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This paper investigated the effect of cooling rate after solution heat treatment and pre-aging at 303K after cooling on aging behavior of Al-- 6 mass%Zn--0.75 mass%Mg alloy to elucidate the aging behaviors and strengthening mechanism throughout aging heat treatment in the case of low cooling rate, such as furnace cooling, followed by solution heat treatment. Regardless the absence of pre-aging, the maximum hardness obtained in the materials with furnace cooling after solution treatment was almost the same as that of water-cooled and pre-aged materials during the same aging time. The result of microstructure observations using transmission electron microscope show that fine precipitates consisting of η phase have been formed in all peak-aged materials. [ABSTRACT FROM AUTHOR]

The weldability of an Al-11%Zn-3%Mg-1.4%Cu alloy by friction welding was investigated, and the effects of T6 treatment during and after welding on the microstructure and joint properties were clarified. Fine grains were formed at the interface of the as-welded joint and were coarsened by the T6 treatment. ηA phase was coarsened at the interface due to friction welding, on the other hand, fine ηA was precipitated again by T6 treatment after welding. The joint efficiency in tensile tests was 72% for the as-welded joint but recovered to 89% by T6 treatment after friction welding, and all fracture locations were near the interface layer. Tensile strength differed depending on whether the grain elongation direction was parallel or perpendicular to the tensile direction, suggesting that the grain shape near the interface was the cause of joint failure. [ABSTRACT FROM AUTHOR]

Aging behavior, cluster formation including near grain boundaries, and mechanical properties of Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy were investigated. The effect of Ag as a microalloying element was also clarified. The Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy showed higher aging hardening ability and shorter time to peak aging than the Al-5%Zn-2%Mg (-0.3%Ag) alloy from the early aging stage. The effect was greater with the addition of Ag, showing that the effects of solute content and micro-alloying elements on age hardening were recognized. 3DAP analysis revealed that Ag contributed significantly to the initial stage of cluster formation even when the solute elements were high. It was also found that clustering occurred in the vicinity of the grain boundary at a high density and fineness from the early stage of aging. By increasing the solute content of Zn and Mg to 11% and 3% respectively, the tensile strength of the alloy was over 800 MPa, and the addition of Ag further increased the strength. [ABSTRACT FROM AUTHOR]

The friction stir welding (FSW) process is a unique combination of deformation and high temperature, which provides opportunities to modify microstructures through the adjustment of the processing parameters and is an ideal way to join non-weldable aluminum alloys by avoiding the formation of a molten pool. The 7xxx series heat-treatable aluminum alloys are widely used in the aerospace field as high-performance structural materials. The microstructure evolution and mechanical performance of these alloys are affected by the effects of thermomechanical processing, which provides opportunities to optimize the material properties by controlling microstructural features such as intermetallic constituent particles, dispersoids and nanoscale precipitates. This paper focuses on the basic principles of the thermal and mechanical effects generated during FSW on the evolution of second-phase particles in different zones of the weld. [ABSTRACT FROM AUTHOR]

The internal microstructures of Ni–P-plated Al–Zn–Mg-based alloys were investigated using synchrotron X-ray computed tomography, together with various analytical methods for hydrogen detection. We clarified that hydrogen-induced pores were generated and segregated near the top and bottom surfaces of a rolled sheet of a commercial-purity Al–Zn–Mg-based alloy with Ni–P plating. In contrast, such segregation of hydrogen micropores was not observed in the high-purity-grade Al–Zn–Mg alloys with Ni–P plating. This result suggests that hydrogen enters the Ni–P plating layer during the plating operation and generates pores in the surface region owing to surface inclusions. Additionally, the hydrogen-induced defects deteriorated the tensile properties such as tensile strength and elongation of the commercial-purity Al–Zn–Mg-based alloys containing higher levels of impurities such as Fe and Si with Ni–P plating. [Display omitted] • Internal microstructures of Ni–P-plated Al–Zn–Mg-based alloys investigated. • Synchrotron X-ray computed tomography and hydrogen detection methods were employed. • H enters plating layer and generates surface micropores due to surface inclusions. • H-induced defects deteriorate the tensile properties of the plated pure alloy. [ABSTRACT FROM AUTHOR]

In Al-Zn-Mg alloy, hydrogen (H) leads remarkably to the degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for developing the high-strength Al-Zn-Mg alloy. Because intergranular fracture (IGF) is mainly observed when HE occurs in the alloy, we need to understand the initiation behavior of IGF in order to suppress HE. Heterogeneous distribution of stress, strain and H concentration usually influence the IGF initiation in polycrystalline material. In the present study, we investigated distribution of stress, strain, and H concentration in actual fractured regions by simulation employing a crystal plasticity finite element method and H diffusion analysis in a 3D image-based model, which was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. Combining the simulation and in-situ observation of the tensile test sample by X-ray CT, we examined the distribution of stress, strain, and H concentration in actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress normal to grain boundary induced by crystal plasticity dominates intergranular crack initiation. In contrast, accumulation of internal H due to the stress has little impact on crack initiation. [ABSTRACT FROM AUTHOR]

