Modell-based Characterization of the Fatigue Behavior of Additively Manufactured Al-Si-Mg Aloys, Considering the Interrelation of Defects, the α-Al Solid Solution and the Si Network

• Applicants: Dr.-Ing. Bastian Blinn; Professor Dr.-Ing. Frank Walther
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Materials in Sintering Processes and Generative Manufacturing Processes
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 583077280

Producing structural components via laser-based powder bed fusion (PBF-LB) promises an enormous lightweight potential. In this context light metals, i.e., Al-Si-Mg alloys, are highly relevant. To optimize these components, a sound knowledge of the additively manufactured microstructure and the resulting mechanical properties is indispensable. The high cooling rates caused by PBF-LB lead to a cellular microstructure of Al-Si-Mg alloys, consisting of α-Al solid solution cells surrounded by a Si network. The variation of the PBF-LB parameters influences the cooling rates, and hence, the cellular structure. Own works and results available in literature clearly show that the cellular structure leads to a higher strength in relation to casted Al-Si-Mg alloys. Moreover, it is indicated that the geometry and the local mechanical properties of the α-Al solid solution cells are crucial for the global deformation behavior. Consequently, a sound knowledge of the relation between the cellular structure with the monotonic and cyclic deformation behavior is elaborated in this project. For this, different conditions of AlSi7Mg and AlSi12Mg are produced by variation of the laser power and scan speed. These conditions will vary in the geometry of the cellular structure, and in the local mechanical properties of the α-Al solid solution cells. The latter is analyzed by cyclic nanoindentation testing. In addition to these conditions, two variants of AlSi10Mg, which were investigated in previous work, are analyzed. In addition, to separate the effect of precipitation hardening a non-hardenable alloy is taken into account. Based on the analyses performed at all these different conditions, the influence of the Si content and the PBF-LB process parameters on the cellular structure, including the mechanical properties of the cells, are examined. From the parameter analyses on AlSi7Mg and AlSi12Mg, two conditions are selected, respectively. In analogy to the previous work on AlSi10Mg, tensile and fatigue tests are planned for these four conditions to analyze the influence of the cellular structure on the deformation behavior. Furthermore, the aim of the project is the analysis of the impact of the cellular structure on the failure mechanisms in the very (VHCF) and high cycle fatigue (HCF) regime. For this, intermitted fatigue tests at specimens with artificial defects are performed, respectively. In these tests a special focus is placed on the interaction of the cellular structure with the crack-initiating defects, including the geometry and properties of the α-Al solid solution cells. At least the resulting defect tolerance will be evaluated considering this interaction. Based on the investigations described, the defect-based fatigue behavior of Al-Si-Mg alloys is modelled, considering the process-induced defects, the cellular structure and the local mechanical properties of the cells.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Tilmann Beck