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Journal ArticleDOI: 10.1016/J.JALLCOM.2020.158180

Mechanical properties of solution heat treated Al-Zn-Mg-Cu (7075) alloy under different cooling conditions: Analysis with full field measurement and finite element modeling

05 Mar 2021-Journal of Alloys and Compounds (Elsevier)-Vol. 856, pp 158180
Abstract: The effect of W-temper heat treatment, consisting of solution heat treatment (SHT) and rapid cooling, on the mechanical properties and fracture of high strength aluminum alloy 7075 sheet is investigated experimentally and numerically. Three different cooling conditions from the solution heat treated as-received T6 temper 7075 alloy sheet are considered: water quenching, die quenching, and air cooling. The mechanical properties are measured by uniaxial tensile tests and limiting dome height (LDH) formability tests on the heat treated samples. Moreover, the distributions of strain and strain rate are analyzed by the full-field digital image correlation (DIC) technique, which enables the quantitative investigation on the Portevin–Le Chatelier (PLC) band propagations induced by dynamic strain aging (DSA). The DIC analysis reveals the distinctive formability between uniaxial and biaxial tensile stress states of the W-temper samples. In the finite element analysis, the hardening model based on Kocks-Mecking-Estrin-McCormick (KMEC) model is employed to incorporate the DSA-originated PLC band propagation in the simulation of LDH formability test. The simulated LDHs agree well with experiments when the PLC effect along with planar anisotropy of the heat treated 7075 alloy sheets is properly implemented.

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Topics: Dynamic strain aging (58%), Formability (54%), Strain rate (53%) ... show more

9 results found

Journal ArticleDOI: 10.1016/J.JMATPROTEC.2021.117211
Abstract: Influence of tempers on the hole-expansion formability of an AA7075 aluminum sheet is investigated for -T6 (as-received) and -W tempers (super saturated by the solution heat treatment followed by water quenching). The hole is prepared by end-milling, to limit the effects of hole preparation on the results and instead highlight the effects of material behavior. A flat-headed punch is used to expand the hole, and digital image correlation captures the strain fields throughout the experiment. The results present that the hole can expand by 70 % more in -W compared to -T6 temper with the lower forming force. In contrast, thickness strain distribution around the hole shows a similar pattern in both tempers except the observation of Portevin-Le Chatelier (PLC) effect in -W temper, which causing the inhomogeneous deformation. In parallel, the numerical simulation of the hole-expansion is performed using a user material subroutine implemented for the elasto-plastic material behavior, including plastic anisotropy, of both tempers. The predictions on the thickness strain variation and average level show good agreement with the experiment for -T6 temper, but less so for -W temper. This is shown to be the effect of PLC bands on the deformation: the material in -T6 temper is mainly governed by plastic anisotropy, but -W temper shows combined effect of plastic anisotropy and PLC bands. Nevertheless, the reasonable predictions of both tempers verify that the numerical framework established in this study can be used for preliminary, computationally-efficient virtual process design with a practical purpose, despite omitting the explicit physics of the PLC effect.

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Topics: Formability (52%)

2 Citations

Journal ArticleDOI: 10.1016/J.JALLCOM.2021.160763
Yanwu Wang1, H.J. Jiang1, C.Y. Liu1, Hongfeng Huang1  +2 moreInstitutions (1)
Abstract: The Al particle reinforced 7075 Al matrix composites with the layered structure are prepared by hot rolling to improve the damping property of the alloy. Numerous interparticle interfaces are observed in the Al particle layer (reinforcement), and the traces of no interfacial reaction or elemental diffusion are found between the matrix and reinforcement layer. The tensile strength of the composite is 29% higher than that of the matrix. The internal friction values of the Alp/7075Al lamellar composite and the 7075 Al matrix are found to increase with the increase in temperature and strain, respectively. At 570 K, the internal friction values of the composites are found to be as high as 0.105, which is 337% higher than that of the matrix, and an internal friction peak (P2) appears in the composites due to the recrystallization of Al particles at high temperature. The comprehensive damping index of the composite is found to be about 2.9-fold of the 7075 Al matrix. The damping mechanism of the composite is mainly attributed to dislocation damping, grain boundary damping, and interface damping.

