Microstructure- and mechanism-correlated characterization of the corrosion fatigue behavior of the creep-resistant magnesium alloys DieMag422 and AE42

为了在工业应用中安全有效地使用镁合金，特别是在汽车工业中，需要具有高蠕变和疲劳强度，并具有足够的耐腐蚀性。例如，用于齿轮箱和曲轴箱的材料必须承受高达200°C的温度。通过添加引起金属间相析出的特定合金元素，可以提高抗蠕变性能。然而，这些合金元素会在材料中形成微原电池，从而导致镁合金的耐腐蚀性下降。这些腐蚀应力反过来又降低了循环载荷下的使用寿命。因此，必须了解化学成分、抗蠕变性、抗腐蚀性和疲劳强度之间的相互依存关系，以改善材料和部件的性能。为了对镁构件进行可靠的设计和寿命计算，必须考虑腐蚀和循环载荷，以评估这些同时载荷对材料性能的影响。目前的研究主要针对腐蚀对疲劳行为的影响，但目前还没有针对应用进行优化的、特别是时间和成本效益的测试概念。在本研究项目中，将采用DieMag422和AE42两种抗蠕变镁合金原位研究腐蚀对疲劳行为的影响。为了对腐蚀疲劳行为进行比较表征，采用了一种新的测试策略，通过使用应用优化的物理和电化学传感器系统以及微观结构研究，以经济的测试次数提供详细的信息。获得的结果将用于开发基于模型的相关性，定量和定性地解释腐蚀-微观结构-性能关系。基于腐蚀和疲劳行为，该模型将用于可靠地估计考虑腐蚀载荷的疲劳强度和寿命性能。

For a safe and efficient use of magnesium alloys in industrial applications, particularly in automotive industry, a high creep and fatigue strength with a sufficient corrosion resistance is necessary. Materials, used e.g. for gearboxes and crankcases, have to withstand loadings at temperatures of up to 200 °C. The creep resistance can be improved by the addition of particular alloying elements which causes a precipitation of intermetallic phases. However, these alloying elements form micro-galvanic cells in the material which can result in a decrease of the corrosion resistance of magnesium alloys. These corrosive stresses, in turn, reduce the lifetime under cyclic loadings. Therefore, the interdependency between chemical composition, creep resistance, corrosion resistance and fatigue strength has to be known to improve material and component properties. For a reliable design and lifetime calculation of magnesium components, both corrosive and cyclic loadings have to be considered to evaluate the influence of these simultaneous loadings on the material properties mechanism-oriented. Current studies deal with the influence of corrosion on the fatigue behavior, but there are no application-optimized and especially time- and cost-efficient testing concepts provided.In the proposed research project, the influence of corrosion on the fatigue behavior will be investigated in-situ using two creep-resistant magnesium alloys DieMag422 und AE42. For a comparative characterization of the corrosion fatigue behavior, a new testing strategy is applied which provides detailed information by using an application-optimized physical and electrochemical sensor system and microstructural investigations with an economical number of tests. The obtained results will be used for the development of a model-based correlation interpreting the corrosion-microstructure-property-relationship quantitatively and qualitatively. Based on the corrosion and fatigue behavior, the model will be used to reliably estimate the fatigue strength and lifetime performance taking into account the corrosive loadings.