The nano-precipitates with minimal misfit strengthen Al–Zn–Mg alloys by impeding dislocation motion. However, grain boundary precipitates (GBPs) are known to have a completely incoherent relationship with the matrix, making them less effective in strengthening the alloys. Instead, GBPs are recognized for preoccupying elements such as Zn or Mg, thereby diminishing the quantity of nano-strengthening phases. GBPs significantly influence the deformation and fracture behaviors of Al–Zn–Mg alloys by accelerating stress localization and crack formation. In this study, we investigated how the accumulation of dislocations in the GBP areas leads to stress localization and subsequent cracking, using micropillar tests and crystal plasticity finite element method (CP-FEM) analysis. The dislocation pile-up in the GBPs causes stress localization around the grain boundaries, inducing crack initiation and leading to intergranular fracture. These findings enhance our understanding of the role of GBPs in the deformation and cracking of Al–Zn–Mg alloys and may pave the way for new concepts in managing GBPs.

In this study, the microstructural and mechanical properties of Al-Si3N4/TiB2 hybrid reinforced composites are examined. The aim is to investigate the impact of a novel combination of reinforcements (Si3N4/TiB2) on the mechanical behavior of hybrid metal matrix composites (HMMCs). The composites are produced by adding a fixed amount of Si3N4 (4 wt.%) and 2, 4, and 6 wt.% of TiB2, respectively, into molten AA7075 aluminum alloy using a liquid state stir casting process. The physical and mechanical properties of fabricated HMMCs are determined through the measurement of density, porosity, tensile strength, Brinell hardness, flexural, and impact strength. The microstructural study of HMMCs reveals a consistent distribution of microparticles within the matrix. Evidence of reinforcement particles in the HMMCs is confirmed through field emission scanning electron microscopy with energy-dispersive spectroscopy and X-ray diffraction analysis. The fabricated HMMCs with 4 wt.% Si3N4 and 6 wt.% TiB2 particulates demonstrated the greatest strength among others. The ultimate tensile strength, Brinell hardness, and flexural strength are improved by 59.36%, 95.59%, and 49.33%, respectively, compared to the base Al-Zn-Mg alloy. However, the increment in strength of HMMCs comes with the tradeoff of reduced ductility and impact resistance measured through the percentage elongation and energy absorbed by the samples. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of pre-precipitated η phases and Al3(Er, Zr) particles on the hot workability and recrystallization behavior of an Al–Zn–Mg–Er–Zr alloy. The optimal pre-precipitation heat treatment prior to hot deformation was obtained by heat treatment under different conditions combined with microstructure analysis. Subsequently, hot compression tests were conducted to establish the processing maps, and the influence of pre-precipitation on the microstructure and the hot workability under various thermal deformation conditions were analyzed. Furthermore, the effect of pre-precipitation of η phases and Al3(Er, Zr) particles on the recrystallization was studied. The results demonstrate that after the optimized pre-precipitation treatment, a multitude of Al3(Er, Zr) particles (∼10 nm) and η phases (∼1 μm) appeared in the alloy. Through this pre-precipitation treatment, the flow stress was significantly reduced, and the hot workability of the alloy was significantly enhanced, particularly at low temperatures and low deformation rates. Moreover, the pre-precipitated η phases facilitated recrystallization, refined grains and hence created a more homogeneous microstructure. Concurrently, during the recrystallization process, the precipitated Al3(Er, Zr) particles impeded grain boundary migration, and thus inhibited the growth of recrystallized grains, contributing to grain refinement.

In the present investigation an attempt was made to synthesize nano-SiC/BN-reinforced Al–Zn–Mg alloy composites by varying its weight percentage of SiC (2wt%, 4wt%, 6wt%) and maintaining 3wt% BN using the squeeze casting method and comparing it with as-cast aluminium alloy. SEM and ASTM standards are used to examine the morphology and mechanical behaviour of the synthesized aluminium alloy hybrid nanocomposite. Morphological study reveals that synthesized nanocomposites show uniform distribution of reinforcement particles without indication of residual pores. Due to the presence of Mg2Si interfaces and reduction in shrinkage effects during solidification, the density and porosity of hybrid intermixtures are increased to a minimum of 0.08% and reduced to 0.0026%. In comparison with as-cast Al–Zn–Mg alloy the hardness (28.37%), tensile strength (32.53), and yield strength (34.13%), flexural (31.25%), and impact strength (27.27%) significantly improved due to enhanced wettability between the intermixture and improved grain refinement. By increasing the proportion of strengthening particles, it was found that reducible dislocation motion was observed, resulting in an improved wear rate (26.82%) of the synthesized intermixture. [ABSTRACT FROM AUTHOR]

