Work-hardening behaviour of a heat-treatable AA7108 aluminium alloy deformed to intermediate strains by compression (original) (raw)
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Simple constitutive analysis of AA 7075-T6 aluminium alloy deformed at low deformation temperatures
Materials Science and Technology, 2012
The tensile stress-strain behaviour of AA 7075-T6 aluminium alloy deformed at temperatures in the range of 123-248 K, at strain rates between 0?0023 and 0?21 s 21 has been analysed in order to develop a rational constitutive description of the material under such deformation conditions. The constitutive formulation has been derived on the basis of the mechanical threshold stress model developed at Los Alamos National Laboratory. The constitutive equation thus proposed is able to separate the contribution of the different components that give rise to the mechanical strength of the alloy. It has been determined that the flow stress of the material arises mainly from the contribution of three different components: athermal barriers to dislocation motion, solid solution and precipitation hardening and work hardening (dislocation-dislocation interaction). The flow stress in each strain increment during the course of plastic deformation is computed recursively from its previous value, before the updating of the deformation temperature and strain rate values. Such a computation is carried out by the numerical integration of the phenomenological work hardening law expressed in differential form. The constitutive description thus proposed provides an accurate prediction of the experimental values of both the flow stress and work hardening rate of the material. Moreover, its formulation in differential form provides a reasonable description of the stress changes that could take place when arbitrary temperatures and strain rate paths are imposed to the material during plastic deformation. It is shown that the formulation is general enough for describing also the constitutive behaviour and stress changes of a different aluminium alloy deformed under hot working conditions, where the material exhibits positive work hardening before achieving saturation at large strains.
Influence of heat treatment on the cyclic deformation properties of aluminium alloy AA7030
Materials Science and Engineering: A, 2008
An extruded AA7030 alloy (Al-5.4Zn-1.2Mg) was tested in low-cycle fatigue at different total strain amplitudes to determine the cyclic deformation and fracture behaviour and to investigate the effect of heat treatment-natural ageing (NA) or peak ageing (PA). The results show that the fatigue life is longer in the NA temper at a given plastic strain amplitude. The fatigue life can be described by a total strain amplitude approach, where both NA and PA fall on the same straight line. The NA temper shows continuous cyclic hardening until the onset of fatal crack growth while the PA temper hardens during the first 20-30% of the fatigue life and then softens due to crack growth. The crack propagation mechanisms are different between the tempers, where NA favours transgranular cracking while intergranular propagation prevails in PA. Finally, a tension/compression stress asymmetry was observed under symmetric straining.
Precipitation, strength and work hardening of age hardened aluminium alloys
IOP Conference Series: Materials Science and Engineering, 2015
The strength and work hardening of age hardened AA6063 and AA6082 alloys have been investigated in terms of a detailed characterization of precipitate and dislocation structures obtained by TEM and SEM. Tensile and compression tests were performed at as quenched, peak aged and severely aged conditions. A strong work hardening in the as quenched condition was found, similar to AlMg alloys with twice as much alloying elements in solid solution. It was found that the initial work hardening rate and the critical failure strain are both smallest at the peak aged condition. During large deformations the needle-shaped precipitates are sheared uniformly by dislocations altering their <001> orientations, which indicates extensive cross slip. In the overaged condition the early initial work hardening is larger than at the peak aged condition, but followed by a weak linear work hardening, apparently directly entering stage IV at a low strain. Cracked, needle-shaped precipitates were seen at larger strains.
Work hardening and plastic anisotropy of naturally and artificially aged aluminium alloy AA6063
Mechanics of Materials, 2019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights Tensile tests in different material directions are performed for different tempers of an extruded AA6063 alloy A variation in stress ratio and strain ratio are observed in 0° and 45° directions The microstructure evolution during the heat treatment of the alloy is modelled The microstructural parameters are correlated to the variations in the stress and strain ratio The possible explanations for the stress ratio variations are analysed
High-Temperature Deformation of Naturally Aged 7010 Aluminum Alloy
2021
This study is focused on the deformation mechanism and behavior of naturally aged 7010 aluminum alloy at elevated temperatures. The specimens were naturally aged for 60 days to reach a saturated hardness state. High-temperature tensile tests for the naturally aged sample were conducted at different temperatures of 573, 623, 673, and 723 K at various strain rates ranging from 5 × 10−5 to 10−2 s−1. The dependency of stress on the strain rate showed a stress exponent, n, of ~6.5 for the low two temperatures and ~4.5 for the high two temperatures. The apparent activation energies of 290 and 165 kJ/mol are observed at the low, and high-temperature range, respectively. These values of activation energies are greater than those of solute/solvent self-diffusion. The stress exponents, n, and activation energy observed are rather high and this indicates the presence of threshold stress. This behavior occurred as a result of the dislocation interaction with the second phase particles that are ...
