Characteristics of different 10-12 twin variants in magnesium alloy during room temperature dynamic plastic deformation
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Recently, the {10-12} twin variants activated during dynamic plastic deformation (DPD) of Mg alloy have been investigated by analyzing their Schmid factors (SFs), and their contributions to deformation have been calculated. During DPD of Mg–3%Al–1%Zn alloy, different {10-12} variants are generated relative to their SFs when initial grains have defined orientations with one a-axis of the crystal lattice at roughly 0 or 30° from the compression direction. The volume fraction of twins deeply influences the strain accommodated by twinning. The {10-12} variant pair with the maximum SF accommodated about 90% of the twinning strain. Its high volume fraction indicated that both nucleation and growth mechanisms played important roles in the strain accommodation. Other {10-12} variants had a lower volume fraction and accommodated twinning strain mainly by twin nucleation and made a lesser contribution to the total deformation. I. INTRODUCTION
Deformation twinning plays an important role in plastic deformation of hexagonal close-packed (hcp) metals because of their limited slip systems.1–3 For pure Mg and Mg alloys that have relatively low stacking fault energies, deformation at low temperatures and/or at high strain rates leads to easier-twinning nucleation as dislocation activity is suppressed.4–6 Although several types of twins have been found in Mg alloys, {10-12} twinning is considered to be more frequently activated.7–9 From previous investigations on pure Mg and Mg alloys,1–5,7–11 the {10-12} twins, including six equivalent variants, have been conventionally discussed as a group (i.e., extension twins). However, the characteristic of each {10-12} variant and the effect of different variants on plastic strain are still not very clear because the type of twin variants and twin morphologies are different with increasing levels of strain.4,10 To facilitate twinning, dynamic plastic deformation (DPD) was used to deform samples to various levels of strain in this study. The {10-12} twinning variants activated were investigated by calculating their Schmid factors (SFs), and their contributions to deformation were discussed by analyzing the deformation mechanisms.
III. EXPERIMENTAL RESULTS AND DISCUSSION A. Microstructure and texture evolution during deformation
II. EXPERIMENTAL METHOD
The material investigated was a commercially hot-rolled AZ31 Mg alloy plate (Mg–3%Al–1%Zn), which were annealed at 420 °C for 3 h and then furnace cooled, leading to a strong basal texture and a twin-free equiaxed grain a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.162 J. Mater. Res., Vol. 28, No. 14, Jul 28, 2013
http://journals.cambridge.org
structure with an average grain size of 34 lm as evaluated by the linear intercept method, as shown in Fig. 1(a). Cylinders (8 mm in diameter and 12 mm tall) were cut from this plate along the rolling direction (RD), i.e., the loading direction (LD) is parallel to the RD (Fig. 2). Samples were subjected to DPD just once with Instron Dynatup 8120 testing m
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