## 3 Results
### Microstructure--Corrosion Condition  
Selected light and electron microscopic images, as well as EDS, and Fourier-transform infrared spectroscopy (FTIR) scans, are examined to evaluate both test strategies. Figure 6 shows an overview image of a sample without polarization (i\({}_{\text{corr}}\)) and one for each polar  
Figure 5: Results of immersion tests with galvanostatic polarization on Mg WE43 in a modified minimum essential medium at 36.5 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Current Density i** & **Mean Dissolution Rate \(\dot{\text{m}}_{\text{diss,mean}}\)** & **Coefficient of Determination R\({}^{2}\)** \\ **(mA cm\({}^{-2}\))** & **(mg cm\({}^{-2}\) a\({}^{-1}\))** & **(10\({}^{-2}\))** \\ \hline i\({}_{\text{corr}}\) & \(3.44\cdot 10^{1}\) (m\({}_{\text{corr,mean}}\)) & 76.555–97.428 \\ \hline
0.5 & \(7.51\cdot 10^{2}\) & 98.205 \\ \hline
1 & \(1.27\cdot 10^{3}\) & 99.490 \\ \hline
2 & \(2.97\cdot 10^{3}\) & 99.533 \\ \hline
20 & \(3.66\cdot 10^{4}\) & 99.932 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summarized results of immersion tests on Mg WE43 in a modified minimum essential medium at 36.5 \({}^{\circ}\)C.  
ization step. For the experiments without polarization, a relatively uniform corrosion layer is obtained whereby the edge areas of the embedded sample are less affected. Exemplary for the unaccelerated tests, Figure 7a shows a SEM image of the corrosion layer, exhibiting a uniform, cracked corrosion morphology typical for magnesium. Brighter circular and stick-like inclusions can be seen in the layer, indicating enrichments by the alloying elements. Circular and spherical formations are also deposited on the layer, arranging themselves in circles of different diameters around the sphere. For the analysis of these formations, Figure 8a displays a SEM image with plotted EDS points, Figure 9a shows the corresponding atomic percentages of the elements magnesium (Mg), oxygen (O), phosphorus (P), calcium (Ca), and carbon (C) and an analysis of the molecular compounds in Figure 9b. These figures illustrate that for the deposits, compared  
Figure 6: Light microscopic images of Mg WE43 after immersion in a modified minimum essential medium at 36.5 \({}^{\circ}\)C with and without galvanostatic anodic polarization. Figure 7: Microstructural investigations on Mg WE43 after immersion in a modified minimum essential medium at 36.5 \({}^{\circ}\)C: (a) 48 h at i\({}_{\text{corr}}\); (b) and (c) with galvanostatic polarization at i\({}_{\text{a}}\) = 1 mA cm\({}^{-2}\). to the homogeneous corrosion layer, the percentage of O, Ca, and P increases, and the percentage of Mg decreases. Figure 8b shows a FTIR scan after unaccelerated corrosion and, as an example, after accelerated corrosion (i\({}_{\text{a}}\) = 0.5 mA cm\({}^{-2}\)) with the absorbance A plotted over the wavenumber \(\overset{\sim}{\text{v}}\). In general, the peaks occurring at 1500, 1401, 1030, 851, and 556 cm\({}^{-1}\) are similar for both testing strategies, except a broader activity between 3630 and 2460 cm\({}^{-1}\) occurring only for accelerated corrosion. The deposit's morphology cannot be found in the experiments with polarization. Figure 8b shows a different structure without a circular or spherical formation. Rather it can be described as a volcanic structure. Besides the large uniform corrosion layer in Figure 6 (i\({}_{\text{corr}}\)), a corrosion pit is recognizable. This could also be observed for the other samples of the immersion tests without polarization. For the accelerated immersion tests, the number of locally intensified corrosion increases with increasing anodic current density. Figure 7b,c show exemplary SEM images of the corrosion morphology for a current density of i\({}_{\text{a}}\) = 1 mA cm\({}^{-2}\). Between the corrosion pits (Figure 7b), areas with a homogeneous corrosion morphology are visible (Figure 7c), comparable to the unaccelerated tests (Figure 7a). Furthermore, the degree of degradation decreases with increasing distance to the center of the corrosion pits.