## 4 Discussion  
The initial microstructure exhibits a high number of evenly distributed precipitates of alloying elements. These occur as intermetallic compounds inhomogeneous in size and shape (Figure 2). Besides the \(\alpha\)-Mg matrix, the microstructure consists of a second phase Mg\({}_{12}\)(RE), accumulating at the grain boundaries, a stick-like \(\beta\)-phase within the matrix (Mg\({}_{14}\)Nd\({}_{2}\)Y), as well as yttrium-rich (MgY, Mg\({}_{14}\)Y\({}_{5}\), Mg\({}_{24}\)Y\({}_{5}\)), neodymium-rich (Mg\({}_{41}\)Nd\({}_{5}\), Mg\({}_{12}\)Nd), and zirconium-rich precipitates [23; 29; 30]. In general, rare earth elements are considered to have a passivating effect on the corrosion behavior of magnesium (Mg) alloys [5]. However, inhomogeneous microstructures tend to cause corrosion pits due to micro-galvanic effects [31]. For alloy WE43, this is mainly favored by the accumulation of yttrium- and zirconium-rich precipitates [30]. To what extent both effects influence each other and which one dominates will be explained in the following discussion. Potentiodynamic polarization (PDP) allows a first estimation of the corrosion rate \(\dot{\mathrm{m}}_{\mathrm{corre}}\) and a qualitative corrosion behavior. The determined corrosion current densities \(\dot{\mathrm{i}}_{\mathrm{corr}}\) and the estimated corrosion rate (Table 2) are comparable to those found in the literature [23; 29; 32]. The qualitative course of the anodic branch demonstrates moderate polarizability (Figure 3). Furthermore, the flattening near the open circuit potential (OCP) indicates the formation of a passive layer, which disrupts as the potential increases accompanied by increased noise and passes into the pronounced active area with strong anodic dissolution. Consequently, the course of the anodic branch supports the thesis of a passivating corrosion behavior [32]. Based on the corrosion current density, as well as the anodic branch, four polarization steps are chosen for the immersion tests with galvanostatic polarization (0.5, 1, 2, and 20 mA cm\({}^{-2}\)). To compare both test strategies, the results of unaccelerated corrosion are discussed first. The course of the hydrogen evolution exhibits a reduction of the slope and suggests a passivating corrosion behavior of the alloy Mg WE43 (Figure 4). In general, the course is comparable to other studies that investigated Mg WE43 [9; 11]. In a study by [PERSON] et al., a qualitatively and quantitatively similar course was observed on the same alloy composition [10]. Here, the course between the two regression lines becomes clearer. Considering the corrosion morphology, an accumulation of brighter areas in the corrosion layer is recognizable, indicating the inclusion of alloying elements with higher density (Figure 7). These inclusions are accompanied by a slight change in the Pilling-Bedworth ratio (PBR) and lead to higher oxide layer stability [33]. This value describes the ratio of the molar volumes of the metallic element and the respective oxide and is PBR = 0.81 for magnesium/magnesium oxide. According to the definition, values PBR < 1 lead to cracking of the oxide layer and do not provide sufficient protection of the subjacent substrate material [24]. The layer's cracking can also be observed in the electron microscopic images. Nevertheless, the course of hydrogen evolution and the inclusion of alloying elements in the corrosion layer suggest a change in PBR, and consequently, an increase in the layer stability [33]. Besides the extensive homogeneous corrosion morphology, the samples of unaccelerated corrosion show locally intensified corrosion (Figure 6). According to current literature, these are due to increased accumulations of the alloying elements yttrium and zirconium [11; 33]. By measuring the Volta potential, [PERSON] et al.