The surrogate-based microstructural optimization was applied to describe the relationship between local crystallographic microstructure and intergranular hydrogen embrittlement in an Al-Zn-Mg alloy. The support vector machine with an infill sampling criterion was used to realise high-accuracy optimisation with a limited size of data set. The methodology integrates thoroughgoing microstructural quantification, a couple of coarsening processes and the surrogate modelling. An objective function was defined together with 66 design parameters, which quantitatively express the size, shape, orientation and damage during specimen machining for surface grain boundaries and grains. The number of design parameters was then reduced from 66 to 3 during the two-step coarsening process. It has been clarified that intergranular crack initiation is described using the simple size of grains and grain boundaries together with grain boundary orientation with respect to the loading direction. It can be inferred that those design parameters are of crucial importance for crack initiation through the elevation in stress normal to grain boundaries. Correlation between the selected design parameters and crack initiation was rather weak compared to the past application of a similar technique to particle damage. The reason for this was discussed. The present approach offers a cost-efficient solution for the prevention of hydrogen embrittlement through 3D design of crystallographic microstructure, which cannot be obtained with the conventional approaches for developing materials. [ABSTRACT FROM AUTHOR]

Two arc welding modes of melt inert gas welding (MIG) and cold metal transition + pulse welding (CMT+P) were used to weld 20 mm thick 7A52 aluminum alloy. The effects of different arc welding modes on the microstructure and mechanical properties of welded joints were studied from the aspects of welding defects, grain size and precipitation. The results show that the two welded joints are well formed and have no obvious defects. The weld microstructure is as cast equiaxed dendrite. Strip or block iron rich impurity phases AlFeMn and Mg2Si and Al3Mg2 phase with non coherent relationship with the α(Al) matrix are found in the weld. However, the porosity of MIG welding weld area is 2.73%, while that of CMT+P welding weld area is only 0.64%. At the same time, the weld grain size is small, the width of heat affected zone is narrow and the grain boundary segregation is small in CMT+P mode, so the joint strength in CMT+P mode is higher, with about 289 MPa. The pull-down fracture of the two modes is characterized by ductile fracture with dimples as the main feature.

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Surrogate-based microstructural optimization was applied to model the relationship between local crystallographic microstructure and intergranular hydrogen embrittlement in an Al-Zn-Mg alloy, and a support vector machine with an infill sampling criterion was used to realise high-accuracy optimisation with a limited data set. This methodology integrates thoroughgoing microstructural quantification, two coarsening processes, and surrogate modelling. An objective function was defined together with 66 design parameters that quantitatively express size, shape, orientation and damage during specimen machining for surface grain boundaries and grains. The number of design parameters was then reduced from 66 to 3 during the two-step coarsening process. It has been clarified that intergranular crack initiation can be described using the simple size of grains and grain boundaries together with grain boundary orientation with respect to the loading direction. It can be inferred that these design parameters are of crucial importance in crack initiation through elevation in stress normal to grain boundaries. Correlation between the selected design parameters and crack initiation was somewhat weak compared to past applications of a similar technique to particle damage. The reason for this is discussed. The present approach offers a cost-efficient solution for the prevention of hydrogen embrittlement through 3D design of crystallographic microstructure that cannot be obtained using conventional strategies for developing materials. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Al-Zn-Mg alloys with different precipitate sizes were investigated to determine the influence of the precipitate size on the flow stress and dislocation density change during tensile deformation. The dislocation density was measured using in-situ X-ray diffraction at the SPring-8 synchrotron radiation facility with a time resolution of about 2 s. In region II with rapid dislocation multiplication, from under-aging to peak aging, the dislocation density increased with increasing aging time. Under over-aging conditions, the amount of dislocation multiplication in region II decreased with increasing aging time. Even in region III, the increase in dislocation density with plastic deformation was the largest for the peak aging conditions. However, the amount of work hardening was small and the contribution of dislocation hardening to the strength of the material was minimal. For over-aging conditions, the increase in dislocation density in region III was smaller than for the other regions, but the amount of work hardening was relatively large. It is considered that the influence of the dislocation density on work hardening is determined by the effectiveness of precipitates as obstacles to dislocation motion. [ABSTRACT FROM AUTHOR]

An Al–Zn–Mg-Sc-Zr alloy with high Zn was prepared to obtain ultra-high strength in the present study. The microstructure of the aged samples and the friction stir welding (FSW) joints were investigated by optical microscopy, electron backscatter diffraction and transmission electron microscopy. The mechanical properties were evaluated by microhardness and tensile tests. Results show that the peak microhardness of the aged Al–Zn–Mg-Sc-Zr alloy was ∼212.2 Hv. Strengths up to 697.2 MPa in the yield strength and 721.8 MPa in the ultimate tensile strength were obtained after ageing at 120 °C for 24 h, and the elongation was ∼9%. The ultra-high strength was mainly attributed to the precipitate strengthening from η′ and Al3ScxZr1-x precipitates, solid solution strengthening and fine grain strengthening. Soft regions with hardness of ∼122 Hv were developed near the interfaces between heat-affected zone and thermo-mechanically affected zone due to the coarsening and/or dissolution of strengthening precipitates. The joint coefficient was ∼69.5% for the Al–Zn–Mg-Sc-Zr alloy. Fine recrystallized grains with an average diameter of ∼1.8 μm were formed in the nugget zone (NZ), and these newly formed fine grains experienced further deformation and resulted in high fractions of substructure and deformed grain. The size and shape of Al3ScxZr1-x precipitates remain almost unchanged during ageing at 120 °C and the FSW processing. The existence of η phase in the NZ was associated with the Al3ScxZr1-x particles, indicating the heterogeneous precipitation of η precipitates on the Al3ScxZr1-x precipitates during FSW.

