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Microporosity formed in the solidification process of Al alloys is detrimental to the alloy properties. A two-dimensional cellular automaton (CA) model was developed to simulate the microstructure and microporosity formation in Al-Cu alloys, considering variations in Cu content and solidification rate. The results indicate that the Cu content primarily influences the growth of microporosity. To validate the model, directional solidification experiments were conducted on Al-Cu alloys with varing Cu contents and withdrawal rates. The experimental results of dendrites and microporosity characteristics agree well with the predictions from the developed model, thus confirming the validity of the model. The alloy's liquidus temperature, dendrite morphology, and hydrogen saturation solubility arising from different Cu contents have significant effects on microporosity morphology. The withdrawal rate primarily affects the nucleation of hydrogen microporosity by altering cooling rates and dendritic growth rates, resulting in different microporosity characteristics. [ABSTRACT FROM AUTHOR]

The subject of the presented research is the influence of molybdenum on selected properties of alloys that are based on the Al-Cu system. It could be observed that the introduction of molybdenum to the multi-component alloy at levels of up to 0.5 wt.% showed increases in the degrees of undercooling ΔT along with the increasing contents of the introduced element. The addition of molybdenum contributed to the reduction of the size of the primary grains of the α(Al) phase. Molybdenum improved the strength of the alloy while achieving elongation at a significant level. This is an element that occurs in the alloy – both in the iron-manganese phases and in the segregates inside the grains. Most of the iron-manganese phases occurred in a more spheroidal form. Additionally, tests were carried out on higher molybdenum content in the alloy. The addition of the tested chemical element at a level of 1 wt.% caused the precipitation of the phases that contained molybdenum, which did not dissolve after heat treatment.

This research aims to evaluate horizontal and vertical constrained rod casting (CRC) molds on hot tearing susceptibility (HTS) of Al-xCu casting alloys with 2.2, 3.6, 7.5, and 12.5 percent Cu. The hot tears on the casting product were observed using a macroscopic approach. In addition, the hot tearing susceptibility of each casting product prepared using these molds was evaluated using the HTS formula. The results show that the vertical CRC mold has a higher HTS value than the horizontal CRC mold. The rod length is a significant factor in causing hot tearing. Longer rods are more susceptible to hot tearing. The horizontal CRC mold provides a clearer effect of rod length and Cu composition on the average HTS value. In the vertical CRC mold, the effect of Cu composition on the average HTS value is less clear. Therefore, it is highly recommended to use horizontal CRC mold for HTS testing of aluminum casting alloys. [ABSTRACT FROM AUTHOR]

This study presents an innovative liquid-nitrogen cooling (LNC) strategy to address hydrogen porosity in Wire and Arc Additive Manufactured (WAAM) Al-Cu alloys, which negatively affects part properties. A coupled thermo-mechanical finite element model, calibrated with in-situ measurements, is used to analyse the thermal, mechanical and metallurgical evolutions of two single-walls fabricated with conventional gas cooling (CGC) and LNC, respectively. A hydrogen solute coupling model evaluates hydrogen supersaturation during solidification. The LNC strategy significantly reduces porosity by optimising the solidification process: (i) Grain size is reduced, lowering hydrogen concentration at the solid/liquid interface; (ii) The length and duration of the hydrogen supersaturation region are shortened due to higher temperature gradients; (iii) Enhanced Marangoni convection and reduced molten pool depth facilitate hydrogen bubble escape. Compared to the CGC part, the LNC part shows a 63.8% reduction in pore density and a 59.4% reduction in overall porosity, achieving a final porosity of 0.39%. This improves mechanical properties, with the LNC component displaying a yield strength of 100.3 MPa, ultimate tensile strength of 250.1 MPa and elongation to failure of 19.4%. Despite a slight increase in residual stresses, the LNC strategy prevents cracking in Al-Cu alloys with high cracking susceptibility.

Gradient grain structure materials with superior mechanical properties of high strength and high toughness have attracted widespread attention. Gradient materials can effectively improve toughness by constructing a microstructure from fine to coarse crystals inside the material, which has gradually become a hotspot of attention in the academic and engineering communities. In this paper, based on the crystal plasticity intrinsic theory, dislocation density is introduced as a characterization quantity, and cohesive units are added at grain boundaries to simulate damage fractures. The results of this study reveal the fracture damage mechanism of gradient crystal structure materials, providing new ideas and methods for the design of gradient materials. [ABSTRACT FROM AUTHOR]

The trade‐off relation between strength and plasticity is the bottleneck that limits the development of high‐strength and high‐plasticity Al–Cu alloys. Inspired from the influence of precipitate shape on the work‐hardening behavior of Al–Cu alloys, an Al–Cu–Zr–Sc alloy containing a mixed microstructure of spherical‐shaped Al3(Zr, Sc) phases and disk‐shaped θ′ phases is successfully designed and fabricated. Surprisingly, it is found that the strength and plasticity of the Al–Cu–Zr–Sc alloy are synchronously improved compared to the Al–Cu alloy with only disk‐shaped θ′ phases. The introduction of spherical‐shaped Al3(Zr, Sc) phases can increase the yield strength without sacrificing the work‐hardening ability of the Al–Cu–Zr–Sc alloy, which is mainly attributed to the extremely small strain‐hardening exponent of the Al alloy with spherical‐shaped precipitates. Besides, the predicted strength–elongation relation of the Al–Cu alloy is established based on the exponential strain‐hardening model. [ABSTRACT FROM AUTHOR]

Aging treatments have been widely utilized for enhancing the mechanical properties of many materials, such as Al–Cu alloys. In conventional aging treatments, there is a trade-off between the aging conditions (e.g., aging times and temperatures) and the mechanical properties (e.g., hardness and strength). There is usually compensation in the aging treatments, such as deteriorated hardness of the alloys, when tuning the aging conditions. The ultrasound-promoted aging treatments were conducted in this study to solve the aforementioned conventional difficulties since it is believed that the ultrasound could accelerate the diffusion of the atoms and thus shorten the aging time while keeping the aging temperature low. The Al-4 wt.% Cu alloys were utilized for the verification of the influence of the ultrasound on the mechanical properties of the alloys since the Al-4 wt.% Cu alloys have been widely studied. It was found that with the promotion of the ultrasound, the micro Vickers hardness of the alloys could be enhanced. On the other hand, the alternations of strength and elongation by applying an ultrasound were limited. It is therefore concluded that the ultrasound could have certain positive effects on the enhancement of the alloy properties, such as micro Vickers hardness.

