Mechanism-oriented characterization of the microstructural and load direction-dependent cyclic creep (ratcheting) behavior of the magnesium alloy WE43

该项目第二阶段的目标是将成功验证的测试策略应用于高强度和抗蠕变的镁合金WE43，并进一步开发。与项目第一阶段采用的DieMag422和AE42镁合金相比，该合金表现出显著更高的机械强度和允许的工作温度。在WE43合金的典型应用领域(如航空航天和赛车运动)，循环蠕变是非常重要的。在项目的第一阶段，非常明显的是，只有通过系统地研究微观结构的影响，才有可能完全识别蠕变和破坏机制，以及了解它们的相互作用和演化。因此，必须考虑工艺、结构、材料性能和损伤之间的相互关系。因此，激光-粉床熔化的两种制造工艺：铸造工艺(低冷却速率和大颗粒尺寸)和添加制造工艺(高冷却速率和小颗粒尺寸)旨在产生两种不同的组织状态，并对它们进行比较，并分离机理。因此，在研究的框架内，应该表征这两种制造工艺及其产生的组织对循环蠕变行为的影响，并基于数学模型进行面向微观组织和机制的评估和描述。其科学目标是研究显微组织(例如，晶粒度、析出物、硬化、软化行为)和与工艺相关的缺陷(例如，气孔和缩松、结合缺陷)与循环蠕变性能(例如，疲劳强度、循环蠕变速率)之间的关系。该项目第一阶段开发的测试设备已经针对更高的测试温度和力进行了设计，测试方法将继续得到进一步开发。在静态拉伸和压缩蠕变试验以及拉伸和压缩模式下的单步和多步疲劳试验中，应分析和了解在有和没有叠加疲劳载荷的情况下材料性能的方向上的差异。应将静态蠕变机制与循环蠕变机制分开，以便提供关于它们相互作用和演化的信息。利用扫描电子显微镜和计算机断层扫描技术，研究选定的疲劳试件的组织和缺陷对其寿命的影响，以确定如何通过工艺诱导的组织来最大化疲劳试件的寿命。最后，项目第一阶段和第二阶段的结果将结合在一起，所产生的相关模型将通过铸造和添加剂制造的WE43合金来扩展。

The aim of the second phase of the project is the application and further development of the successfully validated test strategies to the high strength and creep resistant magnesium alloy WE43. Compared to the DieMag422 and AE42 magnesium alloys characterized in the first phase of the project, this alloy exhibits significantly higher mechanical strength and permissible operating temperature. In the typical field of applications of the WE43 alloy (e.g. aerospace and motorsports) cyclic creep is of significant importance. In the first phase of the project, it became very obvious that a complete identification of the creep and failure mechanisms as well as an understanding of their interaction and evolution are only possible by a systematic investigation of the influence of the microstructure. Consequently, the interrelation between process, structure, material properties and damage must be considered. Therefore, the two manufacturing processes of casting (low cooling rate and large grain size) and additive manufacturing (high cooling rate and small grain size) in laser-powder bed fusion (L-PBF) are intended to produce two different microstructural states, compare them, and separate the mechanisms.While the casted WE43 has already been established for automotive and aerospace applications, the additively manufactured WE43 is not. Within the framework of the investigations, the influences of the two manufacturing processes and their resulting microstructures on the cyclic creep behavior should, therefore, be characterized as well as microstructure- and mechanism-oriented evaluated and described based on mathematical models. The scientific aim is the correlation of the microstructure (e.g. grain size, precipitation, hardening, softening behavior) and process-related defects (e.g. gas and shrinkage porosity, bonding defects) with the cyclic creep properties (e.g. fatigue strength, cyclic creep rates). The test devices developed in the first phase of the project are already designed for the higher test temperatures and forces and the test methods will be consistently further developed. Within static tension and compression creep tests as well as single- and multi-step fatigue tests in tensile and compression modes, the direction-dependent differences in material behavior with and without superimposed fatigue loading shall be analyzed and understood. The mechanisms of static creep should be separated from cyclic creep in order to provide information on their interaction and evolution. Using scanning electron microscopy and computed tomography, the influence of microstructure and defects of selected fatigue specimens will be investigated to determine how to maximize their lifetime by the process-induced microstructure. Finally, the results of the first and second phases of the project will be combined, and the resulting correlation models will be expanded by the casted and additive-manufactured WE43 alloy.