Al Zn Research Articles

Effect of retrograssion and re-aging on microstructure and properties of Al–Zn–Mg–Cu–Zr–Er alloy

Effect of retrograssion and re-aging on microstructure and properties of Al–Zn–Mg–Cu–Zr–Er alloy

Precipitate-mediated fatigue crack propagation behavior of Al–Zn–Mg–Cu alloy tailored by non-isothermal aging

The fatigue crack propagation behavior of non-isothermally aged Al–Zn–Mg–Cu alloy was examined at different aging stages. It has been revealed that non-isothermal aging (NIA) improved the fatigue crack resistance by adjusting the thermodynamics, and thus modified the precipitation configuration. Enhanced crack propagation threshold and decreased crack propagation rate were achieved when NIA was applied and carried out thoroughly. Fine and dispersed GP zones existing in underaged alloy significantly intensified the slip localization, which effectively mitigated the stress concentration near the crack tip and showed an approximately 8.2 MPa·m1/2 crack propagation threshold. Smaller width of the precipitate-free zone enabled the slip bands to propagate through the grain boundaries. However, relatively low strength and intense slip localization led the fatigue crack to propagate along the crystallographic slip bands, responsible for the higher crack propagation rate. For minorly over-aged alloys, coarsening and elevated number density of intragranular precipitate effectively hindered the movement of dislocation around, where strain concentration was frequently and preferentially induced, causing the degradation of resistance to fatigue crack propagation.

Optimizing the Zn and Mg contents of Al–Zn–Mg wrought alloys for high strength and industrial-scale extrudability

High-strength Al alloys of the 7xxx series are promising candidates for further light-weighting of car bodies. However, they are difficult to process by extrusion: complex geometries in particular pose a major challenge due to high extrusion pressures and tool wear. In addition to process optimization, alloy chemistries can be tailored for properties such as good extrudability or high strength. In this work, several experimental alloys based on EN AW 7108A were investigated with respect to the contents of the main alloying elements Zn and Mg, as well as heat treatment (e.g., homogenization), to achieve good extrudability and favourable mechanical properties. The experimental alloys were initially extruded on a small-scale extrusion press and evaluated with regards to their warm formability, microstructure, extrudability, and mechanical properties in T5 temper. Alloy compositions with Mg contents <1.2 wt.-% are optimal and lead to good extrudability as well as high yield strengths well above 350 MPa. The Zn content, on the other hand, has minor influence on the extrudability, but significantly increases strength at higher contents (∼60 MPa). However, the combined Zn + Mg content should not exceed 7 wt.-%. Based on these findings, two optimized alloys were designed, direct chill cast on industrial scale, and extruded on an industrial extrusion press. The alloys showed good extrudability and high strength in the T5 condition. The results also reveal that the limits of the EN AW 7108A alloy are exhausted and higher strengths could only be achieved with the optimized EN AW 7003 alloy.

Investigation of constitutive models and microstructure evolution during hot deformation and solution treatment of Al–Zn–Mg–Cu alloy

In this paper, isothermal thermal compression tests were carried out on Al–Zn–Mg–Cu alloys at varying deformation temperatures (360°C∼440°C) and strain rates (0.001s−1∼10s−1) using a Gleeble-3500C thermal simulation tester. Based on the true strain stress data obtained from the tests, the flow behavior of Al–Zn–Mg–Cu alloys during thermal deformation was investigated. Through a comprehensive consideration of deformation temperature, strain rate, and strain compensation, a high-precision constitutive model was established. Additionally, the specimens subjected to hot compression were further treated with solution annealing for different durations (0 h–2 h) to investigate the static recrystallization (SRX) behavior and the associated microstructural evolution of the alloy during the solution treatment process. Electron Backscatter Diffraction (EBSD) was employed to characterize the microstructure evolution of Al–Zn–Mg–Cu alloy under various deformation and solution treatment conditions. The EBSD data were further processed and analyzed using the MTEX toolbox. The results revealed that dynamic recovery (DRV) is the predominant softening mechanism during the deformation process, accompanied by a small amount of dynamic recrystallization (DRX). The dynamically recrystallized grains exhibit a random crystallographic orientation. Further investigation showed that low temperature and high strain rate conditions are unfavorable for the occurrence of dynamic recovery and dynamic recrystallization during the thermomechanical processing. However, dislocations accumulated during deformation provided sufficient stored energy for the growth of static recrystallized grains during subsequent solution treatment, with static recrystallized grains predominantly forming at grain boundaries.

