduce macropore space and soil hydraulic functioning, and that soil carbon quality alterations (i.e., labile vs. stabilized fractions) are responsible for the gain in soil strength in long-term degraded PA areas. Future research should focus on understanding the magnitude in which soil organic matter controls soil physical attributes, such as soil strength in these expansion areas, and whether this gain in soil strength limits plant development and compromises productivity in the long term. [ABSTRACT FROM AUTHOR]

The age-hardening behavior of the Fe-Ni-based alloy HR6W without carbon was investigated at temperatures between 973 and 1173K for a maximum of 3000 h to clearly identify the nose temperature of the Fe2W Laves phase. The microstructure observation was carried out for the aged alloys using field-emission scanning electron microscopy. One-step increase of hardness was detected for the alloy, which corresponds to the precipitation of Fe2W phase. It was found that the Fe2W phase precipitates with a flake-like morphology within γ grain interior and with a granular morphology at grain boundaries. The TTP (time-temperature-precipitation) diagram for the alloy is established based on the results of hardness measurements and microstructure observations, and the C curve representing the time required to initiate precipitation of the Fe2W Laves phase within γ grain interior was determined. The nose temperature of the C curve was identified as 1100 K, and the precipitation starts at 20 h at the nose temperature. The precipitation of the Fe2W phase at grain boundaries occurs for one order of magnitude earlier than that within γ grain interior at temperatures below 1100 K. [ABSTRACT FROM AUTHOR]

2219Al alloys microalloyed with varying Cd contents were processed by casting technique. Differential scanning calorimetry (DSC) was performed from 323 to 823 K at four different heating rates of 283, 289, 293 and 298 K min−1, to investigate the precipitation kinetics of the alloys. The heating cycle of DSC curves exhibited an endothermic peak in the intermediate temperature range from 603 to 713 K corresponding to the precipitation reaction, whereas an endothermic drift at elevated temperatures representing melting of the alloy phases. All the peak temperatures increased with an increase in heating rate, indicating the precipitation reaction to be kinetically controlled. A new methodology was proposed to model the kinetic rate equation, governing the endothermic precipitation peaks. Activation energy and related kinetic parameters were evaluated for the alloys, and the influence of Cd additions was investigated. Activation energy was observed to decrease by around 8.3%, due to microalloying with 0.06 mass% of Cd, thus kinetically favouring the precipitation reaction. Functional forms of mole fraction transformed were optimized, so that the present model of rate equation may achieve a proper fit with the experimental results of the corresponding reaction peaks. The transformation rate predicted from the rate equation and the estimated kinetic parameters, was successfully compared with the experimental data with fairly good accuracy. Such correlation with the experimental results validates the adapted analytical procedure, establishes the confidence and prediction capability of the present kinetic model and the accuracy of the kinetic parameters evaluated. X-ray diffraction (XRD) studies were resorted on the age-hardened alloys, to identify the possible precipitating phase(s). XRD patterns indicated the precipitation of θ-phase (CuAl2) within the Al matrix, which controlled the strengthening mechanism. The DSC and XRD results were further supported with the microstructural characterization of morphology and composition of different phases, as observed under SEM and EDS analysis. Trace contents of Cd exhibited to have significant potential to control the precipitation kinetics, activation energy, precipitating phases and respective microstructural evolution of the investigated 2219Al alloy system, during age-hardening treatment. [ABSTRACT FROM AUTHOR]