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Topics: Recrystallization (metallurgy) (52%), Composite number (52%), Grain boundary (51%) ... show more

1 Citations

Open accessJournal ArticleDOI: 10.1016/J.JMRT.2021.08.146
Yun Cheng1, Junhua Xu1, Lihua Yu1, Yunxuan Hu1  +2 moreInstitutions (1)
Abstract: Owing to the notorious hot-crack susceptibility and severe softening fusion-weld joints of Al–Zn–Mg–Cu alloys, they are generally considered unweldable. In this study, TiC/7xxx (TC) and TiC–TiB2/7xxx (BC) aluminum matrix composites, fabricated by in-situ mixed-salt reaction, were used as filler rods of spray formed 7055 alloys to modify the microstructure and mechanical properties of TIG weld joints. Compared with 7055-weld metal (WM), the grain sizes of TC-WM and BC-WM were refined from 100 μm to 24 μm and 26 μm, respectively. The precipitation of eutectic phases in WM was reduced by ceramic particles, which decreased the hot-crack susceptibility of joints. In the as-welded state, the ultimate tensile strength of TC and BC joints increased from 240 ± 5 MPa to 274 ± 5 MPa and 300 ± 5 MPa, respectively. The addition of ceramic particles also improved the impact toughness and hardness of weld joints. Grain refinement, load-bearing strengthening, coefficients of thermal expansion mismatch strengthening, and Zener pinning strengthening are the dominant strengthening mechanisms of weld joints with ceramic particles.

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Topics: Strengthening mechanisms of materials (55%), Zener pinning (53%), Ceramic (53%) ... show more

1 Citations

Open accessJournal ArticleDOI: 10.3390/MET11071111
12 Jul 2021-
Abstract: Aluminum alloy hot stamping technology can improve the formability of materials and obtain parts with high dimensional accuracy. Friction behavior in the hot stamping process is very important for forming quality. Accurate friction coefficient is helpful to improve the prediction accuracy of forming defects. It is hard to obtain the friction coefficient by simple experiments due to the complicated thermal–mechanical coupling and contact conditions during the hot stamping of aluminum alloys. In order to explore the effect of friction behavior on forming quality, hot stamping experiments of 7075 aluminum alloy U-shaped parts with different lubricants were carried out. The influence of different lubricants on the force–displacement curve, material inflow, surface appearance, and thickness distribution of the formed part was analyzed. The results showed that a good lubrication effect could be obtained with the molybdenum disulfide lubricant. The friction coefficient under different lubrication conditions was obtained by using the inverse problem optimization method. Compared with the experimental results, the determined friction coefficients could accurately predict the force–displacement curves and the thickness distributions of formed parts under different lubrication conditions.

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Topics: Hot stamping (64%), Lubrication (58%), Lubricant (55%) ... show more

Journal ArticleDOI: 10.1007/S11771-021-4669-Y
Cunguang Chen1, Weihao Han1, Miao Qi1, Shi-peng Dong1  +4 moreInstitutions (1)
Abstract: In this work, a novel ultrahigh-strength Al−10Zn−3.5Mg−1.5Cu alloy was fabricated by powder metallurgy followed by hot extrusion. Investigations on microstructural evolution and mechanical properties of the fabricated samples were carried out. The results show that the grain size of sintered samples matches with the powder particles after ball milling. The relative densities of sintered and hot extruded samples reach 99.1% and 100%, respectively. Owing to the comprehensive mechanism of grain refinement, aging and dispersion strengthening, the ultimate tensile strength, yield strength and elongation of the Al−10Zn−3.5Mg−1.5Cu alloy after hot extrusion and subsequent heat treatment achieve 810 MPa, 770 MPa and 8%, respectively.

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Topics: Powder metallurgy (60%), Ultimate tensile strength (56%), Extrusion (55%) ... show more


55 results found

Journal ArticleDOI: 10.1016/S0749-6419(02)00019-0
Frédéric Barlat1, Frédéric Barlat2, J.C. Brem2, Jeong W. Yoon1  +7 moreInstitutions (6)
Abstract: A new plane stress yield function that well describes the anisotropic behavior of sheet metals, in particular, aluminum alloy sheets, was proposed. The anisotropy of the function was introduced in the formulation using two linear transformations on the Cauchy stress tensor. It was shown that the accuracy of this new function was similar to that of other recently proposed non-quadratic yield functions. Moreover, it was proved that the function is convex in stress space. A new experiment was proposed to obtain one of the anisotropy coefficients. This new formulation is expected to be particularly suitable for finite element (FE) modeling simulations of sheet forming processes for aluminum alloy sheets.

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Topics: Plane stress (62%), Stress space (57%), Cauchy stress tensor (57%) ... show more

1,197 Citations

Journal ArticleDOI: 10.1016/J.MATDES.2013.12.002
Tolga Dursun1, Costas Soutis2Institutions (2)
01 Apr 2014-Materials & Design
Abstract: Aluminium alloys have been the primary material for the structural parts of aircraft for more than 80 years because of their well known performance, well established design methods, manufacturing and reliable inspection techniques. Nearly for a decade composites have started to be used more widely in large commercial jet airliners for the fuselage, wing as well as other structural components in place of aluminium alloys due their high specific properties, reduced weight, fatigue performance and corrosion resistance. Although the increased use of composite materials reduced the role of aluminium up to some extent, high strength aluminium alloys remain important in airframe construction. Aluminium is a relatively low cost, light weight metal that can be heat treated and loaded to relatively high level of stresses, and it is one of the most easily produced of the high performance materials, which results in lower manufacturing and maintenance costs. There have been important recent advances in aluminium aircraft alloys that can effectively compete with modern composite materials. This study covers latest developments in enhanced mechanical properties of aluminium alloys, and high performance joining techniques. The mechanical properties on newly developed 2000, 7000 series aluminium alloys and new generation Al–Li alloys are compared with the traditional aluminium alloys. The advantages and disadvantages of the joining methods, laser beam welding and friction stir welding, are also discussed.

