Stress Relaxation in an AZ31 Magnesium Alloy

Published on Jan 1, 2011in Key Engineering Materials
· DOI :10.4028/WWW.SCIENTIFIC.NET/KEM.465.101
Pavel Lukáč31
Estimated H-index: 31
(Charles University in Prague),
Zuzanka Trojanová20
Estimated H-index: 20
(Charles University in Prague)
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Abstract
Stress relaxation tests have been used in order to determine parameters of a possible thermally activated process in AZ31 magnesium alloy. The samples were deformed at a constant initial strain rate of 6.7x10-5 s-1 at various temperatures between room temperature and 300 °C. Stress relaxation, i.e. a decrease in the stress with time, was measured at various stress levels and at various temperatures. An analysis of the stress relaxation curves enabled to estimate the internal stress as a function of the strain and the test temperature. It has been shown that the activation volume is a function of the effective stress independently of the deformation temperature.
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2010
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Magnesium alloys of AJ (Mg-Al-Sr) and AX (Mg-Al-Ca) series were deformed at temperatures between room temperature and 300°C. Stress relaxation tests were performed in order to reveal features of the thermally activated dislocation motion. The work hardening rate 0 = dσ/de decreases with increasing stress and temperature. Analysis of the θ-σ plots revealed the hardening and softening mechanisms operating during the deformation. Internal and effective components of the applied stress have been est...
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Phenomenological equations between dislocation velocity, effective shear stress, temperature, and pressure are presented. It is suggested that the term "activation volume" be properly assigned to the pressure dependence of dislocation velocity. Indirect methods of determining velocity–stress relations are reviewed, and a new method is introduced using the stress–time data in stress relaxation. Some results are reported for high-purity iron, LiF, and NaCl crystals. Phenomenological relations near...
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Logarithmic stress relaxation in polycrystalline magnesium of 99.999% purity was studied at strains of up to 4% at 77-295 °K. The energy barrier of 0.74 ± 0.05 eV, associated with the relaxation, was found to be numerically equal to that known to control the temperature dependence of the flow stress of magnesium single crystals in simple glide. The observations are explained on the assumption that the relaxation arises from residual glide of basal dislocations impeded by the frictional drag of e...
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Cited By3
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Last. Sean R. AgnewH-Index: 55
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#1Vikaas Bajikar (UVA: University of Virginia)H-Index: 1
#2Jishnu J. Bhattacharyya (UVA: University of Virginia)H-Index: 12
Last. Sean R. Agnew (UVA: University of Virginia)H-Index: 55
view all 4 authors...
It is of interest to assess the thermally activated nature of the deformation mechanisms responsible for the anisotropic response of textured Mg alloys, especially in those alloys that do and do not contain rare earth elements. The repeated stress relaxation method in combination with elasto-viscoplastic self-consistent (EVPSC) polycrystal modeling is employed to determine the strain rate sensitivity and true activation volume of samples of textured, polycrystalline Mg alloys, ME10 and AZ31, loa...
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#1W Tang (UIUC: University of Illinois at Urbana–Champaign)H-Index: 1
#2K. L. Halm (UIUC: University of Illinois at Urbana–Champaign)H-Index: 1
Last. Armand Joseph Beaudoin (UIUC: University of Illinois at Urbana–Champaign)H-Index: 34
view all 7 authors...
Abstract The micro-plasticity of the Mg alloy AZ31 is explored through high-energy X-ray diffraction (HEXD). Through cyclic loading of the sample, a softening response is found to follow the resolved shear stress for basal slip. Stress relaxation is studied by applying an incremental elongation increase while continuously collecting images from a detector array. The rate exponent associated with a particular reflection is developed by evaluating the average lattice strain in the loading directio...
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