The existing phenomenological theories of plastic forming of sheet metal lack the predictability of the influences of dislocations and precipitates on viscoplastic damage in Al-Zn-Mg alloys. This study examines the evolution of grain size that occurs when the Al-Zn-Mg alloy undergoes a hot deformation process, specifically concentrating on dynamic recrystallization (DRX). The uniaxial tensile tests are conducted at deformation temperatures ranging from 350 to 450 °C and strain rates of 0.01–1 s−1. The intragranular and intergranular dislocation configurations and their interactions with dynamic precipitates are revealed by transmission electron microscopy (TEM). In addition, the MgZn2 phase induces microvoid formation. Subsequently, an improved multiscale viscoplastic constitutive model is established that emphasizes the effect of precipitates and dislocations on the evolution of microvoid-based damage. Using a calibrated and validated micromechanical model, the simulation of hot-formed U-shaped parts is conducted through finite element (FE) analysis. During the hot U-forming process, the formation of defects is expected to have an impact on both the distribution of thickness and the level of damage. In particular, the damage accumulation rate is influenced by temperature and strain rate, and local thinning is caused by the damage evolution of U-shaped parts. [ABSTRACT FROM AUTHOR]

The present work investigates the microstructural and mechanical properties of nano-Si3N4-BN hardened Al–Zn–Mg alloy hybrid nanocomposites synthesized by a vacuum-assisted stir casting process using different weight fractions. The microstructural analysis is performed using an optical microscope and the morphology studies were characterized using SEM analysis. The B117 salt spray test has been used to analyze the corrosion tests on hybrid nano composites. The microstructure evaluation revealed that nano-reinforcing particles are uniformly distributed in the matrix alloy without residual pores forming in the matrix alloy and shows the occurrence of intradendritic grains along the grain boundaries. Morphology analysis of synthesized Aluminium alloy hybrid nanocomposites illustrates that ceramic hard particles cannot be resolved and appear as fine globular species at high temperatures and its crystalline size of an average 44.9 nm has been observed. Owing to reduction in grain size and enhanced grain refinement the tensile and compressive strength of hybrid nano composites significantly increased in comparison with as cast Al–Zn–Mg alloy. The presence of Al2Cu forms as an intermetallic phase, impeding dislocation progression and it acts as corrosion resistant of developed hybrid nano composites.

Scandium addition to aluminum alloys has been evaluated at various research institutions, and it is known that the Al3Sc precipitates effectively increase their strengths. In this study, the effect of Sc addition on the strengths of two types of 7000 series aluminum alloys was investigated. As a result, the strength increased by the Sc addition to both types of alloys, but the increased amounts were limited to 1040 MPa. It was considered that because the strengthening effect by the n phase was sufficiently high, the precipitation strengthening by the dispersion of Al3(Sc1-xZrx) particles was relatively low in these alloys. [ABSTRACT FROM AUTHOR]

First principles calculations and scanning Kelvin probe force microscopy (SKPFM) were used to investigate the effect of elements migration of α-AlFeMnSi phase on micro-galvanic corrosion behavior of Al—Zn—Mg alloy. The simulation results showed that the average work function difference between the α-AlFeMnSi phase and Al matrix decreased from 0.232 to 0.065 eV due to the synchronous migration of elements Fe—Mn—Si. Specifically, as the elements Fe—Si migration during the extrusion process, the average Volta potential difference detected by SKPFM between the α-AlFeMnSi phase and Al matrix dropped down to 432.383 mV from 648.370 mV. Thus, the elements migration reduced the micro-galvanic corrosion sensitivity of Al—Zn—Mg alloy. To reach the calculated low micro-galvanic tendency between α-AlFeMnSi phase and Al matrix, the diffusion of Mn should be promoted during extruding process. [ABSTRACT FROM AUTHOR]

