Influencing the microstructure of aluminum alloys in additive manufacturing by laser powder bed fusion in process regimes of highest deposition rates at several kW laser power

• Applicants: Professor Dr. Thomas Graf; Professor Dr.-Ing. Stefan Weihe
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Joining and Separation Technology ; Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398552773

The alloy and process influences on the solidification and the microstructure formation during laser beam welding of aluminum were both investigated empirically and described theoretically and were verified experimentally in the previous project. Based on the obtained knowledge, it is possible to influence the process parameters and the alloy composition in order to improve the microstructure of the weld for an increased hot cracking resistance, tensile strength or creep resistance. The process of laser powder bed fusion ("LPBF") is related to laser beam welding in many aspects. As opposed to welding, however, the microstructure formed during solidification in the LPBF process affects the entire component, which makes it even more important to control the microstructure. As recommended in the expert report of the above-mentioned project, this present proposal is therefore intended to build on the previous research results on welding and transfer them to the boundary conditions prevailing in LPBF and the resulting microstructure. The goal of the project is to determine and control the process, environmental and alloying influences on the transition from directional to equiaxed grain growth, on grain size and on dendrite arm spacing in aluminum alloy components produced by LPBF at highest build-up rates. This is to be implemented exemplarily by using a precipitation hardening alloy and a self-hardening alloy. In order to achieve significantly higher build-up rates compared to the state of the art, considerably higher laser powers are to be used (MPA up to 2 kW, IFSW up to 16 kW) than can currently be implemented industrially. Based on the knowledge gained from the previous project and the state of the art in research, the understanding about the LPBF process is gradually deepened and the models for describing the grain structure are extended: i) within a single track, ii) within a layer, and iii) over multiple layers. These different scales increase the complexity of the relationships to be considered and also the complexity of the simulation methods needed to gain a deeper understanding of the process. Therefore, the aim of the presented project is to develop and experimentally verify a deeper understanding of the process-material.

• DFG Programme: Research Grants