Extension twin variant selection during uniaxial compression of a magnesium alloy

Abstract

Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific {10-12} extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor. TITLE PAGE Abstract:Samples of the magnesium alloy AZ31 have been deformed by compression to strains of 5% and 10% and microstructural observations made to investigate the activation of specific {1012} extension twin variants. The twinning has been analyzed on a grain-by-grain basis for more than 260 grains to determine both the number of extension twin variants in each grain, and the volume fraction of each. At 5% strain approx. 30% of the grains contain twins corresponding to variants with the third or lower ranked Schmid factor, with the fraction increasing to 40% after 10% compression. A grain size effect is also observed in that smaller grains are less likely to contain lower ranked twin variants. For both 5% and 10% compression no clear relationship exists between the volume fraction of each twin variant in a given grain population and the Schmid factor for the twin variant. A positive linear relationship can be defined, however, between the maximum twinning fraction that a twin variant can reach and its Schmid factor.

Twin nucleation and variant selection in Mg alloys: An integrated crystal plasticity modelling and experimental approach

“…There are six variants of extension twins (variants of {101 ̅ 2} 〈101 ̅ 1〉) as shown in Table 1, therefore the next step is the identification of variant type of the twins in grains A-D. There are several methods to identify the twin variants such as by trace and orientation analysis [Jiang et al (2008), Pei et al (2012)]. In the current study the method of orientations is employed, where the crystallographic orientations of all six twin variants corresponding to parent grain orientation are calculated using the procedure outlined in [Niewczas (2010)].…”

Activation of multiple twins by pre-tension and compression to enhance the strength of Mg–3Al–1Zn alloy plates

“…4d), two twin variants from the same variant pair have the highest SF values. As reported in previous studies, the variant selection of primary {10-12} twins in compressed Mg alloys is mainly governed by the Schmid law [8,11,13,14]. Therefore, multiple twin variants are more likely activated in the basal textured Mg alloy with 〈10-10〉 concentrated toward RD.…”

Deformation Mechanisms in a Rolled Magnesium Alloy Under Tension Along the Rolling Direction

“…For example, in the current study, three twin variant pairs are V1 and V4, V2 and V5, V3 and V6, respectively. Among these twin variant pairs, three misorientation relationships can be obtained: 60 and 60.4° between different twin variant pairs and 7.4° between the same twin variant pairs (Jiang et al, 2008; Pei et al, 2012).…”