Recent studies have revealed that hydrogen embrittlement in AlZnMg alloys appears to be dominated by hydrogen partitioning to MgZn2 precipitates. A method has recently been proposed for reducing the hydrogen concentration at MgZn2 precipitates by adding specific intermetallic compound particles that have high hydrogen trap energy. In the present study, the effectiveness of Al7Cu2Fe particles on suppression of hydrogen embrittlement in Al-Zn-Mg-Cu alloys was evaluated using X-ray microtomography. Quasi-cleavage cracks were found to be initiated in regions where local volume fractions of the Al7Cu2Fe particles were relatively low. Hydrogen partitioning to the MgZn2 precipitate interface was suppressed, even in high hydrogen concentration material, by adding Al7Cu2Fe particles. However, the fractional area of the quasi-cleavage fracture in the material with high hydrogen concentration was higher due to insufficient hydrogen diffusion inside the Al7Cu2Fe particles and at the interface between the aluminum matrix and the particles. It appears that finely distributed small Al7Cu2Fe particles might effectively suppress hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) offers obvious advantages in the production of complex parts. However, the traditional 7xxx series aluminum alloy has a serious cracking tendency in the SLM process. Therefore, in order to analyze the microstructure and cracking mechanism, and obtain crack-free aluminum alloy fabricated by SLM, this paper studied the microstructure characteristics of as-deposited Al-6.2Zn-2Mg-xSc-xZr alloy with different Sc, Zr content, as well as the influence mechanism of Sc, Zr on cracking. The results show that with the increase of Sc and Zr content, the crack tendency and grain size decrease. When Sc and Zr content reach 0.6% and 0.36% respectively, cracks can no longer be observed in the as deposited alloy. The microstructure of the as deposited Al-6.2Zn-2Mg-0.6Sc-0.36Zr alloy consists of fine equiaxed and columnar crystals, in which Sc and Zr mainly exist in the aluminum matrix as solid solutions, and some exist in the form of Al3(Sc, Zr). The immediate reason for the absence of cracks is that the microstructure changes from coarse columnar grains to fine equiaxed-columnar grains when the content of Sc and Zr increases. The refined grain size may have the following beneficial effects: It helps with reducing the thickness of the liquid films. This will increase the tear sensitivity of the liquid film and the cracking tendency and therefore lowers the hot cracking tendency; And a refined grain size improves fracture roughness, leading to an enhanced cracking resistance. At the same time, the refinement of the grains will make the feeding channel of the grain boundary shorter and easy to feed, and the fine equiaxed grains can coordinate stress-strain during solidification more effectively than coarse columnar grains, which will decrease the cracking tendency. [ABSTRACT FROM AUTHOR]

In this study, the effects of different (online quenching and offline quenching) quenching methods and aging processes (T6 and T73) on the crashworthiness and microstructural evolution of three Al–Zn–Mg alloys (G1–G3) were studied by conducting tensile test and axial compression tests at room temperature, combined with optical metallography, electron back scattered diffraction, and transmission electron microscopy microstructural observations. The obtained results revealed that the crushing properties of three different Al–Zn–Mg alloys subjected to different quenching methods and aging processes were significantly different. Their crushing energy absorption of are ranked as follows: G1 > G3 > G2. The highest total energy absorption gap (between T6 and T73) is the G1 alloy, and the lowest one is the G3 alloy. The largest total energy absorption gap between the two quenching methods is the G3 alloy, and the smallest one is the G1 alloy. The G2 alloy with the largest total amount of Zn + Mg has the highest number density of matrix precipitates, the largest precipitate gap (between T6 and T73) and the smallest precipitate gap between the two quenching methods. The G3 alloy with the largest Zn/Mg ratio has the smallest number density of matrix precipitates, the minimum precipitation gap (between T6 and T73) and the maximum precipitation gap between the two quenching methods. The G1 alloy with the lowest Zn/Mg ratio has the smallest size of grain boundary precipitates and PFZ width, while their largest values are obtained for the G3 alloy with the maximum Zn/Mg ratio. As a crushing resistant structural material, the crushing properties is improved without reducing the strength. The ratio of Zn/Mg should be controlled within the range of 4.57–6.15, while the total amount of Zn + Mg should be controlled within the range of 6.18–7.01. [ABSTRACT FROM AUTHOR]

This study suggests a new way to modify the size and morphology of Al-Fe phases in modified AA 7075 by using an Fe-Mn solid solution powder as the precursor. When Fe and Mn are added in the form of a solid solution, the diffusion of Fe and Mn toward the Al is delayed, thus altering the chemical composition and morphology of the precipitates. The fine, spherical precipitates are found to provide a good balance between strength and ductility compared to the case where Fe and Mn are separately added.

In this study, the polymer replication method was applied to obtain metal foam from composite powders produced by the mechanical alloying by adding different amounts of B4C (5, 10, 15 wt.%) to the AA7075 aluminum alloy matrix. The corresponding AA7075 aluminum alloy and B4C powder ratios were mechanically mixed in a planetary ball mill for 300 min for the composite powder preparation. Afterward, the composite metal foam was produced from mechanically alloyed composite powders, with polyvinyl alcohol (PVA) as a binder, polycarboxylic acid as a dispersant, distilled water, and a polyurethane sponge template with a linear cell number of 25 PPI (Pores Per Inch). The effect of the amount of reinforcement on the microhardness of the composite metal foam was then analyzed. DTA/TG/DSC analyzes were performed on aluminum composite powders and polyurethane foam to determine the sintering temperature suitable for the composite foam and the combustion temperature of the polyurethane foam. Thermal treatment was carried out to strengthen the foams produced. To this end, the model material was removed from the structure, and then sintering was carried out at 650°C for 3 hours. The characterization and morphological analysis of the foams produced was carried out using the XRD and SEM/EDS methods. It was observed that apart from α-Al and B4C phases, secondary and tertiary Al3BC, AlB2, AlB12C2, and Al3B48C2 phases were formed as a result of the sintering process. The results of the EDS analysis showed the presence of elements O, except for elements Al, Zn, and Mg belonging to an AA7075 alloy and elements B and C belonging to the reinforcing element. Densities of composite metal foams produced with a solids content of 60% were measured between 0.12–0.15 g/cm3, and their porosity values were calculated between 90.4–95.5%. The study's findings allow stating that the increase in hardness was directly proportional to the rise in the amount of the reinforcing agent. The highest hardness was 28 HV in composite metallic foam with an additive of 15% B4C by weight. [ABSTRACT FROM AUTHOR]

