Abstract
This study was aimed at evaluating the microstructure, mechanical behavior and texture response of extruded AM30 magnesium alloy in uniaxial compression with special attention to the effect of compressive strain amount, sample orientation, loading direction, compressive prestrain, and annealing. Compressive deformation along the extrusion direction (ED) resulted in sigmoidal true stress-true strain behavior together with three distinct stages of strain hardening, due to the presence of two sets of basal textures {0001}<2110> and {0001}<1010>, with caxes aligned nearly parallel to the normal direction (ND) of the extruded plate which facilitated the occurrence of {1012} extension twinning. The effect of in-plane loading direction, i.e., 0°,15°, 30°, 45° from the ED on the compressive flow behavior was investigated, which revealed nearly constant yield and ultimate compressive strengths but with a remarkable increase of fracture strain compared to the ED sample. The effect of pre-strain along the ED on the formation of twinning and texture was investigated during re-compression along the ED, transverse direction (TD) and ND. In the two-step ED-ED compression, the disappearance of twin boundaries or the coalescence of twins via twin growth was observed. After pre-strain along the ED, re-compression along the TD showed two seemingly opposite phenomena, i.e., the formation of new twins and de-twinning to be coexistent due to the presence of multiple sets of textures after the first-step pre-straining. The de-twinning activity decreased and the texture weakening was achieved with increasing pre-strain in the ED while doing recompression along the ND at a constant strain amount. Texture measurements revealed that the c-axes of hcp unit cells were always rotated towards the compression direction, regardless of compression in the ED, TD or ND. The annealing temperature and time also had a pronounced effect on microstructure and texture evolution. With increasing annealing time, the twins in the pre-compressed samples were observed to disappear gradually, as demonstrated by a decreased volume fraction of twins and weakened texture which became more randomly distributed. As a result, during re-compression along the ED, fewer twin formation and less intense texture were observed, resulting in a significant increase of ductility.
Highlights
1.1 Introduction and MotivationDuring the early years of the twenty-first century, the efficiency of energy consumption has become increasingly important, and the demand for energy has increased tremendously, while at the same time oil’s “tipping point” has passed, based upon the report in a recent Nature article [1]
Active twin variants reflected from the highest Schmid factor value were significantly dependent on the activation mode which was governed by the combination of the crystallographic lattice orientation and the applied loading direction
The results suggest that the active twin variants reflected by the high Schmid factor value were significantly dependent on the activation mode which was governed by the combination of the crystallographic lattice orientation with the applied loading direction
Summary
During the early years of the twenty-first century, the efficiency of energy consumption has become increasingly important, and the demand for energy has increased tremendously, while at the same time oil’s “tipping point” has passed, based upon the report in a recent Nature article [1]. Recrystallization has been reported to be an effective technique in plastically deformed magnesium alloys to produce nucleation sites within twins and untwinned regions with modified grain size, shape or texture. This opens up the possibility of controlling the mechanical response by designing crystallographic textures appropriate to particular strain paths. The major objectives of the present research are to identify the role of deformation twinning (as one of the deformation mechanisms) on the plastic deformation behavior of extruded magnesium alloys, and its correlation with microstructure and textures, based on a fundamental understanding of the mechanical properties under various loading conditions and sample orientations using X-ray diffraction as a major characterization tool. The work constitutes a benchmark for understanding the effects of the plastic deformation mechanisms, such as twinning, de-twinning and dislocation slip on the mechanical behavior in wrought magnesium alloys
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