Hard and brittle Fe-rich phases are formed during the solidification of recycled Al–Cu alloys, significantly decrease the mechanical properties of the alloy. In this study, optical microscopy (OM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), X-ray diffraction (XRD), synchrotron X-ray imaging and thermodynamic calculations were used to investigate the microstructure evolution influenced by ultrasonic melt processing (USMP) and cooling rate during solidification. The results show that increasing the cooling rate after USMP significantly refines the α-Al grain size and inhibited the growth of Fe-rich phase, Al2Cu and pores. The three-dimensional (3D) morphologies of the Fe-rich phase and Al2Cu changed from coarse dispersion to fine compact, their local thickness and mean radius decrease. The observed effects are attributed to the fact that both USMP and increased cooling rate reduce α-Al grain size, leading to the growth of the eutectic Fe-rich phase and Al2Cu within the confined spaces between the α-Al dendrites during the late solidification stage. The cooling rate of 1.2Fe alloy increases from 0.1 °C/s to 1.5 °C/s, there is a rise in the number of Fe-rich phases, accompanied by a decrease in their dimensions. Meanwhile, the increased cooling rate inhibits the diffusion of Fe elements, which in turn promotes the growth of the Fe-rich phase. Also, an increased increasing the cooling rate after USMP can inhibit the growth of pores, especially in 0.7FeU alloy, where the pores basically disappear.

As more industries move to capitalize on the technological benefits of additive manufacturing, researchers are exploring ways to design new alloys with properties that cannot be achieved through traditional manufacturing methods. One approach is to tailor the solidification microstructures of lightweight components using dense materials. This study examines the microstructures and mechanical properties of near eutectic Al-Cu alloys under different thermal histories, covering both high and low solidification rates found in various additive manufacturing techniques. Slow cooled lattice structures of diamond type unit cell were produced at a relatively low cooling rate by a hybrid investment casting process involving 3D printing of the lattice patterns, and rapid solidified powders of various sizes were generated by Impulse Atomization. Microstructural analysis revealed different eutectic morphologies and spacing depending on the cooling rate and location. The alloys strength was increased by spheroidization of their eutectic phases. The alloys eutectic structures were spheroidized using two spheroidization mechanisms, including (i) Thermo-mechanically by plastic deformation of as solidified samples, followed by heat treatment, and (ii) Chemically by addition of Mg and Si to the near eutectic Al-Cu alloy. Both the thermo-mechanical and the chemical spheroidization mechanism are found to improve the mechanical properties of the alloys. This study demonstrates a potential cost-effective use of heavy alloys in high-performance applications through additive manufacturing (e.g. using lattice structures) by optimizing microstructures and enhancing mechanical properties.

To investigate the effect of the microstructure adjacent to the grain boundaries on the mechanical properties and hydrogen embrittlement susceptibilities in the Al-Cu base 2219 alloy, alloy specimens were solution-treated and then aged at 100°C, 130°C, and the usual aging temperature of 190°C, to control the alloy microstructure in the vicinity of grain boundaries. The slow strain rate technique was conducted on the specimens in humid air and dry nitrogen gas environments to evaluate the effect of environmental hydrogen on them. Transmission electron microscopy was used to measure the grain boundary precipitate size and precipitate-free zone width of the specimens. Thermal desorption analysis was conducted on the gauge sections of the fractured specimens to evaluate the trapping sites and amount of hydrogen desorbed. The specimens aged below 190°C had finer grain boundary precipitates than those aged at 190°C. The test environment did not affect the specimen strength under any of the aging conditions 100°C, 130°C, and 190°C. Some samples had intergranular fractures on their entire fracture surfaces, irrespective of the test environment. The thermal desorption analysis results showed no significant difference between the hydrogen emission spectrum and the amount of hydrogen released within each temperature range. Thus, hydrogen embrittlement does not occur in the 2219 alloy, irrespective of the characteristics of its microstructure adjacent to the grain boundaries. [ABSTRACT FROM AUTHOR]

Gradient grain structure materials with superior mechanical properties of high strength and high toughness have attracted widespread attention. Gradient materials can effectively improve toughness by constructing a microstructure from fine to coarse crystals inside the material, which has gradually become a hotspot of attention in the academic and engineering communities. In this paper, based on the crystal plasticity intrinsic theory, dislocation density is introduced as a characterization quantity, and cohesive units are added at grain boundaries to simulate damage fractures. The results of this study reveal the fracture damage mechanism of gradient crystal structure materials, providing new ideas and methods for the design of gradient materials.

Powder metallurgy stands out as a preferred manufacturing method across various industries due to its advantages in design flexibility, material efficiency, and cost-effective production. In this work, we study the influence of different compaction directions on the strength characteristics of parts produced using powder metallurgy. Al–4 wt.%Cu alloys are used due to their recyclability. We use three distinctive compaction pressures. After sintering, samples are either air-cooled or water-quenched and naturally aged (T4 temper). Both the compressive and tensile strengths are characterized and thoroughly analyzed. This research highlights the significant impact of both heat treatments and compaction directions on anisotropic strengths. The novelty of this research lies in the use of powders that can be reclaimed from machining, turning, or foundry rejections. By eliminating or minimizing the melting stage and employing powder metallurgy, we achieve cost-effective and environmentally friendly processes. Furthermore, we underscore the critical role played by careful planning of compaction loads, compaction directions, and heat treatments in determining the final mechanical performance. This approach is not only economically viable but also aligns with the growing adoption of environmental, social, and governance (ESG) practices in industry. [ABSTRACT FROM AUTHOR]

