Stress relaxation and flow behavior of ultrafine grained AA 1050

Mohebbi, Mohammad Sadegh; Akbarzadeh, Abdolhamid; Yoon, Young-Ok; Kim, Shae-Kwang

doi:10.1016/j.mechmat.2015.06.001

Cited by 50 publications

(9 citation statements)

References 34 publications

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“…The assumption seems to be justified since the plastic strain induced by stress relaxation is small and is obeyed by many metals [ 32 ]. However, recently, the changes in σ i and ρ m during stress relaxation were found in some materials [ 33 , 34 ].…”

Section: Discussionmentioning

confidence: 99%

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Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel

Zhao

Liu

et al. 2022

Materials

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The effects of surface dissolution on dislocation activation in FeSi6.5 steel are quantitatively studied by analyzing the stress relaxation data using the thermal activation theory of dislocation. The stressed FeSi6.5 steel sample in acid solutions (H2SO4 or HCl) exhibits a much higher rate of stress reduction with time compared with that in air or deionized water. As the stress relaxation time is prolonged to 20 min, the relaxation rates are 0.055 MPa·min−1 in water and 0.074, 0.1, 0.11 MPa·min−1 in H2SO4 solutions with pH 4, 3, and 2, respectively. In a NaCl solution, a slight increase in the relaxation rate compared with air was found. Higher acidity (lower pH) of the solution inducing higher stress relaxation rate implies the softening is associated with the anodic dissolution of the surface layer and the accelerated (additional) flow of dislocations. The analyses using the thermal activation theory of dislocation during relaxation reveal the mechanism for the accelerated plastic flow induced by the corrosive medium. The variations of these parameters are related to the relaxation of the stress field of dislocations and the weakening of interaction between slip dislocations and short-range obstacles. The chemomechanical effect, including a reduction in apparent activation energy and a decrease in waiting time for dislocation to obtain sufficient thermal activation energy to cross obstacles, causes an increase in the stress relaxation rate (plastic strain rate). The study confirms that surface dissolution accelerates the plastic flow of metals and supports the view that surface dissolution facilitates dislocation slip. It is helpful to improve the formability of brittle metals.

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Section: Discussionmentioning

confidence: 99%

“…In this work, the change of ρ m is investigated by the method used in [ 34 ]. Taking the logarithm of Equation (6), we get

…”

Section: Discussionmentioning

confidence: 99%

Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel

Zhao

Liu

et al. 2022

Materials

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“…The decrease in dislocation density during stress relaxation qualitatively agrees with previous TEM observations. 21,22) However, the strain anisotropy parameter q may possibly change during stress relaxation. If this is the case, the results of Fig.…”

Section: Proposal Of Analysis Approach To Obtain a Nonarbitrariness Cmentioning

confidence: 99%

Determination Approach of Dislocation Density and Crystallite Size Using a Convolutional Multiple Whole Profile Software

et al. 2018

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Neutron diffraction profile analysis using the whole profile fitting method is useful for obtaining microscopic information on metallic materials. To determine an appropriate fitting approach for obtaining reasonable and non-arbitrary results, we applied diffraction line profile analyses using the Convolutional Multiple Whole Profile (CMWP) method to diffraction patterns obtained using the Engineering Materials Diffractometer (TAKUMI, BL19) at the Materials and Life Science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The tensile specimens of 780 MPa grade bainitic steel were uniaxially stretched until the plastic strain reached a value of 0.05. We performed CMWP analyses on the obtained diffraction patterns during tensile test with various initial parameters of dislocation density and crystallite size. These parameters were optimized in the fitting procedures to minimize the weighted sums of squared residuals (WSSRs). Following this approach, we found that unsuitable initial parameter values resulted in unreasonable convergence. Therefore, initial fitting parameters should be chosen to ensure that the initial profiles are as broad as possible. Reasonable results were obtained following this suggestive approach even when the strain anisotropy parameter is set to arbitrary values.

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“…Recently, a set of stress-relaxation tests (single and repeated stress-relaxation tests with transient or long-term holding of load) have been developed to determine the governing deformation mechanisms of metals [25][26][27]. Using these tests, thermally activated deformationrelated variables, such as activation volumes and activation energies under certain loading and temperature conditions have been obtained to reveal the detailed thermally activated dislocation mechanisms [28,29].…”

Section: Introductionmentioning

confidence: 99%

A New Method to Characterize and Model Stress-Relaxation Aging Behavior of Aluminum Alloys Under Age Forming Conditions

Shi

2022

Metall Mater Trans A

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A new method that utilises theories of thermally activated deformation and repeated transient stress-relaxation tests has been proposed and validated in this study for the characterisation and modelling of the stress-relaxation ageing (SRA) behaviour of aluminium alloys and its dependence on stress and temperature. Using the new method, key deformation-related variables, i.e. stress components, activation volume and energy, of the aerospace grade heattreatable aluminium alloy AA7B04 have been obtained as a function of ageing temperature (388, 413 and 438 K), stress (both elastic and plastic) and SRA time (up to 4 h). It has been found that the apparent activation energy Qa of the material remains constant in the elastic region but decreases with increasing strain in the plastic region, and also decreases with increasing temperature for all initial loading stresses. These characteristics contribute to a much higher degree of stress-relaxation in the plastic region and at higher temperatures than in the elastic region and/or at lower temperatures. The obtained changing activation volume V and Qa indicate that the deformation rate is controlled by forest dislocation interactions in the elastic region (V decreases from over 200b 3 to less than 100b 3 ), and by a cross-slip mechanism at high stress levels in the plastic region (V decreases to a few tens of b 3 ). Based on these theories and results, a novel and simple constitutive model has been proposed, with which the stressrelaxation behaviour of AA7B04 at different ageing temperatures (388 to 448 K), pre-loaded from elastic to plastic regions for up to 16 h has been successfully predicted. The proposed model eliminates the limitations of conventional SRA models which mainly deal with elastic loading and isothermal conditions, and provides a foundation to effectively predict the springback after advanced non-isothermal SRA forming of aluminium alloy structures in the aerospace industry.

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Stress relaxation and flow behavior of ultrafine grained AA 1050

Cited by 50 publications

References 34 publications

Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel

Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel

Determination Approach of Dislocation Density and Crystallite Size Using a Convolutional Multiple Whole Profile Software

A New Method to Characterize and Model Stress-Relaxation Aging Behavior of Aluminum Alloys Under Age Forming Conditions

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