*2.1. Materials, Samples and Preparations*

Five alloys were investigated with compositions Mg5Zn0.3Ca, Mg5Zn0.15Ca, Mg5Zn0.15Ca0.15Zr, Mg5Zn and Mg0.3Ca. The emphasis of analyses was laid on the first three alloys; the last two alloys helped to understand the main findings in-depth. The alloys were cast at the LKR (Leichtmetall-Kompetenzzentrum Ranshofen, Ranshofen, Austria), a subsidiary of AIT (Austrian Institute of Technology, Wien, Austria). The chemical compositions of the alloys are shown in Table 1.


**Table 1.** Chemical compositions of the investigated alloys.

The specimens were homogenized in a resistance furnace in argon protective gas atmosphere in order to avoid strong oxidation, at 450 ◦C for 24 h for all alloys, except Mg5Zn which was heat treated at 350 ◦C for 12 h [34]. After that, the samples were either furnace-cooled or quenched to room temperature, and investigated separately.

### *2.2. HPT-Processing*

For HPT-processing, disc-shaped samples with a diameter of 10 mm and a thickness of 0.7 mm were prepared. The hydrostatic pressure applied during HPT was 4 GPa, and the rotation speed was 0.2 rot/min. The samples were torsion strained to shear strains

$$
\gamma\_T = \frac{2\pi Nr}{h} \tag{1}
$$

with the von Mises strains <sup>ε</sup> being by a factor <sup>√</sup>3 smaller [35]. *<sup>N</sup>* means the number of rotations, *r* the sample radius and *h* the thickness of the sample. HPT-processing was performed at room temperature (RT).
