Rate sensitivity and tension–compression asymmetry in AZ31B magnesium alloy sheet

Abstract

The constitutive response of a commercial magnesium alloy rolled sheet (AZ31B-O) is studied based on room temperature tensile and compressive tests at strain rates ranging from 10 −3 to 10 3 s −1 . Because of its strong basal texture, this alloy exhibits a significant tension–compression asymmetry (strength differential) that is manifest further in terms of rather different strain rate sensitivity under tensile versus compressive loading. Under tensile loading, this alloy exhibits conventional positive strain rate sensitivity. Under compressive loading, the flow stress is initially rate insensitive until twinning is exhausted after which slip processes are activated, and conventional rate sensitivity is recovered. The material exhibits rather mild in-plane anisotropy in terms of strength, but strong transverse anisotropy ( r -value), and a high degree of variation in the measured r -values along the different sheet orientations which is indicative of a higher degree of anisotropy than that observed based solely upon the variation in stresses. This rather complex behaviour is attributed to the strong basal texture, and the different deformation mechanisms being activated as the orientation and sign of applied loading are varied. A new constitutive equation is proposed to model the measured compressive behaviour that captures the rate sensitivity of the sigmoidal stress–strain response. The measured tensile stress–strain response is fit to the Zerilli–Armstrong hcp material model.

Elevated temperature constitutive behavior and simulation of warm forming of AZ31B

“…To validate this assumption further some experiments using adhesively bonded stacked sheet samples, as described by Ghaffari , were performed. The stress-strain response of the stacked sheet samples matches that of the 6 mm thick monolithic samples within the low plastic strain range before de-bonding of the layers initiates (Kurukuri et al, 2014). As a result, the 6 mm samples were utilized in the current work to characterize the compressive response since a high level of plastic strain could be reached before specimen failure (usually by shear localization).…”

Dislocation Mechanics of High-Rate Deformations

“…Even more recently, the twin-effected polycrystal deformation behavior occurring in compression has been compared with absent twinning in tension for AZ31b and ZEK100 alloy sheet materials, including texture-based anisotropy measurements and use of Z-A description for the ratedependent tensile stress-strain behavior. [27,28] D. TASRA Applications for a-Iron, Copper, Tantalum, and a-Titanium Johnson and Cook (J-C) had provided their experimental test results to Zerilli and Armstrong for comparison with development of the physically based Z-A constitutive relations. [15,21] Figure 6 shows a comparison of the J-C longitudinal deformation shape of an Armco iron specimen and the Z-A physically based bcc model description employing Eqs.…”

A variational constitutive model for slip-twinning interactions in hcp metals: Application to single- and polycrystalline magnesium

“…for the transportation industry or for defense applications. However, its hexagonal crystal structure furnishes Mg and its alloys with a non-trivial mechanical performance which involves a substantial tension-compression asymmetry (Ball and Prangnell, 1994;Avedesian and Baker, 1999;Lou et al, 2007;Kurukuri et al, 2014) and a comparably low ductility at low holonomous temperature (Hauser et al, 1956;Tegart, 1964), as well as a pronounced deformation anisotropy, see e.g. the recent studies of Agnew and Duygulu (2005); Lou et al (2007); Stanford et al (2011).…”