Externally physical fields such as stress field, electric field and magnetic field have been demonstrated influence the equilibria and kinetics of solid-state transformations in metals and alloys. This review focuses on the effects of externally physical fields on the aging precipitation of aerospace Al alloys including 2xxx Al-Cu alloys, 7xxx Al-Zn-Mg alloys as well as the advanced Al-Li alloys. While the η' phase in Al-Zn-Mg alloy and the T1 phase in Al-Li alloy showed no obvious stress-orientating effect, the precipitation of θ' phase in Al-Cu alloy showed obvious stress-orientating effect depending on the applied stress direction. Regarding precipitation kinetics, aging under stress field, electric field and magnetic field all can enhance the aging precipitation of aerospace Al alloys. The understanding of the effects of externally physical field on the aging precipitation in Al alloys is very preliminary. It appears that while the stress field acts on the thermally activated transformation, the athermal effect associating with electromigration of electromagnetic field has been considered responsible for the enhanced aging precipitat ion. [ABSTRACT FROM AUTHOR]

This investigation focuses on the effects of the compaction directions (i.e., transversal and longitudinal) and microstructural arrays (inside the powder utilized to constitute the specimens) on the anisotropic strengths. The initial powders are obtained from the as-cast Al-4 wt.% Cu alloys solidified in two distinct cooling rates, i.e., ~0.5 and 2.5 °C/s. The powder particles are compacted by using 300, 400 and 600 MPa and sintered at 540 °C for 1 h. The compressive and tensile strengths are carried out and the anisotropic strengths are determined. It is found that transverse samples exhibit higher UCS (ultimate compressive strength) and UTS (ultimate tensile strength) than the longitudinal samples. It is also found that the powder compacted in the transversal direction and utilizing powder with finer dendritic arm spacing provides better UCS and UTS results. The novelty in the study concerns the fact that is evidenced in the role of the dendrite spacings concatenated with the compaction pressure and direction upon the mechanical behavior. It is concluded that depending on the compaction level intended or demanded mechanical behavior, the planning in the compaction direction is preprogrammed. Since recycled powder particles from conventional machining, drilling and turning can potentially be utilized to constitute parts and components, the environmentally friendly aspects are associated, and hazardous stages in a manufacturing process are substantially reduced or eliminated. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate the influence of magnesium (Mg) on the mechanical properties and corrosion behavior of wrought Al–4Cu–xMg–0.6Ag alloys. The results from Optical Microscope, SEM, XRD analysis, and Thermo-Calc simulation were used to identify the microstructure formed after the aging process. Testing for hardness and tensile strength was conducted, in addition to corrosion testing. It was found that Mg significantly impacts the hardness of the alloys, with a high Mg content (low Cu/Mg ratio) increasing the hardness but reducing the tensile strength and ductility. This study attributed this to the formation of the S phase, which is dependent on both the quantity in the bulk and the size of the phase. The grain size was found to be finer with a higher Mg content, since the particle size inhibits grain growth during the artificial aging process. Counterintuitively, the corrosion activity was reduced in the high-Mg-content alloy due to its large particle size and the reduced galvanic cell effect. This study highlighted the importance of considering the effects of Mg on the mechanical properties and corrosion behavior of Al–Cu–Mg–Ag alloys. [ABSTRACT FROM AUTHOR]

Bu çalışmada, toz metalürjisi tekniğinin en önemli aşamalarından biri olan ham pelet üretiminde uygulanan sıkıştırma basıncının, üretilen malzemenin mikro yapı ve mekanik özellikleri üzerindeki etkileri incelenmiştir. Bu bağlamda, %99 saflığa sahip ortalama 44 µm boyutlarındaki Al ve Cu tozları kullanılarak, hafif olmasının yanı sıra dayanım bakımından etkili olan Al-15Cu alaşımı üretilmiştir. Mekanik olarak karıştırılan alaşım tozları, özel olarak tasarlanmış kalıp içerisine yerleştirilerek tek eksenli kuvvet uygulaması ile 350, 470 ve 600 MPa basınç altında ayrı ayrı sıkıştırılmıştır. Sıkıştırma işlemi sonrasında ham pelet haline gelen üç farklı numune, tavlama fırınında 550 oC sıcaklıkta 45 dakika bekletilerek geleneksel sinterleme işlemine tabi tutulmuştur. Üretimi tamamlanan numunelerin mikro yapı, yoğunluk, mikro sertlik ve basma dayanımı özellikleri belirlenerek kendi aralarında kıyaslanmaları sağlanmıştır. Yapılan değerlendirmeler sonucunda, sıkıştırma basıncının artırılması ile numunelerin gözenek oranlarının azaldığı ve buna bağlı olarak deneysel yoğunluklarının arttığı tespit edilmiştir. Buna ek olarak artan basınç oranının numunelerin mikro yapı özellikleri üzerinde değişime neden olduğu ve bu değişimin mikro sertlik (80→148 HV) ve basma dayanım değerlerinde (221→508 MPa) iyileşmeye neden olduğu belirlenmiştir. Elde edilen sonuçlar neticesinde uygun basınç oranı ile ham pelet haline dönüştürülen numunelerin, geleneksel olarak sinterlenmesi günümüz teknolojisinde kullanıma uygun malzemelerin üretiminin gerçekleşebileceği ortaya konulmuştur.