Alternating Cu segregation and its stabilization mechanism for coherent [formula omitted] precipitates in Al–Zn–Mg–Cu alloys

The 7000 series (Al–Zn–Mg) Al-alloys are renowned for their exceptional “lightweight-high strength” properties, primarily owing to nano-sized meta-stable η′ precipitate as the main strengthening phase. However, these η′ precipitates are susceptible to transforming into the stable η2 phase at elevated temperatures, resulting in a decline in strength. To mitigate this, Cu-segregation has been long proposed as a promising method for stabilizing these meta-stable precipitates. However, the mechanisms involved have not been fully understood. In this study, we conducted a thorough investigation on the structural and energetic changes between Cu-free and Cu-segregated η' and η2 precipitates. Utilizing DFT calculations and HAADF-STEM characterizations, we uncovered a distinctive alternating Cu-segregation pattern. This pattern induces significant structural modifications within the bulk of η' precipitates and at the precipitate-matrix interface, markedly enhancing their interfacial and bulk energetics. We believe these modifications are the key factor in improving precipitate stability. Based on our findings, the underlying mechanism of solute segregation was elucidated and a novel strategy for optimal design of Al–Zn–Mg alloys was proposed.

Tracking microstructural evolution and hardening in Al–Zn–Mg–Cu alloys aged artificially via electrical conductivity measurements

Precipitation hardening, a crucial mechanism for strengthening aluminum alloys, involves stages like Guinier–Preston (GP) zone formation, precipitation, peak aging, and precipitate coarsening. This study focuses on the aluminum 7050 alloy, proposing a method to gauge artificial aging through electrical conductivity measurement. The evolving microstructure and time to peak hardness during aging are vital for creating high-strength alloys. The electrical conductivity variation over time is utilized to analyze the diffusion process governing the clustering and growth of specific phases (η′, η, and S) during artificial aging. The paper demonstrates the impact of GP zones, precipitate formation, and grain growth on electrical conductivity, correlating these factors with hardness, microstructure, and tensile strength to determine the hardening stage. Differential electrical conductivity plots, highlighting aging stages, assist in identifying the hardening phase. Tensile strength and hardness plots differentiate the precipitation phases. The Johnson–Mehl–Avrami–Kolmogorov equation models particle growth kinetics, determining growth rates for AA 7050 alloy. The overall activation energy for precipitate growth is 40.77 kJ/mol, with a growth constant ( m) of ∼4, indicating S phase nucleation during η′ and η growth.

Electrical and mechanical behaviors of rubber composites based on polar elastomers with incorporated Cu-based alloy

Dielectric elastomers with conducting inorganic fillers offer a wide range of uses, including capacitive energy storage, elastomer sensors, actuators, and many more. In this approach, low dielectric loss and high dielectric constant may be made possible by ternary composites that use metal alloy components as reinforcing fillers. Here, Cu-based alloy was added to acrylonitrile-butadiene rubber (NBR) to produce ternary rubber composites. Unfortunately, the Cu–Al–Zn alloy’s material incompatibility with the rubber matrix typically leads to phase separation, void formation, and particle aggregation, all of which have a dramatic negative impact on performance. Using 3-(trimethoxysilyl)propyl methacrylate as a coupling agent, Cu–Al–Zn alloy particles were uniformly dispersed onto the NBR rubber matrix through surface modification. By using scanning electron microscopy, the appropriate reinforcement of modified Cu-based alloy particles into NBR was carefully examined. The effect of modified Cu–Al–Zn alloy loading on the swelling behavior of the composite was also investigated. The findings show that the shape and dispersion state of modified Cu–Al–Zn alloy were important for the dielectric characteristics of the NBR compounds. By adding reinforced modified Cu-based alloy to the NBR matrix, mechanical characteristics were significantly improved. The uniform dispersion of modified Cu–Al–Zn alloy particles and strong interfacial compatibility with rubber matrix are the reasons for the outstanding performance of NBR composites, which suggests high-performance dielectric composite.

