PSI - Issue 23

Jaroslav Čapek et al. / Procedia Structural Integrity 23 (2019) 3 –8 Jaroslav Čapek et al. / Structural Integrity Procedia 00 (2019) 000 – 000

7

5

Fig. 2: Microstructure of the annealed alloys (LM). a) ZnMg0.8Ca0.2 annealed for 4 h, b) ZnMg0.8Sr0.2 annealed for 4 h, c) ZnMg0.8Ca0.2 annealed for 24 h and d) ZnMg0.8Sr0.2 annealed for 24 h.

3.4. Mechanical properties

The differences in phase composition (MgZn 2 vs. Mg 2 Zn 11 ) which were observed across the sections of the ingots did not play any significant role on the studied mechanical properties of the materials. In the as-cast state, both alloys possessed approximately the same compressive yield strength (CYS) (see Table 2), while a higher microhardness was observed in the case of the as-cast ZnMg0.8Sr0.2 alloy. This was probably caused by the fine SrZn 13 particles dispersed in the Zn-Mg x Zn y eutectic mixture. Such fine particles had a hardening effect on the eutectic mixture and on the whole material as a consequence. The microhardness of both alloys increased after annealing to the same value of approximately 100 HV 1 units. This increase was caused by the transformation of the eutectic mixture in a massive intermetallic network (see Figs. 1 and 2). The microhardness was practically independent on the annealing time in the investigated time interval (4 – 24 h). Therefore, the HV 1 values measured after annealing for times between 4 and 24 h are not listed in Table 2. Annealing also played a role on the compressive properties. The CYS of both alloys increased after annealing, however, this increase was more significant in the case of the Ca containing alloy (see Table 2). The higher strengthening of the Ca-containing alloy may be ascribed to the coarse particles of the CaZn 13 phase.

4. Conclusion

In this study, the influence of the third alloying element (Ca or Sr) on the microstructural and mechanical characteristics of the ZnMg0.8Ca/Sr0.2 alloys was studied too. The microstructures of the alloys differed only in the