θ' -Al 2 Cu precipitates in Al-Cu alloys have various distorted octagon shapes, which can be explained by the competition between {100} and {110} type semi-coherent interfaces with the Al matrix. While most prior studies on the semi-coherent Al/ θ' interfaces have focused on the {100} orientation, little is known about the {110} interface. We have investigated the energetics of pristine and solute-segregated {110} semi-coherent Al/ θ' interfaces with advanced characterization and first-principles studies. We report interfacial, strain, and solute segregation energetics of the {110} Al/ θ' semi-coherent interface for 39 elements and compared them with previously reported values of the {100} interface. We discuss the atomic features and atomic local structures to identify similarities and differences between the two types of Al/ θ' semi-coherent interfaces. The isotropy in pristine Al/ θ' semi-coherent interfacial energy and the anisotropy resulting from solute segregation provide insight into the formation of different types of θ' precipitate "faces" reported in the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

The present work was performed on three versions of a newly developed alloy coded T200 containing 6.5% Cu, 0.1% Fe, 0.45% Mg, and 0.18% Zr in addition to A319 and A356 alloys (grain refined and Sr-modified). Tensile bars were subjected to 13 different heat treatments prior to testing at either 25 °C or 250 °C. The tensile data were analyzed using the quality index method. The results obtained showed that, due to the high copper content in the T200 alloy coupled with proper grain refining, the alloy possesses the highest quality as well as improved resistance to softening when tested at 250 °C among the five alloys. The results also demonstrate the best heat treatment condition to maximize the use of the T200 alloy for automotive applications. Grain-refined alloy B, treated in the T6 temper and tested at 250 °C, exhibited the best combination of the four tensile parameters, i.e., UTS, YS, %El, and Q-values: 308 MPa, 304 MPa, 2.3%, and 352 MPa, respectively, which are comparable with those obtained from the 356 alloy: 309 MPa, 305 MPa, 2.8%, and 375 MPa in the same order. [ABSTRACT FROM AUTHOR]

Powder metallurgy stands out as a preferred manufacturing method across various industries due to its advantages in design flexibility, material efficiency, and cost-effective production. In this work, we study the influence of different compaction directions on the strength characteristics of parts produced using powder metallurgy. Al–4 wt.%Cu alloys are used due to their recyclability. We use three distinctive compaction pressures. After sintering, samples are either air-cooled or water-quenched and naturally aged (T4 temper). Both the compressive and tensile strengths are characterized and thoroughly analyzed. This research highlights the significant impact of both heat treatments and compaction directions on anisotropic strengths. The novelty of this research lies in the use of powders that can be reclaimed from machining, turning, or foundry rejections. By eliminating or minimizing the melting stage and employing powder metallurgy, we achieve cost-effective and environmentally friendly processes. Furthermore, we underscore the critical role played by careful planning of compaction loads, compaction directions, and heat treatments in determining the final mechanical performance. This approach is not only economically viable but also aligns with the growing adoption of environmental, social, and governance (ESG) practices in industry.

This investigation focuses on the effects of the compaction directions (i.e., transversal and longitudinal) and microstructural arrays (inside the powder utilized to constitute the specimens) on the anisotropic strengths. The initial powders are obtained from the as-cast Al-4 wt.% Cu alloys solidified in two distinct cooling rates, i.e., ~0.5 and 2.5 °C/s. The powder particles are compacted by using 300, 400 and 600 MPa and sintered at 540 °C for 1 h. The compressive and tensile strengths are carried out and the anisotropic strengths are determined. It is found that transverse samples exhibit higher UCS (ultimate compressive strength) and UTS (ultimate tensile strength) than the longitudinal samples. It is also found that the powder compacted in the transversal direction and utilizing powder with finer dendritic arm spacing provides better UCS and UTS results. The novelty in the study concerns the fact that is evidenced in the role of the dendrite spacings concatenated with the compaction pressure and direction upon the mechanical behavior. It is concluded that depending on the compaction level intended or demanded mechanical behavior, the planning in the compaction direction is preprogrammed. Since recycled powder particles from conventional machining, drilling and turning can potentially be utilized to constitute parts and components, the environmentally friendly aspects are associated, and hazardous stages in a manufacturing process are substantially reduced or eliminated.

The present study aimed to investigate the influence of magnesium (Mg) on the mechanical properties and corrosion behavior of wrought Al–4Cu–xMg–0.6Ag alloys. The results from Optical Microscope, SEM, XRD analysis, and Thermo-Calc simulation were used to identify the microstructure formed after the aging process. Testing for hardness and tensile strength was conducted, in addition to corrosion testing. It was found that Mg significantly impacts the hardness of the alloys, with a high Mg content (low Cu/Mg ratio) increasing the hardness but reducing the tensile strength and ductility. This study attributed this to the formation of the S phase, which is dependent on both the quantity in the bulk and the size of the phase. The grain size was found to be finer with a higher Mg content, since the particle size inhibits grain growth during the artificial aging process. Counterintuitively, the corrosion activity was reduced in the high-Mg-content alloy due to its large particle size and the reduced galvanic cell effect. This study highlighted the importance of considering the effects of Mg on the mechanical properties and corrosion behavior of Al–Cu–Mg–Ag alloys.

Additive manufacturing (AM) technologies have been used to repair aluminum (Al) alloy components in many engineering structures. However, the use of AM technologies to repair Al-Cu alloys is still very limited, and the repair via electron beam directed energy deposition (EB-DED) has not been reported so far. In this work, the EB-DED repair was performed on AlCu4MgSi-O Al alloy substrate with the specially developed Al-Cu-Si wire (380D). The results show that wall structures with high metallurgical quality were successfully prepared. The deposit exhibits alternating fine grain zones and coarse grain zones. In the bottom layers of deposit, columnar grains growing along building direction dominate, while the middle and top layers mainly consist of equiaxed grains. In the AlCu4MgSi-O substrate, the heat-affected zone (HAZ) close to the fusion line undergoes recrystallization and completely transforms into fine equiaxed grains, while abnormal grain growth occurs and coarse grains are formed in the HAZ slightly away from the fusion line. From substrate to deposit, the intensity of texture gradually decreases. After EB-DED repair, the microhardnesses and strengths of the bottom layers and HAZ are significantly improved. The strengthening of HAZ is entirely attributed to precipitation strengthening, while the bottom layers are affected by both precipitation strengthening and dispersion strengthening. Tensile tests indicate that the repaired structure samples fracture from the interface between HAZ and base metal zone of the AlCu4MgSi-O substrate. EB-DED is demonstrated to be a promising technology to repair AlCu4MgSi alloy components, and this work can serve as a useful reference for the high-quality repair of Al-Cu alloy structural parts. • EB-DED was used for the first time to repair AlCu4MgSi-O alloy, with the specially developed Al-Cu-Si wire. • The evolution of grain morphology, precipitation behaviors and mechanical properties from substrate to deposit was studied. • After EB-DED process, the closer to the fusion line, the more are θ′ precipitates. • The thin-wall repaired structure exhibits higher strength than the AlCu4MgSi-O matrix. [ABSTRACT FROM AUTHOR]

