*3.4. Total Hardness Increase after Processing*

The total hardness increase along the processing history of Mg5Zn0.3Ca and Mg5Zn in the IS (quenched and furnace-cooled) is summarized in Figure 11. A percentage in a bar shows the hardness increase from one processing stage to the next one. A percentage above a bar shows the total hardness increase from the first processing stage to the last one. A very high total hardness increase of up to 200% for Mg5Zn could be reached for the furnace-cooled samples, while the quenched ones showed a total hardness increase of only 100%.

The maximum hardness increase for furnace-cooled samples of about 200% could only be reached for Mg5Zn and Mg5Zn0.3Ca. Mg0.3Ca (Figure 12) showed a surprisingly high hardness increase of 150%, whereas Mg5Zn0.15Ca and Mg5Zn0.15Ca0.15Zr showed only an increase of 100%. The last two alloys did not show a reaction to heat treatments at all.

**Figure 11.** Total microhardness increases of Mg5Zn0.3Ca and Mg5Zn in the IS (furnace-cooled and quenched) and additional HPT deformations after 4 GPa and 0.5 rotations and additional heat treatment at 100 ◦C for 24 h.

**Figure 12.** Total hardness increases of Mg5Zn0.3Ca, Mg5Zn, Mg0.3Ca, Mg5Zn0.15Ca and Mg5Zn0.15Ca0.15Zr from the IS (furnace-cooled), HPT processing at 4 GPa and 0.5 rotations; and additionally, heat treatment at the peak temperatures of 100 ◦C for 24 h, and 75 ◦C for 24 h for Mg0.3Ca.