The structural stabilities and thermal properties of η′ and η phase at high temperature and pressure were investigated via first principles calculations combined with quasi-harmonic Debye approximation (QHA). The calculated results illustrate η′ possess high formation enthalpy with lower structural stability at high temperature, which may transits to equilibrium phase η at temperature range of 510–520 K. The calculated thermodynamic properties indicate η exhibits better thermal stability than η′ at high temperature. The thermoelastic properties of η′ and η were estimated based on the temperature-dependent elastic constants Cij(T), and it is revealed the elastic moduli of η′ are larger than that of η though both two phases become deformable with elevated temperature. Moreover, the evaluated thermoelastic anisotropies suggest η′ and η are essentially elastic isotropic on {0001} plane, while η′ exhibit serious mechanical anisotropy and angular bonding characters on both {10-10} and {01–10} planes at high temperature.

Artificial ageing of Al-7075 alloy was performed in a muffle furnace at different temperatures ranging from 120∘C to 190∘C for 3 h. The formation of MgZn2 precipitates in the aged alloy was confirmed through the XRD data. The lattice parameter and crystallite size of aluminum were increased with the increase of the ageing temperature. The scanning electron microscopy results validated the precipitates of different shapes and sizes in the aged samples. The number density of the precipitates was found to be maximum at 170∘C. The Vickers hardness of Al-7075 alloy was increased from 125 HV to 172 HV with an increase of the ageing temperature from 120∘C to 170∘C and then decreased at 190∘C. The electrochemical tests of the un-aged and aged samples (in 3.5 wt.% NaCl solution) showed a decrease in the corrosion rate (0.003 mm/y) and an increase in the corrosion potential (− 137 mV) of the alloy upon ageing up to 150∘C, indicating improvement in its corrosion resistance. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To study the forming rule, microstructures and mechanical properties of Al–Zn–Mg alloy samples produced by wire + arc additive manufacturing (WAAM), a metal inert gas (MIG) arc was used as the heat source and 1.2-mm-diameter Al–6.2Zn–2.2Mg welding wires were used as the raw materials during single-pass, single-layer deposition and single-pass, multilayer deposition. In the single-pass, single-layer deposition, as the heat input increased, the number of ripples on the weld bead decreased, thereby making the surface smoother. Furthermore, under different parameters, there were always pores in the cross-section of the weld beads. In the as-deposited material, the elements were unevenly distributed due to the layer-by-layer deposition. There were two types of pores in the as-deposited material: pores caused by the presence of hydrogen and those caused by the burning loss of zinc. The as-deposited material exhibited an average hardness of 112 HV. The horizontal test samples exhibited an average tensile strength of 324 MPa, a yield strength of 208 MPa, and an elongation of 9.66%. The vertical test samples exhibited an average tensile strength, yield strength and elongation of 299 MPa, 188 MPa and 8.98%, respectively. Moreover, the samples exhibited mixed ductile–brittle fractures.

The aging stability and influence of Sn addition on precipitation kinetic were fully investigated for a novel Al–Zn–Mg aluminum alloy used for auto body structures. Microstructure evolution was characterized using Differential Scanning Calorimetry (DSC) analysis, Transmission Electron Microscopy (TEM and HRTEM), and Selected Area Electron Diffraction (SAED) techniques. Micro-hardness under different evolution was studied accordingly. Our results indicated that, the bake hardening ability was strongly improved by forming GPⅡ zone under the pre-aging treatment at 120 °C + 20 min，which is completely coherent with the matrix and has strong thermal stability. It was particularly found that the coupling of pre-aging process and Sn addition reduce the precipitation activation energy of the η′ phase from 95.38 kJ/mol in the natural aging state to 38.2 kJ/mol in the Sn-containing pre-aging state, which obviously enhances the bake hardening response.

An investigation was conducted to study the effect of soft (220 Hv) and hard (750 Hv) steel projectiles on an Al-Zn-Mg-Cu alloy processed by hot extrusion followed by heat treatment (solid solution treatment at 743 K/1.5 h + ageing treatment at 388 K/24 h). The results show that the hardness of the projectile material can influence on the shape and size of the perforation channel formed after the penetration. The hard steel projectile has longer depth of penetration and the crater front diameter is narrower comparing with the Al alloy after penetration by the soft steel projectile. Adiabatic shear bands (ASBs) are formed in the perforation channel after penetration with presence of recrystallized grains within these bands. The ASBs are wider after the hard steel projectile penetration with presence of cracks comparing with the ASBs formed after the soft steel projectile penetration. Precipitates are increased in size and overlapped in the perforation channel which are mainly of G.P. zone and η' precipitates. Hardness values of the Al alloy after penetration increase in the upper side of the perforation channel over the middle and end regions of the channel.

