Activation Of Deformation Modes Research Articles

A comprehensive study on the mechanical behavior, deformation mechanism and texture evolution of Mg alloys with multi texture components

In this study, the deformation behaviors of Mg-3Al-1Zn alloy with multi texture components have been investigated using a combined experimental measurement and crystal plasticity modeling. Six types of multi textured samples were successfully prepared by an easily operated processing containing cold rolling, compression loadings, and subsequent annealing. The corresponding processing parameters to control multi texture components were also proposed. The effect of multi texture distribution on macroscopic mechanical response, activation of deformation modes, texture evolution, as well as the 101̅2 and 101̅1 twin fractions were systematically investigated. It’s a challenge work to model several texture components and random textures using EVPSC-TDT model for the first time. The simulation results generally match well with the experimental data. It has been found that the mechanical performance are strongly dependent on the multi texture components distribution and it was revealed by detailing the quantitative contribution of different deformation mechanisms to the plastic deformation. It’s the more disperse (0002) distribution of hard orientations that matters in enhancing the yield strength and ductility of samples with a given fraction of soft orientations. The findings in the present study are crucial for enriching the texture engineering for Mg alloys and could assist in designing better materials in term of mechanical properties and material performance.

Anisotropic cyclic deformation behavior of an extruded Mg-3Y alloy sheet with rare earth texture

Mg-RE (magnesium-rare earth) alloys exhibit pronounced in-plane anisotropy of mechanical response under quasi-static monotonic loading resulting from the RE texture, as extensively reported. In this work, an obvious in-plane anisotropy of cyclic deformation behavior was observed in an extruded Mg-3Y alloy sheet during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature. The extrusion direction (ED) samples displayed better fatigue resistance with almost symmetrical hysteresis loops and longer fatigue life compared with the transverse direction (TD) samples. The influences of texture on the deformation modes, cracking modes, and mechanical behavior of Mg-Y alloy sheets under cyclic loading were studied quantitatively and statistically. The activation of various slip/twinning-detwinning systems was measured at desired fatigue stages via EBSD observations together with in-grain misorientation axes (IGMA) analysis. The results indicate that the activation of deformation modes in the TD sample was featured by the cyclic transition, i.e., prismatic slip (at the tensile interval) →{10–12}tension twinning (at the compressive reversal) → detwinning + prismatic slip (at the re-tensile reversal). In the case of the ED sample, the cyclic deformation was dominated by the basal slip throughout the fatigue life. For cracking modes, intergranular cracking and persistent slip bands (PSB) cracking were the primary cracking modes in the ED sample while the TD sample showed a high tendency of {10–12} tension twinning cracking (TTW cracking). The underlying mechanisms influencing the activation of various slip/twinning-detwinning systems, as well as cracking modes and cyclic mechanical behavior, were discussed.

The deformation modes and transferability during low-cycle fatigue of Mg and Mg–3Y alloy

Mg–Y alloys show distinctly different slip/twinning activity under quasi-static monotonic loading at room temperature compared with pure Mg, as extensively reported. In this work, the influences of 3% Y addition on the deformation modes and transferability during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature of Mg sheets were studied quantitatively and statistically. The activity of various slip systems and twinning-detwinning were measured at desired fatigue stages via quasi-in-situ EBSD observations together with slip trace analysis. The results indicate that the activation of deformation modes in pure Mg was featured by the cyclic transition, i.e., tension twinning (at the compressive reversal) → detwinning + basal slip (at the tensile reversal). In Mg–3Y alloy, basal slip dominated the cyclic deformation throughout the fatigue life span. Compared with pure Mg, Mg–3Y alloy displayed the enhanced activity of various slip systems, including basal, prismatic, and pyramidal slip systems, but lower twinning-detwinning activity. For deformation transferability, mk, which is the product of the Schmid factor (SF) and the geometric compatibility factor (m’) values of the adjacent grains, was used to evaluate the slip transferability and twinning transferability at grain boundaries. Mg–3Y alloy showed a higher likelihood of slip transfer but lower twinning transferability than pure Mg. The underlying mechanisms affecting the activity of various slip systems and twinning, as well as deformation transferability and mechanical behavior, were discussed.

Effect of shear deformation on plasticity, recrystallization mechanism and texture evolution of Mg–3Al–1Zn alloy sheet: Experiment and coupled finite element-VPSC simulation

Microstructure characterization and texture evolution of multi-passes isothermal symmetry and asymmetry rolling, or namely differential speed rolling (DSR), of Mg–3Al–1Zn alloy sheets were systematically investigated at different temperatures and strain levels. Also, two scale model coupling finite element and a visco-plastic self-consistent model (FE-VPSC) was employed. Results indicate that the predominant dynamic recrystallization (DRX) mechanism transits from twinning DRX at 150 °C to continuous DRX at 250 °C attributed to the distinctively activated deformation modes. It was found that shear deformation induced in DSR plays a crucial role on the activation of deformation modes and related DRX mechanisms. Based on the calculation of effective Schmid factor (ESF), shear deformation is believed to promote the activation of contraction twinning and pyramidal <c+a> slip by increasing their ESFs. Furthermore, the concentration of grain orientations caused by profuse operation of basal <a> slip can facilitate the activation of twinning and pyramidal <c+a> slip during DSR. As a result, twinning DRX dominated region was obviously enlarged owing to a larger fraction of twinning at low temperature (<200 °C). Meanwhile, profuse activation of pyramidal <c+a> slip at high temperature (>200 °C) can accelerate the continuous DRX. After annealing at 250 °C for 1 h, fine grains with an average size of 3.36 μm and a large basal titled angle (∼26°) were attained for the twinning DRX controlled sheet at 150 °C.

Orientation Evolution in the {0001}-Oriented Hexagonal Crystal during Channel Die Compression

The activity of deformation modes and orientation evolution in the {0001}- oriented hexagonal crystals with basal slip as easy slip mode during channel die compression were investigated by crystal plasticity finite element method (CPFEM). Material parameters of magnesium and its alloys were used in CPFEM simulation. The pyramidal &lt;c+a&gt; slip contributes most of the strain in all cases of relative CRSS value and friction coefficient between mold and material. The friction coefficient has a more significant influence on the activity of various deformation modes and the orientation deviation from ideal {0001} orientation (&lt;0001&gt;//ND) compared with the relative CRSS value. The deviation angle can reach about 20° after 70% applied reduction under the friction coefficient of 0.20.