Effect of Extrusion Temperature on Microstructure and Mechanical Properties of Mg–Al–Zn Alloy Prepared by Solid‐State Recycling of Mixed Waste Chips

The recycled Mg–Al–Zn alloys are successfully fabricated through solid‐state recycling of mixed waste chips, including cold pressing and hot extrusion. The effects of extrusion temperature on the microstructure evolution, slip mode, tensile properties, and hardness are studied. The homogeneous fine dynamic recrystallization (DRXed) grains with an average grain size of less than 13.1 μm can be obtained at four different extrusion temperatures (250, 300, 350, and 400 °C). The average grain size of the DRXed grains continuously increases with the rising extrusion temperature. However, the yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (EL) of the recycled alloys increase first and then decrease. The recycled Mg–Al–Zn alloys at 350 °C demonstrate excellent mechanical properties with the YS of 134.6 MPa, UTS of 286.2 MPa, EL of 7.4%, and Vickers hardness of 75.2 HV, respectively. In addition, the slip mode is transformed from the previous basal slip to the coactivation of multiple slips composed of the basal slip, prismatic slip, and pyramidal slip with the rising extrusion temperature.

Strain Hardening in Dilute Binary Al–Cu, Al–Zn, and Al–Mn Alloys: Experiment and Modeling

During thermo-mechanical processing, dissolved alloying elements have a huge impact on the microstructure evolution by influencing the overall dislocation storage rate. Especially, for non-heat treatable Al alloys, the effects of strain-hardening and solid solution strengthening are of significant practical interest. In the present work, a detailed study of the room temperature work-hardening behavior of binary Al–Cu, Al–Zn, and Al–Mn alloys with varying solute concentrations is carried out. Stress–strain curves at different strain rates are recorded and computationally analyzed by an advanced 3-Internal-Variables-Model (3IVM) approach for the dislocation density evolution. The initial strengthening rate is examined as a function of the solute concentration.

Microstructure and Mechanical Properties of Al–Zn–Mg–Ni–Fe Alloy Processed by Hot Extrusion and Subsequent Radial Shear Rolling

Microstructure and Mechanical Properties of Al–Zn–Mg–Ni–Fe Alloy Processed by Hot Extrusion and Subsequent Radial Shear Rolling

Increasing ductility beyond post-uniform deformation through Zn lamellae deformation in Al at room temperature

The Zn element precipitates during aging in the Al–Zn binary alloy. Increased Zn content and prolonged aging leads to discontinuous Zn precipitation. The addition of 2 wt% Cu to the Al-43 wt%Zn alloy accelerates this discontinuous precipitation, resulting in decreased thickness of Zn layers and inter-distance between them. This acceleration is attributed to the influence of Cu solutes on the Zn phase, thereby reducing the interface energy between Zn precipitates and the Al matrix. The Al–Zn–Cu alloy demonstrates exceptional behavior during tensile tests, displaying a simultaneous increase in tensile strength and ductility alongside an 75 % reduction in area at room temperature drawing. Notably, despite the drawn beyond uniform deformation limit, there is an observed increase in total elongation. Our demonstration highlights this phenomenon, attributing it to the sustained coherent interface between the Zn layer and the Al matrix, as well as the uninterrupted continuity of Zn layers during drawing.

Influence of Tool Probe Profiles on the Microstructure Evolution and Mechanical Properties of Al–Zn–Mg–Cu Alloy Friction Stir Weldment

Influence of Tool Probe Profiles on the Microstructure Evolution and Mechanical Properties of Al–Zn–Mg–Cu Alloy Friction Stir Weldment

Effect of Pre-Deformation on Precipitation in Al–Zn–Mg–Cu Alloy

AbstractIn this work, strengthening effects and evolution of precipitates in a pre-deformed Al–Zn–Mg–Cu alloy during ageing were investigated using Vickers hardness measurements, tensile tests, and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It was found that all cold rolled conditions had higher mechanical strength than the non-deformed condition for all ageing times and that this effect increases at higher deformation ratios. It was also found that the non-deformed condition has a higher age hardening response than that of the cold rolled conditions. A homogeneous precipitate distribution was observed in the non-deformed condition, while the cold rolled conditions contained non-uniformly distributed precipitates due to the introduced dislocations. This led to larger precipitate sizes and a reduction in the precipitate number densities in the pre-deformed conditions. HAADF-STEM analysis revealed differences in the fraction of different precipitate types between the non-deformed and the cold rolled conditions. η', η2, and disordered η phase were observed in the non-deformed condition, while η', η2 and the newly identified Y phase were observed in the cold rolled conditions. The disordered η phase contained structural units of the η1 phase and was associated with reducing the lattice misfit between this phase and the Al matrix. Formation of the Y phase was related to an accelerated nucleation rate in the regions of high dislocation density. Graphical abstract