Temperature and Strain Rate Effects on the Dynamic Strain Ageing of Aluminium Alloy AA7030
Materials Science Forum, 2006
The effects of temperature and strain rate on the mechanical properties of aluminium alloy AA7030 (Al-5.4Zn-1.2Mg) in naturally aged and peak aged condition are investigated, with emphasis on the relation to dynamic strain ageing. It is found that the naturally aged material shows more severe signs of dynamic strain ageing, including inverse strain rate and temperature dependence of flow stress, inverse temperature dependence of the ductility and serrated yielding. The peak aged material also shows signs of dynamic strain ageing, but to a lesser extent, most pronounced through serrated yielding. The observed effects can be qualitatively explained in terms of a thermal activation based model for dislocation glide. Furthermore, inhomogeneous deformation is observed on several size scales ranging from localized glide bands to surface deformation effects (orange peel surface) and macroscopic flow localization in shear bands.
2021
The hot deformation behavior of the heat-treated AA6061 and AA 6063 aluminum alloys by T6-1, T6-2 artificial aging treatment, and O annealing treatment were studied by compression testing over a temperature range of 350–550°C and strain rates of 0.005-0.1 s-1. It was observed that the flow stresses of the studied aluminum alloys treated by the T6-1 and T6-2 heat treatments were significantly higher than those of the O annealing treatment. Moreover, the stress-strain curves of the heat-treated alloys by the T6-1, T6-2, and O heat treatments demonstrated significant softening during deformation at the lowest strain rate under any of the deformation conditions. For several strains, the activation energy of hot deformation was specified and obtained to vary significantly with strain for the heat-treated alloys by the T6-1 and T6-2 treatments. The stress-strain data calculated from a linear equation, with strain-dependent parameters, shows a great fit with the experimental data for the h...
Development of mechanical properties during secondary aging in aluminium alloys
Materials Science and Technology, 2005
Earlier work has shown that, if the artificial aging of aluminium alloys is interrupted by a dwell period at lower temperature, higher values of tensile properties and fracture toughness may be achieved than are possible with single stage T6 tempers. A second interrupted aging cycle has now been developed that involves underaging at the elevated temperature, quenching, and then allowing secondary precipitation to occur at, or just above, room temperature. Designated a T6I4 (I5interrupted) temper by the authors, this simpler aging cycle may reduce heat treatment costs. Tests on some 30 cast and wrought alloys have resulted in tensile properties close to those for a T6 temper, with higher values of fracture toughness being recorded for some cases. Such an aging treatment can be incorporated into a paint bake cycle to simplify the heat treatment of coated automotive components.
Materials today communications, 2021
The effect of pre-stretching on the mechanical behaviour of the aluminium alloys AA6063, AA6061 and AA6110 in temper T6 has been investigated. Uniaxial tensile tests and quasi-static axial crushing tests were conducted on rectangular hollow section (RHS) profiles pre-stretched 0.5 % and 4.0 % prior to artificial ageing. The stressstrain curves from the uniaxial tensile tests with different pre-stretching levels were used to investigate the effect of pre-stretching on the mechanical behaviour. It was found that the yield stress and ultimate tensile stress were somewhat lower and the failure strain was considerably higher for the profiles pre-stretched 4.0 % compared to those pre-stretched 0.5 %. In the crushing tests, less cracks were generally seen by visual inspection on the profiles pre-stretched 4.0 % but the specific energy absorption was slightly lower for these profiles. The nanostructure model NaMo was used to predict the stress-strain curves and the results were compared to the experimental data. Overall, the experimental trends were accurately predicted by NaMo, even though the hardening stagnation observed predominantly for profiles pre-stretched 4.0 % was not captured. The predicted evolution of the microstructure during artificial ageing was used to gain insight into the physical mechanisms responsible for the observed stress-strain behaviour.
Effect of Solution Heat Treatment and Artificial Aging on Compression Behaviour of A356 Alloy
Materials Science, 2019
Aluminium alloys are subjected to heat treatment to increase the strength and corrosion properties. This paper aims to study the effect of heat treatment on the compression behaviour of A356 alloy under quasi static condition and barreling effect. The various heat treatments are: (i) solution heat treatment of 1 h at 540 °C + natural aging 0 h + artificial aging at 180 °C up to 5.5 h, (ii) solution heat treatment of 3 h at 540 °C + natural aging for 20 h + artificial aging at 180 °C up to 5.5 h, and (iii) solution heat treatment of 6 h at 540 °C + natural aging for 20 h + artificial aging at 180 °C up to 5.5 h. Specially to understand the influence of artificial aging at every 0.5 h up to 5.5 h, the specimens were heat treated. From the results, solutionizing for 1 hr have a better compression strength irrespective of the artificial aging. Natural aging had decreased the ductility but increased the strength property. Artificial aging had a significant effect on the compressive stren...