In many industrial Al-Mg-Si alloys, natural aging (NA) has a detrimental effect on the age-hardening response during artificial aging (AA), due to the formation of unfavorable nanometer-sized solute clusters during NA. In this work, we systematically studied the atomic structures of solute clusters formed in a dilute 6060 alloy and a more concentrated 6082 alloy after 1-year NA and their influences on the age hardening behavior during the following AA. In 6060, it was found that NA promotes the formation of high-density solute clusters in the form of GP-zones composed of 1–3 β″-eyes, which can act as precursors of β″ precipitates, enhancing the age-hardening kinetics during AA. In contrast, most solute clusters in 6082 after 1-year NA are 1β″-eye, binocular and square GP-zones, while GP-zones containing multiple β″-eyes are rare. As a result, NA has a strong negative effect on the age-hardening response during AA and the peak-aged strength. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of Ca addition on the age hardening response and precipitation behavior of a Mg-7Y-0.5Zr (wt%) alloy during isothermal aging at 350 ℃ has been studied by hardness test and high-angle annular dark-field scanning transmission electron microscopy. The addition of 0.6 wt% Ca can effectively enhance the age hardening response of Mg-7Y-0.5Zr alloy at 350 ℃, and the enhanced hardness is mostly attributed to the uniform precipitation of a novel strengthening precipitate phase, designated β p. The β p phase forms as plates on { 10 1 ̅ 0 } α planes. It has a Cd 45 Sm 11 -type structure (space group F 4 ̅ 3m , lattice parameter a = 2.24 nm) and a composition of Mg 5 Y 0.8 Ca 0.2. Its orientation relationship with the α-Mg matrix phase is such that [ 1 ̅ 11 ] β p // [2 1 ̅ 1 ̅ 0] α and (110) β p // (0001) α. After prolonged aging at 350 ℃, the metastable phase β p can transform in-situ to the equilibrium phase β-Mg 24 Y 5 with a cube-to-cube orientation relationship. The β p → β phase transformation is associated with the transition of constituent atomic clusters and the re-distribution of selected atoms within clusters. • The addition of 0.6 wt% Ca to Mg-7Y-0.5Zr alloy can enhance the age hardening response at 350 ℃. • A novel strengthening phase β p is observed in the peak-aged Mg-7Y-0.6Ca-0.5Zr alloy. • The β p phase transforms in-situ to the equilibrium phase β-Mg 24 Y 5 after prolonged aging. [ABSTRACT FROM AUTHOR]

In this work, the contrast seen in low-angle annular dark-field (LAADF) scanning transmission electron microscopy (STEM) of Guinier-Preston zones (GP-zones) in Al-Mg-Si alloys (6xxx) is discussed by STEM simulations, conventional STEM and 4D-STEM data. It is found that GP-zones of the 6xxx system can be experimentally imaged even with some elemental contrast when collecting primarily the elastically scattered electrons which fall within the zero-order Laue zone (ZOLZ). It is found that GP-zones give rise to contrast in LAADF-STEM primarily due to static atomic displacement which results in diffraction contrast, i.e. Huang scattering. As a result of lattice distortion from the GP-zones' short-range order, more electrons get elastically scattered within the ZOLZ and can be exploited by LAADF-STEM. Typical challenges which might arise when imaging with a LAADF setup compared to a high-angle annular dark-field setup are discussed, as well as, the limits of interpretability of using coherently scattered electrons are examined. It is found that the effects of contrast reversal and misalignment can be drastically reduced by collecting electrons with a small gap from the bright field disc and using detectors with reasonable collection widths, i.e. larger than 5 mrad. Furthermore, it is found that a reduction of the probe's semi-convergence angle results in a better contrast due to the possibility of collecting more electrons which scatter within the ZOLZ. Probes with semi-convergence angles of around 20 mrad produced the most optimal results. • Collecting primarily elastically scattered electrons allows to image GP-zones of the 6xxx system. • Elemental contrast is preserved within the elastically scattered electrons. • Primary source of contrast stems from lattice distortions introduced by the GP-zones' short-range order. • Challenges that arise when imaging through LAADF-STEM can be suppressed by collecting electrons with a small gap from the BF disc. • Probe with a 20 mrad semi-convergence angle produces the most optimal imaging conditions. [ABSTRACT FROM AUTHOR]

The precipitation and dissolution kinetics of cast and solutionized Al–6.2wt%Cu–0.6wt%Mg alloys microalloyed with varying contents of Sn was investigated. Differential scanning calorimetry (DSC) was performed from 50 to 550 °C at four different heating rates. Exothermic peak within intermediate temperature range of 200–300 °C of DSC heating cycle represented the precipitation reaction. Endothermic drift at elevated temperatures corresponded to melting of alloy phases. Peak temperatures increased with increase in heating rate, indicating precipitation reaction to be kinetically controlled. The kinetic rate equation governing exothermic precipitation peaks was modelled using a new analytical technique. Activation energy and kinetic parameters were determined for the alloys, and effect of Sn concentrations was investigated. Functional forms of mole fraction transformed were optimized. Predicted transformation rate calculated using the kinetic rate equation and evaluated kinetic parameters, was successfully compared with experimental data with fairly good accuracy. To identify possible precipitating crystalline phase(s), X-ray diffraction (XRD) analysis was performed on age-hardened alloys. DSC and XRD results were further corelated with microstructural characterization of morphology and composition of different phases, as studied by SEM and EDS analysis. Microalloying with Sn up to 0.06 wt% was observed to kinetically favor the precipitation reaction, as evident from increased growth in θ-crystal size, increased volume fraction of microstructural θ-phase, decrease in peak temperature and lower values of activation energy. Trace additions of Sn revealed considerable potential to control precipitation kinetics, activation energy, precipitating phases, and respective microstructural evolution of the investigated Al–Cu–Mg alloy system. [ABSTRACT FROM AUTHOR]

