*3.2. The E*ff*ect of Severe Plastic Deformation*

After reaching the homogenized (initial) state, the samples were HPT processed at a hydrostatic pressure of 4 GPa by 0.5 and 2 rotations, reaching torsional strains up to γ*T*~100. After that, microhardness (HV0.05) measurements were carried out while distributing them over the whole cross section. In particular, microhardness was measured along entire radii of the disc-shaped sample. In Figure 7, the microhardness values are presented as a function of torsional shear strain γ*<sup>T</sup>* calculated according to Equation (1). After HPT of the furnace-cooled samples, the microhardness can be said to increase with increasing γ*T*, and finally reaches saturation at around HV0.05 = 160 for all four alloys, while for Mg0.3Ca the saturation is reached already at around HV0.05 = 72 (Figure 7).

**Figure 7.** *Cont.*

**Figure 7.** Microhardness results for (**a**) Mg5Zn0.3Ca, (**b**) Mg5Zn, (**c**) Mg5Zn0.15Ca, (**d**) Mg5Zn0.15Ca0.15Zr and (**e**) Mg0.3Ca in the initial state (IS–dotted line) after furnace-cooling (FC, black) and quenching (Q, red) and additional HPT deformation at room temperature at 4 GPa, 0.5 and 2 rotations giving torsional strains up to γ*T*~100.

However, starting with the quenched IS condition, which showed a higher microhardness than the furnace-cooled initial state, microhardness after HPT processing saturated at lower values, for Mg5Zn0.3Ca and Mg5Zn at around HV0.05 = 140 and for Mg5Zn0.15Ca and Mg5Zn0.15Ca0.15Zr at around HV0.05 = 150 for the highest γ*T*. For Mg0.3Ca, the saturation hardness was around HV0.05 = 64 only. The microhardness of the alloy with 0.15% Zr showed a slight tendency to decrease at higher strains (30-100) after a peak value at lower strains of approximately γ*<sup>T</sup>* = 20. In terms of relative effects after HPT processing, the samples in the IS (furnace-cooled) showed microhardness increases of 175% for Mg5Zn0.3Ca, 190% for Mg5Zn, 135% for Mg5Zn0.15Ca0.15Zr, 85% for Mg5Zn0.15Ca and 53% for Mg0.3Ca. Even in relative numbers, the HPT-processed IS (quenched) samples showed smaller increases, 100% for Mg5Zn0.3Ca, 87% for Mg5Zn, 77% for Mg5Zn0.15Ca, 113% for Mg5Zn0.15Ca0.15Zr and 19% for Mg0.3Ca.
