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镁合金WE 43并进一步开发。与项目第一阶段的DieMag 422和AE 42镁合金相比，该合金具有更高的机械强度和允许工作温度。在WE 43合金的典型应用领域（例如航空航天和赛车运动）中，循环蠕变非常重要。在项目的第一阶段，很明显，只有通过系统研究微观结构的影响，才能完全识别蠕变和失效机制，并了解它们的相互作用和演变。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-粉末床熔融（L-PBF）中的铸造（低冷却速率和大晶粒尺寸）和增材制造（高冷却速率和小晶粒尺寸）这两种制造工艺旨在产生两种不同的微观结构状态，比较它们，并分离机制。虽然铸造的WE 43已经用于汽车和航空航天应用，但增材制造的WE 43还没有。在调查的框架内，两个制造过程及其产生的微观结构对循环蠕变行为的影响，因此，应被表征以及微观结构和机制为导向的评估和描述的基础上的数学模型。科学目的是将微观结构（例如晶粒尺寸、沉淀、硬化、软化行为）和工艺相关缺陷（例如气孔和收缩孔隙、粘结缺陷）与循环蠕变性能（例如疲劳强度、循环蠕变速率）相关联。在项目第一阶段开发的测试设备已经设计用于更高的测试温度和力，并且测试方法将不断进一步开发。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，应分析和理解在有和没有叠加疲劳载荷的情况下材料行为的方向相关差异。静态蠕变的机制应该从循环蠕变中分离出来，以便提供关于它们之间相互作用和演变的信息。使用扫描电子显微镜和计算机断层扫描，微观结构和选定的疲劳试样的缺陷的影响将进行调查，以确定如何最大限度地提高其寿命的过程中引起的微观结构。最后，该项目第一阶段和第二阶段的结果将结合起来，并通过铸造和增材制造的WE 43合金扩展所产生的相关模型。

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.