Strain rate sensitivities of deformation mechanisms in magnesium alloys

Abstract

Strain rate sensitivity (SRS) is an important material property that governs the rate dependent mechanical behaviors associated with deformation rate changes, creep, stress relaxation, formability, etc. The variety of activated deformation mechanisms of magnesium alloys under different loading paths, e.g. tension vs. compression, implies that SRS of magnesium alloys obviously depends on loading paths, and each deformation mechanism has its own SRSs. However, a single SRS scheme is commonly employed in numerical modeling to describe the rate dependent behaviors of magnesium alloys, which disregards the distinction of SRSs among different deformation mechanisms. The implementation of the constitutive model that works for a wide range of values of SRSs has been a challenge to crystal plasticity modeling for metals with multiple deformation mechanisms like magnesium. Especially, very small values of SRS, corresponding to low rate-sensitivity, generally lead to high nonlinearity involved in the governing equations, and then computational failure. In this paper, the elasto-viscoplastic selfconsistent (EVPSC) crystal plasticity model is improved to enhance its numerical robustness for very small SRS values. Taking advantage of this improvement, different SRSs for various deformation mechanisms are employed to investigate the strain rate dependent behaviors of magnesium alloys at room temperature. First, the SRSs for various deformation mechanisms are determined based on the compressive stress relaxation tests on an AZ31 alloy plate; secondly, the obtained SRSs are applied to interpret internal elastic strain evolution of the same magnesium alloy under in-plane compression; finally, the determined SRSs are applied to investigate the deformation of another AZ31 alloy under various deformation paths and strain rates. The present work is the first effort on studying effects of strain rate-sensitivity on mechanical behavior of Mg alloys under wide range of applied strain rates by using an improved self-consistent polycrystal plasticity model. Good agreement between the experiments and simulations reveals the importance and necessity of using different SRSs for the deformation mechanisms involved. The rate dependent behaviors of magnesium alloys can be better described by using multiple SRSs associated to each operative deformation mechanism.

High-throughput screening of strength and creep properties in Mg-Zn alloys

“…trenching on either side of the ROI to get a triangular wedge; (c) lift-out of the specimen using a nanomanipulator; (d) attachment of a specimen wedge on the microtip post; (e) one specimen wedge on the microtip post at the beginning of annular milling; (f) final needle specimen with <100 nm end diameter [97]. (1) the standard load transducer (2) high load transduce (3), optical camera and (4) [42,46]; (c) to determine the activation volume V*; (d) The activation volume V* as a function of Zn content from current work and in [44]. [132,133].…”

Localized deform behavior of AZ31B magnesium alloy by numerical simulation

“…With the development of computational material, more and more constitutive models were proposed to improve the calculated precision of magnesium alloys deformation behaviors [17][18][19]. The treating multiple/small strain rate sensitivities was benefited for elasto-viscoplastic self-consistent crystal plasticity model, which was successfully applied to investigate the deformation of AZ31 magnesium alloy under various deformation paths and strain rates [17].In order to describe the dynamic stress-strain response of the AZ31B alloy, a new dynamic constitutive model was scientifically established.…”

“…The treating multiple/small strain rate sensitivities was benefited for elasto-viscoplastic self-consistent crystal plasticity model, which was successfully applied to investigate the deformation of AZ31 magnesium alloy under various deformation paths and strain rates [17].In order to describe the dynamic stress-strain response of the AZ31B alloy, a new dynamic constitutive model was scientifically established. The constitutive model was based on crystal plasticity and the approach of strain-rate sensitivity control used in the Preston-Tonks-Wallace model [18]. In fact, Johnson-cook constitutive model was widely used in high strain rate deformation behavior of metal.…”

Investigation of the In-Plane Mechanical Anisotropy of Magnesium Alloy AZ31B-O by VPSC–TDT Crystal Plasticity Model

“…In fact, an appropriate crystal plasticity model for describing both twinning and detwinning had not been developed until the work of Wang et al [37]. The predictive capability of the twinning and detwinning model (TDT) has been demonstrated by applying it to magnesium alloys under both monotonic and cyclic loadings [38,39,40,41,42,43], where twinning and/or detwinning were best exhibited.…”