*3.5. Tensile Strength and Ductility*

Tensile tests were conducted for all five alloys in the initial state; HPT-deformed (0.5 and 2 rotations); and additionally, heat treated for 24 h at 100 ◦C. Representative engineering stress–strain curves obtained by micro-tensile testing are shown in Figure 13. In cases wherein no relative maximum was seen, the ultimate tensile strength (UTS) was derived by determining the maximum load and the initial cross section of the sample. For the determination of yield strength, a constant plastic strain of 1% was chosen. The difference in yield strength and UTS of the IS and HPT-processed samples typically amount to 100 MPa and 200 MPa, respectively. HPT-processing more than doubles the yield strength and also drastically increases the ultimate tensile strength by ~140% for Mg0.3Ca. For Mg5Zn0.3Ca and Mg5Zn, the UTS increased by ~45% and ~75%, respectively. For Mg5Zn0.15Ca and Mg5Zn0.15Ca0.15Zr, HPT processing reduced the maximum elongation to ~5%. This means that the ductility is much lower than that of the material in the initial state. The post-HPT heat treatment (condition of peak hardness) led to a further strong increase in yield strength by up to ~85% and a slight decrease in ultimate tensile strength. However, the elongation to failure still reached 5% only,

not showing any response to thermal treatment after HPT-processing. The average values of strength and ductility measured in the tensile tests are summarized in Table 4.

**Figure 13.** Representative tensile stress–strain curves of IS, IS and heat-treated, HPT-processed (0.5 and 2 rotations) and HPT-processed and subsequently heat-treated Mg5Zn samples. Both heat treatments were done at 100 ◦C through 24 h.


