Demonstration of alloying, thermal activation, and latent hardening effects on quasi-static and dynamic polycrystal plasticity of Mg alloy, WE43-T5, plate

Abstract

The mechanical response of rare earth containing Mg alloy, WE43, plates is found to be more isotropic, as compared to conventional alloys like AZ31, despite a moderately strong texture. In order to understand the grain-level deformation mechanisms which are responsible, the elastoplastic self-consistent (EPSC) polycrystal plasticity code, including the recently developed twinning-detwinning (TDT) model, is used to describe the homogeneous plastic flow of WE43-T5, plate at quasistatic and dynamic strain rates. Latent hardening of the slip modes is based on a recent discrete dislocation dynamics study in order to reduce the number of empirical fitting parameters without sacrificing model fidelity. The approach accounts for the presence of the initial texture and its evolution during deformation. The observed flow stress, strain, and strain hardening anisotropies and asymmetries are well-described. A single set of parameters was used to fit the entire set of results, at a given strain rate, thus enabling determination of strain rate sensitivities of individual deformation modes. Basal slip and extension twinning are rateinsensitive, within the strain rate regime examined, whereas the prismatic and <c+a> slip exhibit strain rate sensitivities of 0.008 and 0.005, respectively. Various strengthening mechanisms such as precipitation, grain refinement and solid solution hardening effects on each individual deformation modes are assessed. The softer modes, basal slip and extension twinning, are greatly strengthened in this alloy, as compared to the harder modes such as prismatic and <c+a> slip, which renders this material more isotropic, even at the grain-level, as compared to conventional Mg alloys.

Effect of precipitate shape and orientation on Orowan strengthening of non-basal slip modes in hexagonal crystals, application to magnesium alloys

“…= f 3%, the CRSS increments for 〈 + 〉 c a slip systems are larger than 200 MPa, and those for basal and prismatic slip systems are 144 MPa and 114 MPa respectively. Whereas these values indicate a high strength improvement solely due to Orowan hardening, a caveat is put forward that the effective volume fraction of the strengthening precipitates may be much lower than the global volume fraction measured experimentally [19]. On the other hand, the size limit of shear resistant precipitates is unclear for certain phases, so the values may exceed the strengthening capability of precipitate.…”

“…On one hand, this scheme takes into account the probability of a dislocation experiencing different obstacle variants and spacings. On the other hand, it may deviate from the real case where the effective inter-particle spacing may be much more ̅ } 1120 plate and spherical precipitates, as observed in Mg alloy, WE43-T5 [19]. The three precipitate morphologies are represented by marker shapes circle, square and no marker respectively.…”

“…The following is an example of how to employ the relationships contained within this paper. In Mg alloy, WE43-T5 plate (hot rolled and artificially aged), precipitate plates on both prismatic planes as well as globular precipitates are present [19]. In what follows, the resultant absolute CRSS increment of all slip systems are evaluated with a fixed precipitate volume, as a function of volume fraction.…”

Uniaxial stress-driven grain boundary migration in Hexagonal Close-packed (HCP) metals: Theory and MD simulations

“…In the experimental aspects of Mg and its alloys, we mention a few such as the anisotropy decreases at high temperatures 5 (Stanford et al, 2011), the transmutation mechanisms of dislocations related to rapid hardening (Oppedal et al, 2012), twinning activity (nucleation and propagation) and deformation limits by in-situ compression/tension experiments and high-resolution electron backscatter diffraction (HREBSD) techniques (Khosravani et al, 2013(Khosravani et al, , 2015, the deformation modes and anisotropic behaviors for Gadolinium-contained Mg M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT alloys under tension investigated by in-situ scanning electron microscopy (Wang et al, 2016). The complex 10 loading paths in Mg alloys are also discussed, e.g.…”

“…In the modeling aspect of Mg and its alloys, many mechanics models are proposed such as a selfconsistent model with a local thermoelasto-viscoplastic behavior based on translated field techniques 15 (Mareau and Berbenni, 2014), a stochastic crystal plasticity model combining a Monte Carlo method with a continuum dislocation dynamics model (Askari et al, 2015), a multi-level constitutive model considering a combination of elasticity, slip and deformation twinning, derived by a two level homogenization scheme (Ardeljan et al, 2016), a generalized distortional hardening continuum model by assuming each part of dissipation non-negative (Shi et al, 2015), the crystal plasticity model for investigating the underlying de-20 formation mechanism upon two-step loading, focusing especially on the effect of twinning and detwinning activities (Hama et al, 2016), and the elastoplastic self-consistent (EPSC) polycrystal plasticity model, including a recently developed twinning-detwinning model for rare earth element containing Mg alloys at quasi-static and dynamic strain rates (Bhattacharyya et al, 2016).…”