Fe‐based heat‐resistant A286 superalloy is an age‐hardened austenitic stainless steel. Age‐hardening is greatly affected by TiC particles and η‐Ni3Ti phases. Herein, the evolution of TiC and η (hcp‐Ni3Ti) precipitations is investigated in six different A286 alloys with simultaneous variations of C and Ti contents, such as 0.00C–2.38Ti, 0.02C–2.46Ti, 0.04C–2.54Ti, 0.05C–2.58Ti, 0.06C–2.62Ti, and 0.08C–2.69Ti wt%. During microstructure evolution from solutioning state (900 °C for 2 h) to aging state (720 °Cfor 16 h), nodular/needle‐like TiC (fcc) and platelet lamellar structures of eta (η (hcp‐Ni3Ti)) phases are observed in the austenitic matrix of superalloys. Statistical analysis of TiC and eta phases after microstructural examination indicates that mean size goes up to 3.3 and 6.8 μm2 in 0.08C–2.69Ti wt% alloy, respectively. Yield strength and ultimate tensile strength are increased from 350 to 510 MPa and 530 to 650 MPa as a result of the strengthening mechanism of TiC from 0.00C–2.38Ti to 0.08C–2.69Ti wt% alloys, respectively. However, precipitation of these phases leads to brittleness of the alloys and elongation decreases from 20% to 12% with the increment of these phases. The strengthening mechanism is explained by stress–strain curves and fracture topography. [ABSTRACT FROM AUTHOR]

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn 1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg51Zn20 phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg2Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′1 phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca 0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

The effect of the quenching rate after solution treatment on the residual stress and precipitation behavior of a high strength Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu plate is studied. The simulation results show decreasing temperature gradient in the plate with decreasing quenching rate, which leads to weakened inhomogeneous plastic deformation and decreased residual stress. No dynamic precipitation on the grain boundary happens after either cold water cooling or air cooling, however, air cooling leads to dynamic precipitation of Mg-Zn phase on Mn particles around which a low-density precipitate zone develops after aging treatment. Moreover, the fine and densely distributed Mg-Zn precipitates observed after aging treatment of the cold water cooled alloy are replaced by coarse precipitates with low density for the air cooled alloy. Both the low-density precipitate zone near Mn particles and the coarsening of precipitates are the source of the decrease in hardness and tensile properties of the air cooled alloy. The residual stress drops faster than the hardness with decreasing quenching rate, which makes it possible to lower the residual stress without sacrificing too much age-hardening ability of the alloy.

The microstructure evolution and age-hardening response for different Sm/Sn ratios (0–2.55, in wt.%) of Mg-Sn-Sm alloys were investigated. The second phase formation in as-cast alloys and the Mg3Sm precipitates formed in aged alloys were characterized using XRD, FESEM and HAADF-STEM with EDS techniques. Results indicate that the Sm/Sn ratio has a great influence on the phase constitution, α-Mg grain size and age-hardening response. With the increment of Sm/Sn ratio, Mg41Sm5 and thermally stable MgSnSm phases precipitate. When the Sm/Sn ratio is about 1.19, the secondary dendrite arm spacing of α-Mg grains significantly decreases. Furthermore, the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response, the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition (ageing at 220 °C for a short time of 4 h). This is attributed to the large volume fraction of needle-like Mg3Sm precipitates formed in the α-Mg matrix during ageing treatment, which results in a significant precipitation strengthening effect. [ABSTRACT FROM AUTHOR]