Al-7.02Zn-2.6Mg-0.35Mn alloy prepared by vacuum melting is selected as the research material. Effect of the homogenization, solution treatment and two-stage aging on hardness, microstructure and corrosion resistance are studied. The results show that two hardness peaks are founded in the age hardening curve of Al-7.02Zn-2.6Mg-0.35Mn alloy under the final aging processing of 160 ℃×8 h. The first hardness peak (peak I) of 176.80 HB is observed at 4 h pre-aging, and the second hardness peak (peak Ⅱ) of 173.90 HB is observed at 8 h pre-aging. The main phase of Al-7.02Zn-2.6Mg-0.35Mn alloy is included α(Al) and MgZn2. As the two-stage aging processing is 105 ℃×8 h + 160 ℃×8 h, fine transition phase (MgZn2′) is distributed uniformly on the matrix, and the coarse and discontinuous MgZn2 phase is observed at the grain boundary. As the pre-aging time increases from 4 h to 8 h, the polarization curves shift to the left obviously. The self-corrosion potential drops from -872.81 V to -865.43 V, and the corrosion current density drops from 50.12 μA/cm² to 39.35 μA/cm². The capacitive arc resistance of the peak Ⅱ alloy is twice that of the peak I alloy. Peak Ⅱ alloy has higher corrosion resistance than peak Ⅰ. From the analysis of electrochemical impedance and corrosion morphology, it can be concluded that the electrochemical corrosion of Al-7.02Zn-2.6Mg-0.35Mn alloy in 3.5% NaCl solution is the pitting induction period. [ABSTRACT FROM AUTHOR]

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To explore the correlation between the stress corrosion sensitivity and formation processing for high-strength Al-Zn-Mg alloy, extrusion surface and the matrix were investigated by microstructural characterizations, electrochemistry, and stress corrosion cracking (SCC) tests. Larger, but with low density and discontinuity, grain boundary precipitates (GBPs, − 60 nm and − 3.7% area fraction) and intermetallic particles (IMPs, − 0.5% area fraction) were achieved in the secondary recrystallized (SR) coarse-grained layer compared with the non-recrystallized matrix. The maximum Volta potential differences between the IMPs and Al matrix were about 373 mV, causing the pitting initiation by micro-galvanic effect. The decreased pitting density and the low residual stress in the SR layer reduced the available initiation sites for SCC. Thus, the SR layer acted as a barrier layer to reduce the SCC susceptibility of the extruded Al-Zn-Mg alloy in Cl−-containing environments. [ABSTRACT FROM AUTHOR]

The evolution of grain boundary (GB) of an Al–Zn–Mg alloy profile with heterogeneous structures is studied based on in-situ EBSD tensile. This evolution is not only related to its grain boundary misorientation angle (GBMA) and slip transfer parameter (m'/(Δb/b)) but also to the behavior of the geometrically necessary dislocation (GND) tensor in the deformation. The effect of GBMA and m'/(Δb/b) for three types of high angle grain boundary (HAGB) on GND density and back stress has been revealed. The increase of GND density is not obvious near the HAGBs with 45°–55° GBMA of neighboring coarse grains or neighboring fibrous grains. The optimal grain boundary for forming back stress is the HAGBs between coarse grain and fibrous grain, which has 35°–45° GBMA and a low m'/(Δb/b). The back stress is hard to form near these HAGBs with 25°–35° GBMA and a low m'/(Δb/b). Combined with the neighboring grain type, slip transfer and GBMA, the new criterion is proposed to predict GND behavior near HAGBs. [ABSTRACT FROM AUTHOR]

Controlling the balance between mechanical properties and stress corrosion resistance of Al–Zn‒Mg alloys by aging tempers has long been an active focal point of research. Traditional peak-age can improve the mechanical properties, but the continuous precipitate at the grain boundary reduces the stress corrosion resistance of the alloy. While alloys in over-aged (T73) condition show good resistance to stress corrosion, their mechanical properties will drop significantly. In this paper, tensile properties, resistances to stress corrosion, and microstructures of the Al–Zn‒Mg alloy, in interrupted aged (T5I4, T5I6) and traditional (T5, T73) tempers, were studied using a tensile test, a slow strain rate tensile test, and transmission electron microscopy. Results reveal that the tensile strength of T5I4 temper is 400.0 MPa, higher than that of T5,T73 tempers, while the stress corrosion resistance is clearly compromised, with index of slow strain rate testing, ISSRT, of 5.7%, significantly larger than that of the other three aging treatments. The tensile strength of the T5I6 temper increases to 408.5 MPa, and the stress corrosion resistance is also improved, to ISSRT=3.2%, significantly lower than that of T5 and T5I4 tempers. Volume fraction (8.8%) and average particle diameter (2.0 nm) of intragranular precipitates of T5I4 temper has the minimum value among the four aging treatments, and there are large numbers of fine precipitates distributed continuously at grain boundaries. In the T5I6 temper, the number of intragranular precipitates increase significantly, and the volume fraction of intragranular precipitates is 24.6%, larger than that of the other three aging treatments. In addition, the average particle diameter (4.1 nm) of the intragranular precipitates of the T5I6 temper is larger than that of the T5I4 temper, but is still smaller than that of the T5 and T73 tempers. Precipitates at the grain boundaries of the T5I6 temper are unevenly distributed, and significantly larger than those of the T5I4 temper.