Hot deformation mechanism of a rapidly-solidified Al–Zn–Mg–Cu–Zr alloy

This study systematically investigates the flow behavior of 7050 aluminum (Al) alloy produced via spray forming and subjected to a proposed pretreatment through thermal compression tests. The experimental findings reveal that the peak stress increased with decreasing deformation temperature or increasing strain rates. The parameters in the Arrhenius constitutive model were determined and verified by experimental results for spray formed (SFed) 7050 Al alloy. Hot deformation activation energy of the SFed 7050 Al alloy (147.38 kJ/mol) is notably lower than that of cast Al–Zn–Mg–Cu–Zr alloys, which is attributed to factors such as fine grains, low segregation, pores, and dispersed Al3Zr induced by pretreatment. Furthermore, processing maps have been constructed at various strains, revealing optimal stable deformation conditions at 300–450 °C/0.001–0.15s−1 and 425–450 °C/0.2–1s−1. Microstructural analysis of deformed samples highlights the critical role of dynamic recrystallization in influencing the stable and unstable areas of the alloy, which may be activated by high temperature and slow strain rate. The hot deformation mechanism of the SFed Al alloy is governed by interactions among η-Mg(Zn,Al,Cu)2 precipitates, dispersed Al3Zr particles, dislocation structures, and (sub-)grain boundaries.

Effect of non-isothermal retrogression and re-aging treatment on microstructure evolution and mechanical properties of Al–Zn–Mg–Cu alloy

The mechanical properties of rolled 7075 aluminum alloy treated by non-isothermal retrogression and re-aging can exceed the traditional peak aging (T6) and isothermal retrogression and re-aging. After non-isothermal retrogression and re-aging (NIA 180/60) treatment, compared with the T6 state alloy, the alloy has obvious grain boundary precipitate-free zone, and the tensile strength is increased from 558 ± 1.2 MPa to 611 ± 1 MPa. The main mechanism leading to the increase of mechanical properties is precipitation strengthening, followed by grain boundary strengthening, which is not related to crystal orientation, dislocation strengthening and solid solution strengthening. During the non-isothermal retrogression and re-aging treatment, the partial dissolution of the existing precipitates (GP zone and η′ phase), the growth of the remaining precipitates and the precipitation of new η′ phase, as well as the secondary precipitation in the re-aging stage, lead to the increase of the size and density of the intragranular precipitates compared with the T6 state alloy, and the maximum precipitation strengthening effect is obtained. This paper also discusses the relationship between performance changes and microstructure, which can provide a reference for optimizing the regression re-aging process.

Investigation of deformation behavior and strain-induced precipitations in Al–Zn–Mg–Cu alloys across a wide temperature range

This study explores the hot deformation behavior of Al–Zn–Mg–Cu alloy through uniaxial hot compression (200 °C–450°C) using the Gleeble-1500. True stress–strain curves were corrected, and three models were established: the Arrhenius model, strain compensated (SC) Arrhenius model, and strain compensated recrystallization temperature (RT) segmentation-based (TS-SC) Arrhenius model. Comparative analysis revealed the limited predictive accuracy of the SC Arrhenius model, with a 25.12% average absolute relative error (AARE), while the TS-SC Arrhenius model exhibited a significantly improved to 9.901% AARE. Material parameter calculations displayed variations across the temperature range. The SC Arrhenius model, utilizing an average slope method for parameter computation, failed to consider temperature-induced disparities, limiting its predictive capability. Hot processing map, utilizing the Murty improved Dynamic Materials Model (DMM), indicated optimal conditions for stable forming of the Al–Zn–Mg–Cu alloy. Microstructural analysis revealed MgZn2 precipitation induced by hot deformation, with crystallographic defects enhancing nucleation rates and precipitate refinement.