Microstructural evolution and creep response were investigated in the cast Al-5.0Cu-0.3Mn-0.2Zr (wt.%) alloy with and without addition of slow-diffusing, intermetallic-forming elements Fe, Ni, or Co. Baseline Al-5.0Cu-0.3Mn-0.2Zr alloy exhibits high creep resistance at 300 °C, up to ∼75 MPa, which is attributed to high-aspect-ratio, intragranular θ′-Al 2 Cu precipitates that effectively suppress dislocation climb. However, θ′-Al 2 Cu precipitate-free zones form along grain boundaries upon heat treatment, whose extent is amplified during subsequent creep. Such weak regions experience dislocation creep, leading to strain localization and acceleration of grain-boundary sliding. Adding Ni and Co, individually or in combination, leads to the formation of grain-boundary precipitates (Al 9 Co 2 , Al 3 Ni 2) which are resistant to coarsening, thus suppressing the formation of θ′-Al 2 Cu precipitate-free zones. This microstructure provides high creep resistance at stresses up to 75–80 MPa, with strain rates much lower than in unmodified Al-5.0Cu-0.3Mn-0.2Zr. Adding Fe, which results in extensive decoration of grain boundaries with coarsening-resistant Al 7 Cu 2 Fe, and then increasing the Cu content to compensate for the Cu loss to this new phase, leads to a new Al-7.4Cu-1.6Fe-0.3Mn-0.2Zr alloy with creep resistance at 300 °C that surpasses known cast aluminum alloys. Adding Fe to improve the creep resistance of Al-Cu alloys is both cost-effective and sustainable. Our findings offer guidelines applicable to various alloy systems on controlling the evolution of precipitate-free zones and its ensuing effects on creep deformation. [ABSTRACT FROM AUTHOR]

Solute segregation at the interface between the aluminum (Al) matrix and the Ω ( Al 2 Cu) phase decreases the interfacial energy, impedes the coarsening of precipitates, and enhances the thermal stability of such precipitates. In this study, we employ density functional theory to systematically calculate solute segregation energies of 42 solute elements at the coherent and semi-coherent interfaces between the two phases, as well as mixing energies of these elements within the Al and Cu sublattices of the Ω phase. Using correlation analysis and machine learning methods, we establish the relationship between the solute segregation energy and 20 selected atomic descriptors. Metalloid and late transition metal elements are predicted as potential candidates for enhancing the thermal stability of Al–Cu alloys. We observe that the solute segregation energy at the interfacial site of the semi-coherent interface correlates with the atomic size of solute atoms and their solubilities within the Ω phase. The developed machine learning models exhibit the potential to predict solute segregation energies at various sites of the coherent and semi-coherent interfaces. Overall, our study provides valuable insights into the stabilizing potential of individual elements at the Ω /Al interface in Al–Cu alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

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Electric vehicles are a viable alternative for internal combustion engine cars to overcome transportation problems due to high fossil fuel consumption and greenhouse gas emissions. Due to their direct current motor and battery technologies' technological development, they have become an efficient transportation option in the last decades. However, the rapid spread of electric vehicles will bring huge dump problems for the environment. Thus, policies related to the recycling of their components must be carried out. In this study, an Al–Cu alloy is developed from the waste direct current motor's Cu rotor coils and pure Al for hydrolysis reactions. Then, 2 wt%, 4 wt% and 6 wt% Cu are added to pure Al to observe different Cu addition to Al–Cu alloy's hydrogen production performance to varying temperatures like 40, 60, and 80 °C. In 40 °C, 6 wt% Cu added Al alloy has around two-fold higher hydrogen production than pure Al. Moreover, the hydrolysis reaction's activation energy is decreased from 81.56 to 35.5 kJ mol−1 in 6 wt% Cu added Al alloy. [Display omitted] • Al–Cu alloy is developed from waste DC motor's Cu rotor coils and pure Al. • Activation energy is decreased from 81.56 to 35.5 kJ mol−1 in AlCu6 alloy. • In AlCu6 alloy, 0.17 ml s− 1 hydrogen generation rate is obtained at 40 °C. • Corr rate of the pure Al is changed from 28.78 to 86.56 ml g−1 min−1 by 6 wt% Cu addition. [ABSTRACT FROM AUTHOR]

The effect of post-process aging on the microstructure and mechanical properties of multi-pass friction stir processed (FSPed) Al-4.5Cu alloy containing Si (1, 3, and 5 wt.%) was studied. According to the results, adding Si improved the fluidity and decreased the porosity content of the alloy. The addition of Si up to 3 wt.% also enhanced the mechanical properties. However, further addition of Si up to 5 wt.% impaired the tensile properties. Applying the first pass of FSP improved the tensile strength and fracture strain of the alloy containing 3 wt.% Si by 25 and 125%, respectively. However, the second and fourth pass of FSP substantially improved the fracture strain, but deteriorated the hardness and tensile strength of the alloy containing 3 wt.% Si. Post-FSP aging at 180 °C for 8 h significantly improved the mechanical properties. For instance, compared to the as-cast condition, the hardness, tensile strength, fracture strain, and toughness of post-aged four-pass FSPed Al-4.5Cu-3Si alloy increased by 107, 108, 175, and 310%, respectively. According to the fractography results, the fracture surface morphology of Al-4.5Cu-3Si alloy changed from a quasi-cleavage mode in as-cast condition to a ductile-dimple fracture mode after post-FSP aging. [ABSTRACT FROM AUTHOR]

