Reduction of compression-tension yield asymmetry in binary MgGd alloys via mastering their crystallographic textures

Abstract

Compression-tension asymmetry (CTA) in yield strength is one of the issues that hinders widespread application of wrought Magnesium (Mg) alloys. Strong basal texture formed in thermomechanical processing and the difference in activation of deformation twinning in tension and compression are responsible for CTA. To reduce CTA, the readily implementable Double Equal Channel Angular Pressing (D-ECAP) is used in this study for altering the microstructure and texture of Mg samples. Mg bars containing 1, 5, and 10 wt% Gd were subjected to D-ECAP at 400 °C. Due to plastic strain, the average grain sizes decreased from several hundred microns to about 13.4 μm, 5.6 μm, and 5.1 μm, respectively. All processed samples showed high strength and characteristics shear textures. The crystallographic textures displayed the so-called C1-C2 and B fibers. C1-C2 were the major fibers in the 1 % and 5 % Gd samples, while the B and C1 fibers appeared in the 10 % Gd sample. C1-C2 requires high activity of pyramidal <c + a > slip, and B belongs to basal slip. The CTA was measured by the ratio of the compression/tensile yield stress and significant increase in CTA was obtained on the D-ECAP processed samples with respect to the base alloys. The CTA reached 0.85 in the Mg10Gd alloy without sacrificing the yield strength. Polycrystal plasticity simulations were done using the experimental textures and good reproduction of the CTA values were achieved. The simulation results also revealed the relative activity of the slip and twinning systems for understanding the mechanisms that control the CTA. The results of this study revealed that D-ECAP is an efficient processing technology that can be widely used in the preparation of high-performance MgGd alloys.