This paper is oriented to appraise high, intermediate, and low temperature related performance of elastomeric and plastomeric binders and mixtures in order to evaluate their characteristics at various levels of environmental and loading conditions. Artificial oxidative hardening of asphalt binders and mixes was performed in the laboratory using short- and long-term aging protocols.At the binder level, the elastomers (styrene-butadiene-styrene (SBS) and rubber) and plastomer (ethylene-vinyl acetate (EVA)) materials improved high and intermediate temperature performance indices (G*/sin(δ) and G*.sin(δ), respectively). Interestingly, the aged SBS/bitumen blend had improved low-temperature cracking resistance compared to unaged counterpart. With the progress of oxidative hardening, the plastomer based binder did not show obvious change in the low-temperature cracking susceptibility compared to elastomer-modified binder. Seemingly, in the case of plastomer/bitumen blend, the propensity to low-temperature cracking is to a great extent controlled by the corresponding base bitumen. The plastomer based mixture had improved permanent deformation performance, whereas the elastomers afforded a tangible amelioration for the vulnerability to load and non-load associated cracking. The SBS based mixture showed highest low-temperature fracture energy compared to the EVA based mixture. Despite the determinantal effect of age-hardening to low and intermediate temperature-related cracking of mixes, the results confirmed that the elastomeric materials can retard the impact of aging level on the low temperature and fatigue cracking. Comparision of results was justified by the statistical analysis in order to determine the significance of bituminous material parameters on the measured properties. [ABSTRACT FROM AUTHOR]

The effect of heat treatment on the structural-phase state and hardness of small-sized castings made from the Cu-Cr-Al copper alloy obtained by casting in a water-cooled metal mold is studied. Using X-ray diffraction analysis, it was found that the castings consist of a matrix solid solution based on copper. The increased value of the crystal lattice parameter of the copper phase is associated with aluminum atoms dissolved in it. After a low-temperature (450 °C) tempering for 10 hours, the crystal lattice parameter of the matrix solid solution decreases, which is associated with the formation of the Al8Cr5 intermetallic compound on the surface of the casting.It is established that after heat treatment (hardening and tempering), the hardness of castings from the Cu-Cr-Al alloy increases by 1.5 times.

In the present study, the structural evolution of the precipitates in Mg-Gd-Y-Zr alloy is investigated by means of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The linearly aligned morphology of β ′ phases connected by bridging β M phase in one of the three equivalent crystal directions of [ 10 1 ¯ 0 ] is formed from defect-free randomly distributed β ′ phases. Considering the significant strengthening effect of β ′ precipitates, a novel perspective of investigating the induced strain field measured by geometric phase analysis (GPA) is conducted. The reducing value of the strain field accounts for a slight decrease in hardness after peak-ageing. Merging and rearrangement of β ′ precipitates are found to release the strain field. [ABSTRACT FROM AUTHOR]

Modern industrial development has put forward higher demands on the performance of metallic structural materials, especially in terms of light weight, high strength and corrosion resistance. All of these characteristics are of particular importance in transportation fields. As one of the most representative structural materials, aluminum and alloys have exhibited significant advantages in light weight. Most of the alloys are prominently featured in one specific aspect. The overall performance still needs to be improved. In recent years, researchers have developed Al-Mg-Zn(-Cu) alloy, a new wrought aluminum alloy, whose design strategy is known as “crossover alloying”. This novel alloy is an age-hardened Al-Mg alloy with a T-Mg32(Al, X)49 (X is Zn, Cu) phase as the main strengthening phase. This system of alloys exhibits excellent properties in terms of strength and corrosion resistance, which makes it promising for applications in automotive, marine, aerospace and other fields. This paper summarizes the research progress of Al-Mg-Zn(-Cu) alloy, and analyzes the basic methods of microstructural control in terms of composition design and property research. Finally, the future directions of this alloy are proposed.

