**7. Mechanical Properties of Mg-Zn-{Ce, Y} Alloys**

Alloying Mg-Zn with rare earth elements is promising in modifying magnesium texture. Among rare-earth element, many researchers reported that micro-alloying Mg-Zn with yttrium or cerium exhibited a comparable ductility and formability with commercial magnesium alloys. Tables 3 and 4 summarize the mechanical properties of the published alloys in Mg-Zn-Y [154–157] and Mg-Zn-Ce [48,71,81,85,156–158], respectively.


**Table 4.** Mechanical properties of Mg-Zn-Ce alloys.



**Table 4.** *Cont.*


**Table 4.** *Cont.*

The addition of yttrium to Mg-Zn alloys enhances the formation of magnesium solid solution in ternary systems due to high solid solubility of yttrium in magnesium. Meanwhile, precipitation of nano-scale ternary phases as a result enhances mechanical properties. It is worth noting that the ratio of Zn/Y and heat treatment conditions play a significant role in mechanical properties as can be seen in Table 3. Unlike yttrium, the micro-addition of cerium to Mg-Zn reduces magnesium solid solution and precipitates a binary Mg12Ce phase as well as ternary nano-scale phases. Maximum solid solubility of cerium in magnesium is 0.5 wt.% at 590 ◦C and Mg12Ce precipitate up to 32.4 wt.% Ce. The existence of cerium and zinc in magnesium resulted in weakening structure and therefore enhanced ductility of magnesium alloys. Meanwhile, the percentage of cerium magnesium alloys must be in small amounts to hinder precipitation of high intensity of Mg12Ce phase; besides, heat treatment conditions and weight fraction of cerium play a remarkable role in mechanical properties of Mg-Zn alloys as shown in Table 4.

#### **8. Conclusions**

To reduce oil consumption in the automobile industry, designers are interested in lightweight alternative materials. Among lightweight materials is magnesium, and products of Mg-Zn alloys used in the automobile industry include transmission housings, heads, and engine blocks. In the current work, thermodynamic modeling of yttrium-zinc and yttrium-cerium phase diagrams were critically assessed, and the most appropriate phase diagrams were presented. Crystallographic data and solid solubilities of ternary phases in Mg-Zn-Y and Mg-Zn-Ce systems were evaluated. Lack of experimental data on ternary Mg-Zn-Y required further experimental investigations. Based on the recent findings, liquidus projections of the Mg-Zn-Y and Mg-Zn-Ce ternary phase diagrams were given. Ternary intermetallic phases and ternary solid solution reported in the literature were confusing, and additional key experiments are needed to resolve the discrepancies on the existence and chemical compositions of these phases. Mechanical properties reported in the literature of the two ternary systems were summarized.

**Author Contributions:** Conceptualization, M.A. (Mohammad Aljarrah); methodology, M.A. (Mohammad Aljarrah), J.A. and M.A. (Mohammed Alhartomi).; software, M.A. (Mohammad Aljarrah); validation, M.A. (Mohammad Aljarrah), J.A. and M.A. (Mohammed Alhartomi); formal analysis, M.A. (Mohammad Aljarrah), J.A. and M.A. (Mohammed Alhartomi); investigation, M.A. (Mohammad Aljarrah); resources, M.A. (Mohammad Aljarrah), J.A. and M.A. (Mohammed Alhartomi); data curation, M.A. (Mohammad Aljarrah); writing—original draft preparation, M.A. (Mohammad Aljarrah), J.A. and M.A. (Mohammed Alhartomi); writing—review and editing, M.A. (Mohammad Aljarrah); visualization, J.A.; supervision, M.A. (Mohammad Aljarrah); project administration, M.A. (Mohammad Aljarrah). All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Not applicable.

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