PSI - Issue 23

Jan Pinc et al. / Procedia Structural Integrity 23 (2019) 21–26 Jan Pinc et al./ Structural Integr ty P o edi 00 (2019) 000 – 000

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Fig. 2 Microstructure of the annealed ZnMg0.8Ca0.2 with red marked calcium phases.

2.2. Influence of cooling rate to the structure of material

Microstructures of the ingots with a diameter of 5 and 50 mm are shown in Fig. 3. It can be seen that the dendrite arm spacing increased with decreasing cooling rate. More precisely, the difference in the dendrite sizes between the extremes (5 mm and 50 mm) was approximately 15 µm (Table 1). It was found by XRD that the phase composition of the as-cast material was not the same on the edges and in the core of the 50 mm ingot. It is obvious that the reason of this inhomogeneous structure were the different cooling rates in the mentioned areas.

Table 1. Changing of dendrite size in dependence on cooling rate. Mold diameter Dendrite size 5 mm 6 µm 30 mm 11 µm 50 mm 20 µm

Fig. 3 Microstructure of samples with diameter a) 5 mm (higher cooling rate) and b) 50 mm (lower cooling rate).