This research work highlights the prediction of hardness behaviour of age-hardened LM4 and its composites fabricated using a two-stage stir casting method with TiB _2 and Si _3 N _4 . MATLAB - Artificial Neural Networks is used to predict the age-hardening behaviour of LM4 and its composites. Experiments (hardness and tensile tests) are conducted to collect data for training an ANN model as well as to investigate the effect of reinforcements and age-hardening treatment on LM4 and its composites. The results show that with an increment in the reinforcement wt%, there is an enhancement in hardness and ultimate tensile strength (UTS) values within the monolithic composites. As-cast hybrid composites display a 37 to 54% improvement in hardness compared to as-cast LM4. Heat-treated samples, specifically those treated with peak aging with MSHT and 100 °C aging, perform better than as-cast samples and other heat-treated samples in terms of UTS and hardness. Compared to as-cast LM4, MSHT, and 100 °C aged samples display an 85 to 202% increment in VHN. Hybrid composites perform better in terms of hardness, while composites with 3 wt% of TiB _2 (L3TB) perform better in terms of UTS, peak aged (MSHT and 100 °C aging) L3TB display 68% increment in UTS when compared to as-cast LM4. ANN model is developed and trained with five inputs (wt% of TiB _2 , wt% of Si _3 N _4 , type of solutionizing, aging temperature, and aging time) and one output (VHN) using different algorithms and a different number of hidden neurons to predict the age hardening behaviour of composites. Among them, Lavenberg-Marquardt (LM) training algorithm with normalized data and 30 hidden neurons performs well and shows a least average error of 1.588364. The confirmation test confirms that the trained ANN model can predict the output with an average %error of 0.14 using unseen data.

Well-designed β-Ti alloys exhibit a unique combination of low elastic modulus and high strength, making them promising candidates for the next generation of biocompatible implant materials. A recently PMDA-approved β-Ti alloy, stabilized by the addition of a β-phase stabilizing element (Nb), contains a small amount of Sn, which is not a β-stabilizer, to prevent the formation of brittle ω phase. Here, focusing on the Ti–V–Sn alloy system, we have elucidated two-fold roles of the neutral Sn addition in β-Ti alloys. First, although it cannot be completely suppressed by the β-stabilizing elements alone, co-alloying with Sn dramatically enhances the capability of preventing the local collapsing of the (111) β planes, the elementary process of β↔ω transformation, due to the emergence of many-body effects. Second, Sn atoms serve as anchors for adjacent β-stabilizing elements, preventing the phase separation at intermediate temperatures. These two synergistic effects lead to a comprehensive suppression of all modes of the ω phase transformation. [Display omitted] [ABSTRACT FROM AUTHOR]

Precipitation hardening and corrosion behavior of a friction stir welding (FSW) based on the aluminum alloy A6005 reinforced with TiB2 nanoparticles have been studied. Mechanical alloying (MA) and hot extrusion techniques have been employed as processing route followed by FSW. Samples characterization has been performed by DSC and TEM, and precipitation strengthening of the bulk samples and the FSW joint has been evaluated by micro-hardness tests after T6 thermal treatment. TEM characterization revealed the presence of Mg–Si hardening phases, mainly of β′ phase, and dispersoids of α-Al(FeMnCr)Si into the aluminum matrix. The results revealed that samples subjected to MA had less susceptibility to T6 thermal treatment and that the presence of nano-TiB2 reinforcement accelerates aging time. In addition, electrochemical tests based on polarization tests have been performed in 3.5% NaCl solution to assess the effect of FSW process on corrosion behavior. The FSW joint had worse corrosion behavior since the passive Al2O3 film was not generated on the weld zone. SEM–EDS analysis revealed that pits nucleated mainly in sites with a higher presence of Fe contaminant which acts cathodically with respect to the aluminum matrix, producing galvanic corrosion. [ABSTRACT FROM AUTHOR]

This study introduces research trends in the electronics materials, such as joining materials including high-temperature lead-free solder, sintered materials using metal particles and transient liquid phase (TLP) materials, and conductive materials such as aluminum and copper alloys. These studies include the content of the special issue published in Materials Transactions (Vol. 57, No. 6 and Vol. 60, No. 6) entitled Frontier Researches Related to Interconnection, Packaging and Microjoining Materials and Microprocessing for Such Materials. It also introduces interesting research contents, leading the development of next-generation electronics. [ABSTRACT FROM AUTHOR]