The phase transformation and enhancing mechanical properties in high Zn/Mg ratio Al–Zn–Mg–Cu(-Si) alloys

Aging behavior and phase transformation of Al–5Zn–1Mg–1Cu(-Si) alloys under different isothermal temperatures were investigated using transmission electron microscope (TEM) and mechanical tests. The aging temperature and Si addition significantly influenced to the types of precipitated phases and mechanical properties of the Al–Zn–Mg–Cu alloys. Adding Si in this alloy changed the precipitated phases from T′ and η′ phases to the dual-sized η and GPB-II phases. With increasing isothermal aging temperature, more GPB-II phases formed in alloys with the same composition, effectively improving the microhardness and mechanical properties. When aging at 150 °C, 0.5 wt%Si-containing alloy reached the highest peak hardness of about 150HV and maintained stable hardness, while an alloy without Si only reached 120HV and later declined by 15HV. The tensile strength and yield strength of the 0.5 wt%Si-containing alloy were higher than those of non-Si alloy by 132 MPa and 165 MPa, increasing 51% and 90%, respectively. This result was due to the presence of fine and dispersed 4–8 nm GPB-II phases in 0.5 wt%Si-containing alloy. The GPB-II phase had a core-shell structure, with the core region mainly enriched in Mg and Si, and the shell region mainly enriched in Cu and Zn. Compared with the stability of T′ and η′ phases, this core-shell structure of GPB-II effectively inhibited its growth and beneficially maintained a smaller-sized GPB-II phase. The strengthening effect of GPB-II phase was better than that of η or T phases when aging at 150 °C or 200 °C. The mechanical properties of high Zn/Mg ratios Al–Zn–Mg–Cu alloys can enhanced by adding Si.

Effect of TiB2 particles on dynamic recrystallization in TiB2-reinforced Al–Zn–Mg–Cu–Zr during hot compression

We investigated the microstructure evolution of a 6 wt% TiB2-reinforced Al–Zn–Mg–Cu–Zr composite subjected to hot compression at temperatures within the range 370 °C–490 °C, at strain rates between 0.001 s−1 and 10 s−1. The microstructure evolution was characterized by electron backscatter diffraction and transmission electron microscopy. Dynamic recovery and dynamic recrystallization mechanisms were analyzed, with a focus on nucleation at original grain boundaries and TiB2 particles. The results show that recovery is the main dynamic softening mechanism due to the high dislocation mobility in the Al matrix. However, low temperature and high strain rate results in a large number of small recrystallized grains, whereas high temperature and low strain rate results in a few large recrystallized grains. Dynamic recrystallization is mainly attributed to particle-stimulated nucleation occurring near TiB2 particles/clusters, especially TiB2 particles/clusters at grain boundaries. Relations between the observed dynamic recrystallization and the Zener-Hollomon parameter are discussed.

Fatigue crack propagation anisotropy of an Al–Zn–Mg–Cu super-thick plate

The fatigue crack propagation (FCP) rate is an important performance index in the aerospace industry for the safe lifespan evaluation. In this study, the FCP anisotropy of an Al–Zn–Mg–Cu super-thick rolled plate was analyzed. The results show that as the depth increases, the FCP anisotropy gradually becomes significant especially in the low ΔK region. The specimens tested along the transverse direction exhibit lower FCP rate than those tested along the rolling direction in the low ΔK region, which is related to the difference in the grain shape and grain orientation. More specifically, the crack is easy to deflect along the grain boundaries in the deformed grains when loading along the transverse direction. Meanwhile, more obvious grain orientation deviation on both sides of the crack can cause larger angle deflection, longer FCP path, and lower FCP rate. In the Paris region, the FCP anisotropy is not obvious regardless of thickness. The reason is that the main influencing factor is controlled by strength in this region, while the strength anisotropy is very limited leading to this similarity.

Effect of deep cryogenic treatment on improving the high-temperature impact resistance of Al–Zn–Mg–Cu alloy

The aging Al–Zn–Mg–Cu alloy exhibits a significant decrease in performance after undergoing thermal shock. In order to improve the resistance of this type of alloy to thermal shocks, the influence of deep cryogenic treatment (DCT) on the high temperature mechanical properties and microstructure of thermal shocked Al–Zn–Mg–Cu alloy is investigated in this paper. It was found that the mechanical properties of Al–Zn–Mg–Cu alloys decrease significantly with the increase of electric heating temperature. The deep cryogenic treatment reduced the grain size of Al–Zn–Mg–Cu alloy, increased the density of the precipitates, and also inhibited the coarsening of the precipitates. Therefore, the deep cryogenic treatment can slow down the weakening effect of Al–Zn–Mg–Cu alloy at high temperatures.