Publication Abstract
Effect of Twinning, Slip, and Inclusions on the Fatigue Anisotropy of Extrusion-textured AZ61 Magnesium Alloy
Jordon, J. B., Gibson, J. B., Horstemeyer, M., El Kadiri, H., Baird, J., & Lou, A. A. (2011). Effect of Twinning, Slip, and Inclusions on the Fatigue Anisotropy of Extrusion-textured AZ61 Magnesium Alloy. Materials Science and Engineering A. Elsevier. 528, 6860-6871.
Abstract
In this study, experiments were conducted to quantify structure-property relations with respect to
fatigue of an extruded AZ61 magnesium alloy using a MultiStage Fatigue (MSF) model. Experiments were
conducted in the extruded and transverse directions under low and high cycle strain control fatigue conditions.
The cyclic behavior of this alloy displayed varying degrees of twinning and slip depending on
the strain amplitude as observed in the hysteresis loops of both directions. Under low cyclic conditions,
asymmetrical stress strain response was observed for both orientations. However, systematic stabilization
of the hysteresis occurred by half-life due to subsequent twinning and detwinning mechanisms.
In addition, under high cycle fatigue, pseudo-elasticity was observed at the first and at half-life cycles.
Structure-property relations were quantified by examining the fracture surfaces of the fatigued specimens
using a scanning electron microscope. In terms of crack incubation, fatigue cracks were found to
initiate from intermetallic particles (inclusions) that were typically larger than the mean size. Quantified
sources of fatigue crack incubation, microstructurally small cracks, and cyclic stress–strain behavior
were correlated to the MSF model. Based on the specific material parameters, the MSF model was able to
predict the difference in the strain-life results of the AZ61 magnesium alloy in the extruded and extruded
transverse directions including the scatter of the experimental results. Finally, the MSF model revealed
that the inclusion size was more important in determining the fatigue life than the anisotropic effects
from the texture, yield, and work hardening.