Ceramic layers were deposited on Al–xCu (x = 1, 3, and 4.5 wt-%) alloys by micro-arc oxidation (MAO) at oxidation times of 10 and 24 min. Effects of changes in electrical conductivity (EC) and thermal conductivity (TC) of the substrate on microstructure, phase composition, residual stress (RS), and thermal shock resistance (TSR) of the layers were studied. The low EC was not conducive to the formation of α-Al2O3 at the 10 min oxidation. The low TC contributed to the increasing coating thickness and residual compressive stress (RCS) formation. Coatings on the alloy with 1 wt-% Cu exhibited residual tensile stress (RTS). The cavity formation induced by Al2Cu phase affected the current and RS. The results of thermal shock tests showed that the high TC and RTS in the ceramic layers impaired the TSR. The RCS together with the high TC caused the significant cohesive failure. [ABSTRACT FROM AUTHOR]

Solidification cracking (SC) is highly related to the grain coalescence behavior during welding of aluminum alloys. In this study, the grain coalescence behavior and its effects on solidification cracking susceptibility (SCS) were investigated using the multiphase-field approach. Why SCS is high at a certain value of Cu concentration and why SC often occurs at high misorientation angles are revealed. Firstly, nominal compositions of Cu affect the morphology of microstructure during solidification. The crystals morphology is cellular at the low concentration, while the crystals are dendritic at the high concentration in the columnar grain region. The SCS of cellular grains is higher than dendrites due to the high volume fraction of solid when the grains/subgrains bridge. Under the action of tensile stress, the scarce residual liquid phase cannot backfill in time. Secondly, high misorientation angles make grain boundary energy in the solid–solid interface (σSS) is high. It is found that σSS suppresses the grain coalescence and increases the SCS of alloys. This leads the emergence of SC at high misorientation angles during welding. In this study, the coalescence behavior of grains during solidification is visually presented by simulation and the coherency point at the last-stage solidification is achieved accurately.

It has been demonstrated that the susceptibility to solidification cracking can be calculated based on the index of |dT/d(fS)1/2| (T: temperature; fS: fraction solid) near the end of solidification. To distinguish the role of transverse tension verse that of solidification shrinkage in solidification cracking, however, computational fluid dynamics was used to calculate the flow of the intergranular liquid towards the roots of columnar dendritic grains using arc welding of Al–Cu alloys as an example. The calculated results show the solidification shrinkage dominates crack formation at the strain rate of 0.0001/s, but transverse tension dominates at the strain rate of 0.1/s. In between, both solidification shrinkage and transverse tension can play a significant role. [ABSTRACT FROM AUTHOR]

Microarc oxidation (MAO) coatings were produced on the Al–Cu alloys at different oxidation times. Surface morphologies, phase composition and residual stress, and wear resistance were analysed by SEM and a laser scanning confocal microscopy, X-ray diffraction, and reciprocating friction and wear tester, respectively. Increases in surface roughness, porosity, cracks, thickness, and α-Al2O3 content were found in the MAO coatings on Al–4.5Cu alloy. Presence of intermetallic Al2Cu in the Al–4.5Cu alloy improved wear resistance and induced residual compressive stress formation in the coatings. Heat accumulation of intermetallic Al2Cu was the key factor that led to the differences in coating microstructure and nature of residual stress. In addition, mechanical properties of the coated samples were slightly changed compared to that of bare Al–Cu alloys. Presence of intermetallic Al2Cu was advantageous to wear resistance and oxide film formation of MAO coated Al–Cu alloys. [ABSTRACT FROM AUTHOR]

The present work aims to explore the effects of the alloying elements (Si, Bi, Sb, Ni, and Co) and solidification rates (V) on the microstructural morphology, microhardness, ultimate tensile strength and electrical resistivity of Al-Cu based eutectic alloys by Bridgman-type solidification apparatus, metallographic observation, scanning electron microscopy, microhardness testing, tensile testing and four-point probe testing. Firstly, the Al-33 Cu-2X (wt.%) samples were produced by using metals of high purity (> 99.95 %) in the vacuum and hotfilling furnaces; these alloys were unidirectionally solidified under different solidification rates, V (8.28-167.08 µm s-1) and constant temperature gradient, G (average 8.50 K mm-1). Secondly, metallographic examination and measurement processes: lamellar spacings (1), microhardness (HV), ultimate tensile strength (UTS) and electrical resistivity (1) were measured and expressed as functions of V. It has been found that the addition of the alloying elements (AE) content in Al-Cu eutectic as well as increasing of V lead to a decrease of lamellar spacings. On the contrary, the values of HV, UTS, and increase with increasing V values and the addition of alloying elements. Relationships between a-V, a-HV, a-UTS (s) and a-1 were found by regression analysis, and the results found in this research were compared with the previous similar studies. [ABSTRACT FROM AUTHOR]

During the solidification process, the recycled Al-Cu alloys form coarse Fe-rich phases, which seriously deteriorate the mechanical properties of the alloy. The study employed optical microscope (OM), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and synchrotron X-ray imaging to investigate the impact of cooling rate and Fe contents on the growth of Fe-rich phases, Al 2 Cu, and pores in recycled Al-Cu-Mn-Mg-Fe-Si alloys under synergistic effect ultrasonic melt processing (USMP) and Al-Ti-B. USMP can homogenize the distribution of TiB 2 particles and provides more nucleation sites for the formation of Fe-rich phases. Under the synergistic effect of USMP and Al-Ti-B, increasing the cooling rate,the volume fractions of Fe-rich phases in 0.7FeUB (0.7 wt%Fe + USMP + Al-Ti-B) and 1.2FeUB (1.2 wt%Fe + USMP + Al-Ti-B) alloys decreased from 8.92% and 16.52% to 8.03% and 14.73%, respectively. The volume fraction of Al 2 Cu increased from 4.06% and 3.13% to 4.37% and 3.54%, respectively. Furthermore, the three-dimensional (3D) morphology of Fe-rich phases and Al 2 Cu became more compact and uniform. The volume fraction of pores in the 1.2FeUB alloy decreased from 0.412% to 0.072%. In-situ synchrotron X-ray radiography revealed that increasing cooling rates led to increased nucleation undercooling of primary α-Al and Fe-rich phases. These phenomena can be attributed to the combined effects of ultrasonic cavitation, ultrasonic streaming, and an increased cooling rate. These factors serve to homogenize the alloy composition, ensure uniform distribution of TiB 2 particles, inhibit element diffusion, reduce solute segregation, and ultimately lead to the refinement of the grain size, α-Al, Fe-rich phases, and Al 2 Cu, while also inhibiting pore growth. • Increasing the cooling rate under the synergistic effect of USMP and Al-Ti-B, refine the grain size. • Under the synergistic effect of USMP and Al-Ti-B, increasing the cooling rate resulted in a more compact 3D morphology. • Increasing the cooling rate increases the nucleation undercooling and reduces the size of α-Al and Fe-rich phases. [ABSTRACT FROM AUTHOR]