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Topics: 5005 aluminium alloy (62%), Aluminium (62%), Friction stir welding (55%) ... show more

1,153 Citations

Journal ArticleDOI: 10.1002/PSSA.2210300120
Abstract: Dynamic strain aging (DSA) in solid solutions is described as diffusion of solute atoms to mobile dislocations, temporarily arrested at obstacles. As a consequence the solute concentration experienced locally by the dislocations depends on the time of arrest and the solute diffusion coefficient. Starting from this idea the dependence of the flow stress on strain rate, temperature, and strain in the presence of DSA is calculated. A criterion for the onset of serrated yielding is formulated. Finally the change in strain rate sensitivity due to DSA is calculated. The theory allows a qualitative and in some respects a quantitative comparison with experimental results of which some examples are given.

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Topics: Strain rate (59%), Dynamic strain aging (58%), Portevin–Le Chatelier effect (56%) ... show more

503 Citations

Open accessJournal ArticleDOI: 10.2320/MATERTRANS.L-MZ201132
Abstract: The main Aluminium applications as state-of-the-art in European cars are presented. The main established Aluminium alloys and their application in automotive parts are presented together with recent developments. Also new studies and innovative multi-material concepts are discussed where Aluminium light-weight solutions are compared with that of other materials, like new steels, magnesium, plastics and composites. In the “SLC” (Super-Light-Car) project these new concepts were tested in a multi-material body-in-white prototype for a VW Golf V car, reaching a 34% weight reduction within a cost increment of 7,8 €/kg saved, with suitable technologies for high volume assembly cycles. In the final SLC concept Aluminium is the material of choice, proving its leading role in innovative light-weighting of cars. Aluminium achieves weight savings of parts up to 50% while maintaining safety and performance in a cost efficient way, competing efficiently with other light-weight materials.

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Topics: Aluminium (55%)

296 Citations

Journal ArticleDOI: 10.1016/J.IJPLAS.2010.02.005
Abstract: An empirical plasticity constitutive form describing the flow stress as a function of strain, strain-rate, and temperature has been developed, fit to data for three dual-phase (DP) steels, and compared with independent experiments outside of the fit domain. Dubbed the ‘‘H/V model” (for ‘‘Hollomon/Voce”), the function consists of three multiplicative functions describing (a) strain hardening, (b) strain-rate sensitivity, and (c) temperature sensitivity. Neither the multiplicative structure nor the choice of functions (b) or (c) is novel. The strain hardening function, (a), has two novel features: (1) it incorporates a linear combination coefficient, a, that allows representation of Hollomon (power law) behavior (a = 1), Voce (saturation) behavior (a = 0) or any intermediate case (0 < a < 1, and (2) it allows incorporation of the temperature sensitivity of strain hardening rate in a natural way by allowing a to vary with temperature (in the simplest case, linearly). This form therefore allows a natural transition from unbounded strain hardening at low temperatures toward saturation behavior at higher temperatures, consistent with many observations. Hollomon, Voce, H/V models and others selected as representative from the literature were fit for DP590, DP780, and DP980 steels by least-squares using a series of tensile tests up to the uniform strain conducted over a range of temperatures. Jump-rate tests were used to probe strain rate sensitivity. The selected laws were then used with coupled thermo-mechanical finite element (FE) modeling to predict behavior for tests outside the fit range: non-isothermal tensile tests beyond the uniform strain at room temperatures, isothermal tensile tests beyond the uniform strain at several temperatures and hydraulic bulge tests at room temperature. The agreement was best for the H/V model, which captured strain hardening at high strain accurately as well as the variation of strain hardening with temperature. The agreement of FE predictions up to the tensile failure strain illustrates the critical role of deformation-induced heating in high-strength/high ductility alloys, the importance of having a constitutive model that is accurate at large strains, and the implication that damage and void growth are unlikely to be determinant factors in the tensile failure of these alloys. The new constitutive model may have application for a wide range of alloys beyond DP steels, and it may be extended to larger strain rate and temperature ranges using alternate forms of strain rate sensitivity and thermal softening appearing in the literature.

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Topics: Strain hardening exponent (66%), Strain rate (63%), Work hardening (61%) ... show more

292 Citations

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