The FeCrAl-ODS alloy claddings were manufactured and Vickers hardness, ring tensile tests and transmission electron microscopy (TEM) observations of these claddings were performed to investigate the effects of thermal aging at 450°C for 5,000 and 15,000 h. The age-hardening of all FeCrAl-ODS alloy cladding was found. In addition, the significant increase in tensile strength was accompanied by much larger loss of ductility. It was suggested that this age-hardening behavior was attributed to the (Ti, Al)-enriched phase (¢A phase) and the ¡A phase precipitates (content of Al is <7 mass%). In comparison with FeCrAl-ODS alloys with almost same chemical compositions, there was significant agehardening in both alloys. However, the extrusion bar with no-recrystallized structures was keeping good ductility. It was suggested that this different behavior of reduction ductility was attributed to the effects of grain boundaries, dislocation densities and specimen preparation direction. [ABSTRACT FROM AUTHOR]

Non-spherical precipitates are the main strengthening source of the age-hardenable aluminum alloys. In the majority of the precipitation hardening models presented so far, the simple spherical shape has been assumed. Moreover, the models which considered the actual shape of the precipitates, are derived based on the simple assumption of steady-state diffusion problem solutions. In the present study, the classical Kampmann and Wagner numerical model of spherical precipitates is extended to model the kinetics of spheroidal shape precipitates evolution during the aging treatment of Al alloys. To do so, a new rate law is proposed using a similarity solution of the transient diffusion problem around the spheroidal precipitates, with different aspect ratios, and moving boundaries. Moreover, a modified age-hardening model which considered the effects of precipitate shape, size and volume fraction, is used to predict the variation of the alloy hardness during the aging process. The accuracy of the proposed model is shown by comparing the predicted features of precipitates, and hardness evolution with the published experimental data. Also, the validity of the existing approximate solutions for the aging problem is discussed. [ABSTRACT FROM AUTHOR]

The effect of Cu contents on nanocluster formation and the two-step aging behavior of Al–Mg–Si alloys was studied based on hardness, DSC and TEM results. The activation energies for the formation of Cluster (1) were 61.6, 70.3 and 92.9 kJ/mol for Cu-free, 1Cu (0.1 mass% Cu-added) and 3Cu (0.3 mass% Cu-added), respectively. It was confirmed that hardness increased slowly with increasing Cu content during natural aging for 3.6 ks. These results suggest that the formation kinetics of Cluster (1) decrease due to the vacancy trapping phenomenon, because of the strong interactions of the Cu-vacancies. Meanwhile, the effect of the formation of nanoclusters by Cu addition on the two-step aging behavior at 170 °C during natural aging was analyzed. Hardness at the initial stage of the two-step aging increased with increasing Cu contents. This was caused by the suppression of Cluster (1) formation during natural aging by the Cu additions. Based on TEM results, at the peak hardness of the two-step aging, the number density of precipitates was increased by increasing Cu contents, due to the suppression of nanocluster formation during natural aging. Nanocluster formation behavior by DSC, two-step aging behavior based on hardness results and precipitation observation at the peak hardness using TEM. Two types of nanoclusters were analyzed using DSC based on Gaussian function method in Al–Mg–Si alloys. The formation of nanoclusters is suppressed during natural aging by Cu additions. Also, the hardness is clearly increased by Cu addition at the initial stage of two-step aging at 170 °C after natural aging for 3.6 ks. Based on TEM results, the number density of precipitates was increased by increasing Cu contents at the peak hardness of the two-step aging due to the suppression of nanocluster formation during natural aging. [ABSTRACT FROM AUTHOR]

The effect of the quenching rate after solution treatment on the residual stress and precipitation behavior of a high strength Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu plate is studied. The simulation results show decreasing temperature gradient in the plate with decreasing quenching rate, which leads to weakened inhomogeneous plastic deformation and decreased residual stress. No dynamic precipitation on the grain boundary happens after either cold water cooling or air cooling, however, air cooling leads to dynamic precipitation of Mg-Zn phase on Mn particles around which a low-density precipitate zone develops after aging treatment. Moreover, the fine and densely distributed Mg-Zn precipitates observed after aging treatment of the cold water cooled alloy are replaced by coarse precipitates with low density for the air cooled alloy. Both the low-density precipitate zone near Mn particles and the coarsening of precipitates are the source of the decrease in hardness and tensile properties of the air cooled alloy. The residual stress drops faster than the hardness with decreasing quenching rate, which makes it possible to lower the residual stress without sacrificing too much age-hardening ability of the alloy. [ABSTRACT FROM AUTHOR]