Thick-section Al-Zn-Mg aluminum alloy extrusions are key materials for manufacturing rail transit vehicles, and stress corrosion cracking (SCC) is an important engineering application problem during the service life of these materials. The effect of sampling direction on the stress corrosion cracking behavior of Al-Zn-Mg alloys was investigated through constant load tensile stress corrosion and electrochemical tests. The microstructures of specimens were analyzed in different sampling directions both before and after stress corrosion via optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Specimens with their tensile axes parallel or perpendicular to the extrusion direction of the extruded profiles were labeled as longitudinal specimens and transverse specimens, respectively. The specimens were completely immersed in a corrosive solution, a mixture of 35 g Na Cl and 1 L deionized water, with a constant unidirectional loading of 225 MPa for 360 h at 50 ± 2 ℃. The experimental results show that the transverse specimen is fractured at 315 h, whereas the longitudinal specimen does not break during the entire loading process. Thus, the transverse specimens have poor resistance to stress corrosion cracking. The corrosion current density of the longitudinal section (L-S) is0. 980 m A·cm-2, which is approximately 5 times that of the transverse section (T-S). Thus, corrosion tends to propagate along the longitudinal direction. The L-S is more susceptible to corrosion than the T-S owing to the larger misorientation difference and higher energy of the grain boundary. During the stress corrosion loading process, anodic dissolution occurs and forms corrosion pits. Then, the cooperation of the wedge force produced by the accumulation of corrosion products and constant load causes the crack to propagate along the grain boundary. Intergranular corrosion of the two types of samples is obvious under all immersion corrosion conditions. Different specimens exhibit the tendency to undergo stress corrosion cracking.

Selective laser melting (SLM) offers obvious advantages in the production of complex parts. However, the traditional 7xxx series aluminum alloy has a serious cracking tendency in the SLM process. Therefore, in order to analyze the microstructure and cracking mechanism, and obtain crack-free aluminum alloy fabricated by SLM, this paper studied the microstructure characteristics of as-deposited Al-6.2Zn-2Mg-xSc-xZr alloy with different Sc, Zr content, as well as the influence mechanism of Sc, Zr on cracking. The results show that with the increase of Sc and Zr content, the crack tendency and grain size decrease. When Sc and Zr content reach 0.6% and 0.36% respectively, cracks can no longer be observed in the as deposited alloy. The microstructure of the as deposited Al-6.2Zn-2Mg-0.6Sc-0.36Zr alloy consists of fine equiaxed and columnar crystals, in which Sc and Zr mainly exist in the aluminum matrix as solid solutions, and some exist in the form of Al3(Sc, Zr). The immediate reason for the absence of cracks is that the microstructure changes from coarse columnar grains to fine equiaxed-columnar grains when the content of Sc and Zr increases. The refined grain size may have the following beneficial effects: It helps with reducing the thickness of the liquid films. This will increase the tear sensitivity of the liquid film and the cracking tendency and therefore lowers the hot cracking tendency; And a refined grain size improves fracture roughness, leading to an enhanced cracking resistance. At the same time, the refinement of the grains will make the feeding channel of the grain boundary shorter and easy to feed, and the fine equiaxed grains can coordinate stress-strain during solidification more effectively than coarse columnar grains, which will decrease the cracking tendency.

In this study, optimization of equal channel angular pressing (ECAP) parameters was aimed to improve the mechanical and microstructure properties of Al–Zn–Mg alloy using the Taguchi method with ANOVA analysis. Three different parameters (process temperature, processing route, and the number of passes) with three different levels were examined so L9 (33) orthogonal array was employed. The effects of these parameters on the microstructure properties of Al–Zn–Mg alloy were studied using X-ray diffractometer, optical microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy and mechanical properties were measured by Vickers micro-hardness experimental tests. Among the samples obtained, the sample that meets the desired hardness and grain size value was characterized. The results indicate that eight pass ECAP in route Bc at 100 °C is found as a more appropriate condition that meets the highest micro-hardness value and the lowest grain size value. Microstructural investigations showed that grain size was highly affected by the temperature, and is less affected by the number of passes and ECAP routes. The results showed that the increasing ECAP temperature leads to a decrease in the fraction of HABs, an increase in the grain size and an increase in the equiaxed of the grains. [ABSTRACT FROM AUTHOR]