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高效地使用镁合金，特别是在汽车工业中，需要具有高的蠕变和疲劳强度以及足够的耐腐蚀性。用于齿轮箱和曲轴箱的材料必须承受高达200°C的载荷。通过添加导致金属间化合物析出的特殊合金元素，可以提高蠕变抗力。然而，这些合金元素会在材料中形成微原电池，从而导致镁合金耐蚀性的降低。这些腐蚀性应力反过来又降低了循环载荷下的寿命。因此，必须了解化学成分、抗蠕变、耐腐蚀和疲劳强度之间的相互依赖关系，以改善材料和部件的性能。为了对镁合金构件进行可靠的设计和寿命计算，必须同时考虑腐蚀载荷和循环载荷，以便从机理上评估这些载荷对材料性能的影响。目前的研究主要集中在腐蚀对疲劳行为的影响上，但还没有针对实际应用进行优化，尤其是时间和成本效益较高的测试概念。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，该策略通过使用针对应用优化的物理和电化学传感器系统以及通过经济的测试次数进行微观结构研究来提供详细信息。所获得的结果将用于开发基于模型的相关性，以定量和定性地解释corrosion-microstructure-property-relationship。基于腐蚀和疲劳行为，该模型将被用于在考虑腐蚀载荷的情况下可靠地估计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.