Strain-hardening behavior and microstructure development in polycrystalline as-cast Mg-Zn-Y alloys with LPSO phase subjected to cyclic loading

Abstract

The strain-hardening behavior and microstructural development of polycrystalline as-cast Mg-Zn-Y alloys with various volume fractions of the long-period stacking ordered (LPSO) phase subjected to cyclic loading were experimentally evaluated. For all alloys, cyclic loading tests with a constant strain amplitude of 0.5% for up to 100 cycles showed asymmetric cyclic hardening behavior. That is, the absolute value of the compressive peak stress significantly increased during cyclic loading while the tensile peak stress slightly decreased. With increasing volume fraction of the LPSO phase, the stress amplitude significantly increased. Cyclic loading tests after compressive preloading up to 200 or 250 MPa resulted in a significant increase in the stress amplitude, while a number of kink bands developed during preloading. For the cyclic hardening behavior, the contribution of the increase in kinematic hardening was significant in the alloys with a higher volume fraction of the LPSO phase.Transmission electron microscopy observation of the cyclically deformed Mg 85 Zn 6 Y 9 alloy indicated the formation of a deformation-induced band, where the crystal structure was transformed from 18R-LPSO to hcp-Mg with the exclusion of solute elements.

Strain hardening of as-extruded Mg-xZn (x = 1, 2, 3 and 4 wt%) alloys

“…Original dislocation tangling would hinder further movement of other dislocations. Considering the effects of grain size and dislocations, a recent model indicates that [10][11][12][13][14]35] :…”

“…temperature, and strain rate [11][12][13][14] . Jahedi et al [12] reported that strain hardening was strongly related to twinning and texture.…”

Strain Hardening Behavior in Mg–Al Alloys at Room Temperature

“…It can be seen that decreasing grain size weakens the strain hardening ability by reducing dislocation density and twinning content. Many studies also reported similar results . However, dislocation annihilation weakened by increasing Al solute atoms and non‐basal slips are easier to activate with the decreasing intensity of basal texture.…”

“…For this reason, many researchers have studied the strain hardening behavior in magnesium alloys, while changing various parameters such as grain size, twinning, texture, temperature, strain rate, and second phase . Shiraishi and Mayama reported that strain hardening behavior had some correlations with second phase . Jahedi and McWilliams found strain hardening behavior to be strongly related to twinning and texture .…”

Influence of Volume Fraction of Long-Period Stacking Ordered Structure Phase on the Deformation Processes during Cyclic Deformation of Mg-Y-Zn Alloys

“…In contrast, a gradual increase in YS was found for the tensile side of the cycle in Mg 99.2 Zn 0.2 Y 0.6 alloy. In cast Mg-LPSO alloys, besides the influence of the composition, the effect of compressive pre-loading was studied [25]. Both the compressive pre-loading and the higher LPSO content increased the share of the kinematic hardening to cyclic hardening.…”