Abstract—Thermodynamic calculations performed with the Thermo-Calc software and experimental methods, in particular, the high-resolution transmission electron microscopy (TEM), are used to study the effect of indium microaddition on heat-treatment-induced changes of the phase composition and character of strengthening of the Al–1.5 wt % Cu and Al–3.5 wt % Cu alloys. The 0.1 wt % indium addition is shown to completely suppress the natural aging of the Al–3.5% Cu alloy. However, indium substantially intensifies the decomposition process of the aluminum solid solution (Al) during artificial aging; this determines the advantages of microalloyed compositions over the base alloys in both the time of reaching the peak strength and hardness. In particular, after aging to the peak strength, the hardness of the Al–3.5% Cu–0.1% In alloy is ~20% higher than that of the base alloy (124 HV against 105 HV), whereas the hardness of the Al–1.5% Cu–0.1% In alloy is more than 60% higher than that of the base Al–1.5% Cu alloy (59 HV against 37 HV). TEM analysis showed that the observed increase in the hardness during aging of the microalloyed compositions is due to the formation of substantially finer structure of aging products (the average linear size of the strengthening θ' phase decreases from 100 to 50 nm) along with the higher particle distribution density. [ABSTRACT FROM AUTHOR]

An Al–Cu alloy micro-alloyed with Mn and Zr (ACMZ) was examined to understand the thermal stability and strengthening mechanism of metastable θ'-Al2Cu precipitates with interfacial segregation after prolonged thermal exposure. The microstructure was characterized at multiple scales with techniques including synchrotron x-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy, and atom probe tomography. The θ' precipitates did not exhibit measurable coarsening after thermal exposure at 300°C for 5000 h. Kinetic effects of Mn and Zr interfacial segregation, which dominate over thermodynamic effects under these conditions, were necessary to understand the complete inhibition of precipitate coarsening. The θ' phase fraction was stable during the 5000 h exposure. This stable phase fraction was regarded as the metastable equilibrium value and was smaller than that predicted by the θ' solvus line of the ACMZ alloy. As expected from the observed phase stability, the alloy hardness also remained stable during the 5000 h exposure. An Orowan mechanism alone was inadequate to explain θ' precipitate strengthening. Additional strengthening mechanisms by θ' precipitates specifically related to the transformation strain may explain the observed hardness values.

Al–Cu-based casting alloys have very high strength, but improper heat treatment will create a material susceptible to stress corrosion failure. A review of this problem is provided and discussed regarding a recent study of A205-T7 alloy castings. [ABSTRACT FROM AUTHOR]

Electrochemical studies and microstructure analysis of directionally solidified hypoeutectic and eutectic aluminum-copper alloys were performed. Optical and scanning electron microscopy studies of corroded specimens with columnar and equiaxed microstructures in 0.1 M, 0.5 M, and 1 M NaCl solutions were conducted. Low-rate potential scanning and alternating current (AC) electrode impedance measurements were conducted to study the corrosion resistance of four aluminum-copper alloys. The concentration of Cu in the alloys proved to be a key factor in the corrosion resistance of the Al-Cu alloys, which controlled the fraction of α and θ phases and the morphological distribution of these phases. The addition of Cu provides cathodic sites that increase adjacent anodic activity and higher corrosion susceptibility of the Al-Cu alloys, as compared with pure Al. Arise in the Cu amount that is linked to an increased concentration of the Al2Cu intermetallic or theta phase results in a higher susceptibility to corrosion for the studied alloys. A microstructural morphology related to a decreased area of contact between the α-phase and the Al2Cu intermetallic phase enhances the corrosion resistance of the Al-Cu alloys. For the Al-1wt.%Cu alloy increasing the content of Cl− produces a beneficial result related to a more resistive passive film. For the rest of the studied alloys with nobler corrosion potentials, the increase in Cl− results in a decrease in their corrosion resistance. [ABSTRACT FROM AUTHOR]

An effective alloying system for providing improved mechanical and technological properties of model cast Al–Cu alloys (Al-4.6%Cu-0.4%Mn-0.2%Ti), using magnetohydrodynamic (MHD) melt mixing, has been chosen in this research. It was shown that MHD treatment provides a non-dendritic (globular) ingot structure and can be applied to ensure thixotropy in the mass production of high-precision cast parts. Small additives of alloying elements that modify both grain structure (Mn, Zr) and reinforcing phases (Sn, In, Sc) were used. It is shown that the most effective alloying elements which improved the strength characteristics of the alloy are Sn and In. The introduction of 0.1–0.2% Sn or In followed by heat treatment led to a 50% increase in its yield strength, a 15% increase in the tensile strength. Sn and In modified the decomposition kinetics, providing a high density of precipitate and slow coalescence of nano-sized particles of the strengthening θ′-phase, which resulted in higher strength characteristics of the alloy. [ABSTRACT FROM AUTHOR]

The presence of complex, core–shell Al3(Zr, Sc) dispersoids in Al-Cu alloys has recently been found to significantly refine θ′ precipitates resulting in increased mechanical properties. The purpose of this work was to take advantage of these effects to develop alloys with enhanced resistance to high-temperature thermal exposure compared to industrial baseline products. A series of Sc-bearing Al-Cu alloys were designed, manufactured using tailored homogenization practices and tested. It was found that a novel Al-Cu-Mn-Zr-Sc alloy exhibited higher tensile strength than AA2219-T8511 after a thermal exposure of 280 °C—24 h. The presence of Sc-containing primary intermetallics was also observed in V-bearing compositions. [ABSTRACT FROM AUTHOR]

