Manipulating deformation mechanisms with Y alloying of Mg

The effect of Y concentration on the slip and twinning mechanisms in binary Mg-Y alloys are investigated using transmission electron microscopy, electron backscattered diffraction, and visco-plastic self-consistent polycrystal constitutive modeling. Four concentrations of Y are studied in hot-rolled and recrystallized sheet material. The materials were deformed in tension and compression in the rolling direction and compression in the normal direction in order to invoke distinct proportions of slip and twin mechanisms with each test. Within the single crystal hardening model used in polycrystal modeling, a slip-twin interaction law is introduced to account for dislocation density reductions due to dislocation absorption during twin boundary migration. We show that increasing Y concentration reduces the intensities of both the initial and deformation textures. During deformation, the plastic anisotropy in yield stress, the tension-compression asymmetry, and amount of {10 (1) over bar2 }((1) over bar 011) twinning is shown to decrease with increasing Y. For each alloy, the model identifies a single set of material parameters that successfully reproduced all measured stress-strain curves and achieved agreement with measured deformation textures and twin area fractions. Transcending texture effects, the model interpretation of the flow responses suggests that increased concentrations of Y increase the critical resolved shear stress for basal slip but have negligible effects on the other slip modes. The reduced plastic anisotropy with increases in Y is explained by a concomitant decrease in the prismatic-to-pyramidal slip critical resolved shear stress ratio. The model suggests that their nearly equivalent critical resolved shear stress values lead to the enhanced non-basal activity of Mg-Y alloys, which was confirmed by transmission electron microscopy. The calculations suggest that beyond any texture differences, this reduction in twinning can be attributed to a slightly increased resistance for {10 (1) over bar2 }((1) over bar 011) twin propagation, particularly in the binary with the highest Y content.

Automated summary

The study investigates the effect of Y concentration on slip and twinning mechanisms in binary Mg-Y alloys. Increasing Y concentration reduces the intensities of the initial and deformation textures, as well as plastic anisotropy, tension-compression asymmetry, and twinning. The model suggests that increased Y concentration increases the critical resolved shear stress for basal slip and reduces plastic anisotropy, leading to enhanced non-basal activity in Mg-Y alloys.