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

• Applicant: Professor Dr.-Ing. Frank Walther
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2016 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 317233119

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.

• DFG Programme: Research Grants