Creep deformation behaviour of AZ31 magnesium alloy over wide range of temperature and stress

Abstract

The creep deformation behaviour of coarse grained AZ31 magnesium alloy was examined in the temperature range from 423 to 673 K (0?46-0?73T m ) under various constant stresses covering low strain rate range from 4610 29 to 2610 22 s 21 . Most shape of the creep curve was typical of class II behaviour. However, only at low stress and low temperature, the shape of the creep curve was typical of class I behaviour. At very low stress at 673 K, the stress exponent for the secondary creep rate was~2. At low stress level, the stress exponent was~3 and the present results were in good agreement with the prediction of Takeuchi and Argon model. At high stress level, the stress exponent was~5 and the present results were in good agreement with the prediction of Weertman model. The transition of deformation mechanism from solute drag creep to dislocation climb creep could be explained in terms of solute atmosphere breakaway concept.

Verification of Equation for Evaluating Dislocation Density during Steady-state Creep of Metals

“…Ishikawa, Watanabe, and Mukai (2005) reported similar creep data at 23 to 450 ℃. Among these data, the steady-state creep rates at temperatures higher than 300 ℃ obtained by Hyun and Kim (2014) are plotted as functions of stress in Figure A21. The indicated data were classified into Grs.…”

“…The referred creep data of HCP metals (Taira et al, 1960;Dragomir et al, 2005;Hyun et al, 2014;Roodposhti et al, 2015) do not contain any information on twinning deformation. Twinning should affect the values of through the temperature dependence of the strain rate, given by Equation 7, and the strain rate due to twinning directly affects the value of through Equation 13.…”

“…Mg alloy (HCP) Figure A21. Relations between stress and the creep rate in the steady state for AZ31 Mg alloy Hyun et al (2014). Creep data (solid diamond marks) (Roodposhti et al, 2015), the dislocation density obtained employing XRD analysis, and the calculated value of for each stress are also shown Fabian, Trojanova, and Kuzel (2007) reported the dislocation densities of pure Mg with ultra-fine grains smaller than 0.4 μm compressed at 23 to 200 ℃ employing XRD analysis and Matsunaga, Kameyama, Takahashi, and Sato (2009) reported the creep data of pure Mg with coarse grains of 120 μm.…”

“…They also confirmed that a basal plane slip was a major slip system. Hyun and Kim (2014) conducted creep tests of AZ31 Mg alloy with 48-μm grains at 150 to 400 ℃. Ishikawa, Watanabe, and Mukai (2005) reported similar creep data at 23 to 450 ℃.…”

High toughness magnesium alloy through severe plastic deformation and short annealing

“…Thus, deformation could be well described by the climb-controlled dislocation creep associated by lattice diffusion. The Q value obtained in this study was comparable to the strain rate test method reported by Somekawa, et al [169] at higher temperature from 573 to 623 K (128 kJ mol-1), and very close to the creep test result reported by Hyun and Kim [170] at temperature from 423 to 473 K at high stress level (123.9…”