Statistical Study of Activity and Hall–Petch Coefficients for Individual Slip Modes in Basal-Textured Pure Mg

Abstract

This work investigated the effects of grain size (GS) on individual slip mode activities and the corresponding Hall–Petch coefficients in a rolled basal-textured pure Mg sheet under uniaxial tension using statistical slip trace analysis and electron backscatter diffraction. The studied regions covered a total of 1150 grains, in which 136 sets of slip traces were identified and analyzed in detail. The basal < a > slip always dominated the deformation, whose frequencies decreased (from 81.0% to 62.5%) with increasing GS (from 10 to 85 μm). The prismatic < a > slip activity increased from 10.8% (10 μm) to 27.5% (85 μm), while that for pyramidal II < c + a > slip was almost constant. Critical resolved shear stress (CRSS) ratios were estimated based on the identified slip activity statistics, and then the Hall–Petch coefficients (k) of individual slip modes were calculated. The k value for prismatic < a > slip (194 MPa·μm^1/2) was lower than that for pyramidal II < c + a > slip (309 MPa·μm^1/2), which implies that pyramidal II < c + a > slip was more GS sensitive. Twinning activity exhibited a positive correlation with GS, though it remained limited partly due to the unfavorable loading direction. The macroscopic Hall–Petch relationship was divided into two regions, i.e., the k value (753 MPa·μm^1/2) for the coarse-grain region (30–85 μm) was significantly larger than that (118 MPa·μm^1/2) of the fine-grain region (10–30 μm), which could be attributed to the transition of predominant deformation mechanisms from slip to slip combined twinning with increasing GS. This work provides detailed and quantitative experimental data of the GS effects on individual slip activities of Mg and provides new insights into the Hall–Petch relationship for individual slip modes.