**5. Conclusions**

Melting of MZ + 0.0Sn starts at 344 ◦C, while with the addition of 0.5–3.0 wt.% of Sn, melting starts already at 334 ◦C. Melting is finished at 382 ◦C for the MZ + 0.0Sn and this temperature is being continuously decreased to 376 ◦C by the addition of up to 3 wt.% of Sn.

Main phases identified in the MZ + 0.0Sn alloy were η(Zn) and α(Al) solid solutions as well as Mg2Zn11 and MgZn2 intermetallic phases. Addition of Sn enabled the formation of Mg2Sn intermetallic phase at the expense of MgxZny phases, while mainly affecting the vol.% of Mg2Zn11.

The microstructure is dendritic for all as-cast alloys. The interdendritic areas are formed by the binary, ternary and quaternary eutectics specific for each alloy. Alloying with Sn causes the following changes of microstructural components: ternary eutectics consisting of η(Zn), α(Al) and MgxZny phases are gradually replaced by quaternary η(Zn), α(Al), MgxZny and Mg2Sn eutectics. Binary η(Zn) + MgxZny eutectics are gradually replaced by binary η(Zn) + Mg2Sn eutectics.

For the MZ + 0.0Sn and MZ + 0.5Sn alloys, the original dendritic character of the microstructure can still be recognized even after annealing. At the same time, the individual phases from the eutectics are connected to discrete particles, and thus the original eutectics are not recognizable anymore. Introducing 1 to 3 wt.% of Sn into this alloy system enabled a more effective spheroidization and agglomeration of individual phase particles significantly changing even the shape of the primary η(Zn) dendrites.

Annealing causes slight changes in the phase composition. For MZ + 0.0Sn mainly MgZn2 is transformed to Mg2Zn11. For the alloys with Sn, the volume content of Mg2Zn11 is partially increased mainly at the expense of Mg2Sn.

The microhardness is decreasing with the increasing of Sn content. The annealing changes the microhardness only slightly.

Based on microstructure observation, these alloys are overall suitable for coatings exposed to extended high temperature exposure. As coatings of steel substrates, their corrosion properties will be at least maintained as reported in part two of this research: The effect of Sn addition on Zn-Al-Mg alloy-Part II.

**Author Contributions:** Conceptualization, P.G. and M.K.; methodology, P.G., Z.G. and M.K.; validation, P.G., Z.G., M.K. and H.S.; formal analysis, P.G., Z.G.; investigation, P.G., Z.G., M.K. and H.S.; resources, P.G., Z.G. and H.S.; data curation, P.G., Z.G. and M.K.; writing—original draft preparation, P.G. and Z.G.; writing—review and editing, P.G. and M.K.; visualization, P.G. and Z.G.; supervision, P.G. and Z.G.; project administration, P.G.; funding acquisition, M.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Grant Agency VEGA of the Slovak Ministry of Education, Research, Science and Sport, Project No. 1/0490/18: "The effect of microstructure and phase composition on corrosion resistance of hot dip alloys" and by the Slovak Research and Development Agency under the Contract no. APVV-20-0124.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data sharing is not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

