Pseudoelastic behaviour of cast magnesium AZ91 alloy under cyclic loading–unloading

Anelasticity in cast Mg-Gd alloys

“…The larger anelastic strain at smaller grain sizes is consistent with the idea proposed in [9,11] that small grain sizes offer more nucleation sites for favourably oriented twinning to occur due to the increased specific grain boundary area. At the same time, smaller twins are less likely to relax plastically, so their tendency to revert can be expected to be larger as well.…”

“…This behavior of the 0.4Gd alloys is consistent with the behavior of the Mg-Zn and Mg-Al alloys reported in [5,6,9,11,13]. By the same token, the lack of difference between tension and compression for the 1.5Gd alloys, and the reversion, i.e., larger anelastic strain in tension, for the…”

“…The larger anelastic strain in compression than in tension for the pure Mg and the dilute (0.4Gd) alloy is consistent with the notion that the behavior arises from a combination of the polar nature of twinning and the fact that the twin mode with the lowest activation stress is the 'tension" {1012} twin: in a random polycrystal, the fraction of grains having their c-axis favourably oriented for (tension) twinning is larger under a compressive stress than under a tensile stress [5,[9][10][11]15]. This behavior of the 0.4Gd alloys is consistent with the behavior of the Mg-Zn and Mg-Al alloys reported in [5,6,9,11,13].…”

“…These twins are not fully stable in the deformed state [4] and tend to partly revert, once the applied stress is removed [5] or reversed [6,7], leading to hysteresis loops during loading and unloading. This type of hysteresis loops have been reported in pure Mg and Mg-Al [5,6,[8][9][10], and Mg-Zn [11]. Similar loops have also been observed in Zr [12].…”

Fatigue Crack Propagation Behavior of Textured Polycrystalline Magnesium Alloys

“…On the other hand, basal planes are distributed parallel to the extrusion direction by extrusion. Depending on their texture, wrought magnesium alloys show unique deformation behavior such as mechanical anisotropy, [2][3][4] pseudoelasticity in compression and tension loading-unloading, [4][5][6][7][8] and asymmetricity of stress-strain hysteresis loops in strain controlled low-cycle fatigue tests [9][10][11][12][13][14] and even in load controlled high-cycle fatigue tests, 4,9) etc. The orientation dependence of fatigue crack propagation behavior of magnesium single crystals, [15][16][17] and the effect of grain size [18][19][20][21] and texture [22][23][24][25] on fatigue properties of polycrystalline magnesium alloys have been reported in previous works.…”