# In Vitro Corrosion Behavior of Zn3 Mg0.7Y Biodegradable Alloy in Simulated Body Fluid (SBF)
## 3 Results
### Chemical Composition Analysis and Microstructural Aspects  
The experimental alloy Zn3 Mg0.7Y was mechanically ground and polished, and chemical etching was performed in order to highlight the microstructure. The general aspects of the microstructure are given in Figure 1(a). In Figure 1(b), the microstructure of the Zn3 Mg0.7Y alloy is presented after chemical etching. Structurally, a few different formations can be observed, and their chemical composition is presented in Table 1. The nature of the compounds is basically the same as Zn and Zn compounds (Mg2 Zn11, Mg12 ZnY and YZn12), as described and analyzed in a previous work through energy dispersive spectroscopy and X-ray diffraction [25].  
In addition to reduced percentages of oxygen, which was removed from the results table, the main elements identified on the material were Zn, Mg and Y, as shown in Figure 1(c). Quantitative results of chemical composition are given in Table 1 (mass and atomic percentages). The average chemical composition (on a 1 mm\({}^{2}\) area, from five different determinations) was 3.03 wt% Mg and 0.7 wt% Y. In order to establish the most important components, we performed four determinations in the areas marked in Figure 1(a). The compound analyzed in point 1 is a typical YZn12 compound (formula Zn24Y2) [26]. For point 2, the matrix of the material was analyzed, which consists of a solid solution of \(\alpha\)-Zn with dissolved Mg. Point three and four also represent ZnY and ZnMgY compounds.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Chemical**} & \multicolumn{2}{c}{**Zn**} & \multicolumn{2}{c}{**Mg**} & \multicolumn{2}{c}{**Y**} \\ \cline{2-7}  & **wt\%** & **at\%** & **wt\%** & **at\%** & **wt\%** & **at\%** \\ \hline General (1 mm\({}^{2}\)) & 96.3 & 93.3 & 3.0 & 6.3 & 0.7 & 0.5 \\ Point 1 & 90.0 & 92.4 & - & - & 10.0 & 7.6 \\ Point 2 & 98.2 & 95.4 & 1.8 & 4.6 & - & - \\ Point 3 & 91.0 & 93.2 & & & 8.9 & 6.7 \\ Point 4 & 92.8 & 94.1 & 0.2 & 0.7 & 7 & 5.2 \\ EDS detector & & 2.35 & & 1.10 & & 1.83 \\ Abs error [\%] & & & & & & \\ \hline \end{tabular}  
* St. dev: Zn: \(\pm\)1, Mg: \(\pm\)0.1 and Y: \(\pm\)0.05.  
\end{table}
Table 1: Chemical composition determination of ZnMgY alloy.  
At the microscale, no structural defects, such as pores, cracks or voids, were identified after the material was re-melted five times. The experimental alloy was chemically homogeneous, without separations and agglomerations of undissolved elements.  
Figure 3 shows the elemental mapping of chemical elemental components: all of them are in Figure 3a, and they are shown separately in Figure 3b-d, presenting the good chemical homogeneity of the material and highlighting the formation of ZnMg- and ZnY-based compounds. The XRD result for the Zn3 MgO.7Y alloy, as shown in Figure 3e, presented a main peak of \(\alpha\)-Zn and compounds formed with Mg and Y. The intermetallic compound YZn12, as shown by point 1 in Table 1, was identified and confirmed on the XRD chart along with other compounds, such as MgZn2, MgZn11, ZnMg, Mg12 ZnY and Mg2 Zn11, as discussed and analyzed in [20].  
Figure 2: Structural and chemical aspects of Zn3 MgO.7Y alloy: (**a**) SEM image at 500\(\times\); (**b**) SEM image at 2500\(\times\); (**c**) energy spectrum of the chemical elements identified on area (0.063 mm\({}^{2}\)) presented in the SEM image (**a**).