Fig. 1 Representative microstructure of the rolled pure Mg sheets with different grain size (GS): a1-c1 IPF maps along ND; a2-c2 GS distributions. The IPF map and its corresponding GS distribution for each sample are in the same column. Note that the observation plane was always the plane containing RD and TD

Fig. 2 PFs for samples with GSs of a1-a4 10 μm and b1-b4 85 μm, with the average Schmid factor distribution for basal (Bas) < a > slip (the second column), prismatic (Pris) < a > slip (the third column), and pyramidal (Pyr) II < c + a > slip (the fourth column), respectively. The average Schmid factor (m) of individual slip modes for all the studied grains is provided at the top of each corresponding PF. This figure shows that the texture effect on the slip activations for different GSs was limited, and GS was the main variable in this work

Fig. 3 True stress-true plastic strain curves of the pure Mg sheets under RD tension

Fig. 4 Yield strength plotted as a function of the inverse square root of the mean GS (${d}^{-1/2}$), showing the Hall-Petch relationship, which was divided into two regions

Fig. 5 Representative SE SEM images illustrating microstructural evolution during tension for the samples with GS of a1-c1 10 μm; a2-c2 30 μm; a3-c3 85 μm. Slip trace and twin are indicated by the white and red arrows, respectively. The plastic strain levels are provided on the right-hand side. The same column represents the same plastic strain level, which is before loading, 2%, and 5%, respectively

Fig. 6 Frequency (and number) of grains exhibiting slip trace as a function of GS

Fig. 7 Schematic diagram of slip trace analysis, taking grain #80 at 2% strain as an example: a SE SEM image, b IPF map, c the theoretical slip traces with a table showing the m value for each slip system along RD loading. The theoretical slip plane traces and the unit cell orientation for the grain provided in c were calculated using the Euler angles acquired before loading

Fig. 8 Frequencies of individual slip modes at 5% plastic strain for samples with different GS. A total of 136 sets of slip traces were identified from 1150 grains

Fig. 9 Microstructure of the pure Mg sheet with different GSs at 5% strain: a1-a3 IPF maps and b1-b3 corresponding twin boundary maps. Black lines represent high angle GBs (GB misorientation angle > 10°), while red lines represent the boundary of tensile twins (TTWs)

Fig. 10 Fraction of twin area and twinned grains to total grains as functions of GS

Fig. 11 Hall-Petch relationships for a prismatic < a > slip and b pyramidal II < c + a > slip for the present Mg (hollow pentagram-shaped points and solid lines). The available Hall-Petch relationships of other materials (solid points and dashed lines) summarized from literature [9,15,42,43] are also provided for comparison