Twinning-Detwinning in Pre-Compressed and Thermally Treated ZX10 and ZN10 Alloys.

Daria Drozdenko,Jan Bohlen,Sangbong Yi,Klaudia Fekete,Patrik Dobroň

doi:10.3390/ma13245605

Abstract

The deformation behavior of extruded Mg alloys with a Ca or Nd addition (up to 0.5 wt.%) is addressed with respect to a specified thermo-mechanical treatment, realized by pre-compression and subsequent heat treatment at intermediate temperature. The twinning–detwinning process is discussed with respect to the initial texture and applied heat treatment. Isothermal aging leads to precipitation and segregation along twin boundaries and dislocations in the pre-compressed Mg alloys, and, thus, variation in the mobility of twin boundaries (TB) is observed in the investigated alloys. Despite individual scenarios of TB mobility in particular grains, in general, the same TB mobility modes are observed in the alloys independently on Ca or Nd alloying. The microstructure development, particularly the twin volume fraction and the mobility of tensile {10-12} twin boundaries, is tracked using scanning electron microscopy, including backscattered electron (BSE) imaging and electron backscatter diffraction (EBSD) mapping.

Highlights

Mechanical twinning plays a key role in the deformation behavior of Mg alloys
In the as-extruded and thermo-mechanically treated (TMT) states, the ZX10 alloy is characterized by higher onset of plastic flow compared to the ZN10 alloy
For samples in the TMT state, S-shaped curves are observed for both re-compression and reverse tensile loading, which indicates the twinning activity: twin growth and shrinkage, respectively

Summary

Introduction

Mechanical twinning plays a key role in the deformation behavior of Mg alloys. The reorientation of the original lattice and introducing twin boundaries (TB) give rise for the activation of other deformation mechanisms (dislocation glide, detwinning, re-twinning) [1,2]. Dislocation slip restrained in its activity in the originally oriented lattice can become operative in the re-oriented one. TB introduce nuclei for dislocations [2], which contribute to deformation along the axis necessary for plastic deformation and usually require high applied stresses. Twin lamellae subdivide grains, act as non-dislocation barriers and contribute to the hardening of the material. The polar nature of twinning together with a strong texture of extruded Mg alloys, formed during processing, results in a significant asymmetry of mechanical properties [3,4,5,6,7]

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