Strain rate dependence of twinning at 450 °C and its effect on microstructure of an extruded magnesium alloy

Origin of the twinning to slip transition with grain size refinement, with decreasing strain rate and with increasing temperature in magnesium

“…The rationale behind these observations is that the CRSS for twinning is less sensitive to strain rate and temperature than that of slip [5] and this is reportedly consistent with the large core width (w) predicted for {1 0 1 2} zonal twinning dislocations (w = 6a) [1]. Indeed, the CRSS of tensile twinning has been shown to remain basically constant at strain rates ranging from 10 À4 to 10 3 s À1 and at temperatures comprised between room temperature and 300°C [3,6,7,27,[34][35][36]. It is generally believed that, with increasing temperature, twinning is gradually replaced by non-basal slip, as it is known that the CRSSs of prismatic and pyramidal systems decrease rapidly with temperature [3,36].…”

“…Testing conditions such as strain rate and temperature are also known to alter dramatically the twinning activity [1,5,7,[25][26][27][28][29][30][31][32][33][34][35]. In particular, decreasing the strain rate and/ or increasing the deformation temperature hinder twin activation to such an extent that, at a constant strain rate, twinning might be suppressed at sufficiently low temperatures and conversely, at a constant temperature, twin activation ceases below a critical strain rate [34].…”

“…In particular, decreasing the strain rate and/ or increasing the deformation temperature hinder twin activation to such an extent that, at a constant strain rate, twinning might be suppressed at sufficiently low temperatures and conversely, at a constant temperature, twin activation ceases below a critical strain rate [34]. The rationale behind these observations is that the CRSS for twinning is less sensitive to strain rate and temperature than that of slip [5] and this is reportedly consistent with the large core width (w) predicted for {1 0 1 2} zonal twinning dislocations (w = 6a) [1].…”

Structure and Properties of Hot-Rolled and Annealed Az61 Magnesium Alloy

“…Valle et al processed AZ61 by hot rolling in several thermomechanical routes at strain rates ranging from 10 −4 to 10 −2 s −1 and observed that a decrease of basal texture intensity together with dynamic recrystallization (DRX) led to the enhancement of AZ61 ductility manifested a capacity for large deformations in one pass [6]. Ma et al processed magnesium alloy AM30 at high strain rates and found that, at strain rates > 0.8 s −1 , profuse twinning is activated [7]. On the one hand, twinning has an impact on hardness, but on the other, the twins may accelerate the DRX processes, enhancing the ductility of the material [7].…”

“…Ma et al processed magnesium alloy AM30 at high strain rates and found that, at strain rates > 0.8 s −1 , profuse twinning is activated [7]. On the one hand, twinning has an impact on hardness, but on the other, the twins may accelerate the DRX processes, enhancing the ductility of the material [7]. Zhang et al processed magnesium alloy AZ31B in a repeated unidirectional bending process (RUB) followed by annealing [8].…”