The influence of different types of precipitates (either Guinier-Preston zones, θ ″ or θ ′) on the critical resolved shear stress and strain hardening was determined by means of micropillar compression tests in an Al - 4 wt% Cu alloy. The size, shape and volume fraction of the precipitates were measured in each case. It was found that size effects were negligible for micropillars with diameter ≥ 5 µm. Micropillars with Guinier-Preston zones showed strain localization due to precipitate shearing. The best mechanical properties were obtained with either a fine dispersion of the θ ″ precipitates or a coarser dispersion of θ ′. Both precipitate shearing and Orowan loops were observed around the θ ″ precipitates and the micropillar strength was compatible with the predictions of the Orowan model. In the case of the alloy with θ ′ precipitates, the strengthening contribution associated with the transformation strain around the precipitates has to be included in the model to explain the experimental results. Finally, the micropillar compression tests in crystals with different orientations were used to calibrate a phenomenological crystal plasticity. This information was used to predict the mechanical properties of polycrystals by means of computational homogeneization. [ABSTRACT FROM AUTHOR]

The mechanisms of dislocation/precipitate interactions were analyzed in an Al–Cu alloy containing a homogeneous dispersion of θ ′ precipitates by means of discrete dislocation dynamics simulations. The simulations were carried out within the framework of the discrete-continuous method and the precipitates were assumed to be impenetrable by dislocations. The main parameters that determine the dislocation/precipitate interactions (elastic mismatch, stress-free transformation strains, dislocation mobility and cross-slip rate) were obtained from atomistic simulations, while the size, shape, spatial distribution and volume fraction of the precipitates were obtained from transmission electron microscopy. The predictions of the critical resolved shear stress (including the contribution of solid solution) were in agreement with the experimental results obtained by means of compression tests in micropillars of the Al–Cu alloy oriented for single slip. The simulations revealed that the most important contribution to the precipitation hardening of the alloy was provided by the stress-free transformation strains followed by the solution hardening and the Orowan mechanism due to the bow-out of the dislocations around the precipitates. Image, graphical abstract [ABSTRACT FROM AUTHOR]

It is known that processes occurring in binary system melts affect the crystallization process and the phase composition of alloys. To predict these processes, we should determine the region of thermodynamic stability of the melt. In this paper, the structural properties of hypoeutectic and hypereutectic alloys in Al–Cu system are studied depending on the heating temperature above the liquidus line and aftercooling rate. It is shown that overheating of Al–Cu melts to 150 K above the liquidus line and further cooling leads to complete suppression of the process of formation of primary aluminum crystals in hypoeutectic alloys and Al 2 Cu phase in hypereutectic alloys. For the first time, by accounting in Gibbs energy of binary Al–Cu alloy for the first degree approximation of high-temperature expansion of thermodynamic potential, the dependence of temperature of line of the melt thermodynamic stability on copper content in alloy is obtained. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of orientation and spatial distribution on CRSS is investigated. • Disk-shaped precipitates interact with the dislocation via an ellipsoidal potential field. • An orientation factor is proposed to describe the orientation related strengthening. • A modified Orowan model considering orientation distribution is suggested. • An extended model considering irregular spatial distribution of precipitates is suggested. Precipitates contribute significantly to the strength of many common engineering aluminum alloys. The stress orienting effect of disk-shaped θ′ precipitates in Al-Cu alloy may lead to varying orientation distribution of the precipitates and, thus, varying critical resolved shear stress (CRSS) and macroscopic mechanical properties. In this work, θ′ precipitates was incorporated into discrete dislocation dynamics (DDD) simulation software ParaDiS. This approach was applied to systematically investigate how CRSS is affected by the orientation distribution and spatial distribution of the θ′ precipitates which has a considerable effect on the CRSS but has received less attention in previous research. As a simplification, the orientation distribution of a one-dimensional equidistantly distributed sequence of precipitates are taken as the research object. By varying the orientation of each precipitate, DDD simulations with wide range of overall orientation distributions can be obtained. Based on this, we propose an orientation factor that can adequately define the relationship between the orientation distribution and the CRSS. A modified Orowan model considering orientation distribution with parameters calibrated by dislocation dynamics simulations is suggested in light of these investigations, enabling rapid prediction of CRSS. Subsequently, the spatial distribution of precipitates was described using the extreme distribution, and a spatial factor was created by examining the mean and variance. This model was extended to the case of complex precipitate distributions by considering the spatial factor. The accuracy of the extended model was verified through DDD simulation results for randomly distributed precipitates and the prediction accuracy was greatly improved. This work makes it possible to calculate precipitation strengthening in Al-Cu alloys quantitatively and precisely while accounting for specific orientation distribution and spatial distribution. [ABSTRACT FROM AUTHOR]

Binary Al–Cu alloy has always been used to illustrate the phenomenon of precipitation hardening. Meanwhile, Al–Cu alloy has good heat resistance and is a potential heat-resistant conductor material, but there is not much research work on its electrical properties. In this work, the residual resistivity variation of Al-4Cu alloy at different aging stages was investigated. At the aging temperature of 160 °C, the residual resistivity of the Al-4Cu alloy decreases with the longer aging time, and it decreases rapidly in the early stage and slowly in the later stage, mainly due to the precipitation of solid solution Cu atoms and the interface electron scattering effect of different precipitates. In the early stage, massive precipitation of Cu atoms from the matrix can effectively reduce the crystal lattice distortion of Al matrix and significantly decrease the residual resistivity. Specifically, the residual resistivity of Al-4Cu alloy that aged at 160 °C for 13 h is 3.353 μ Ω·cm, which is only 82.6% of that in the supersaturated solid solution state. In later stage of aging, the main change is the evolution of the precipitated phase, i.e., the gradual disruption of the coherent relationship between the second phase and the Al matrix. And the coherency-strain fields decrease gradually, which is also beneficial in decreasing the residual resistivity. The results show that Al–Cu alloys can also be a potential heat-resistant conductor material for the power transmission industry.