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

对铝合金激光焊接过程中合金和工艺对凝固和组织形成的影响进行了经验研究和理论描述，并进行了实验验证。根据所获得的知识，可以影响工艺参数和合金成分，以改善焊缝的显微组织，从而提高抗热裂性、抗拉强度或抗蠕变性。激光粉末床熔合（LPBF）工艺与激光束焊接在许多方面都有联系。然而，与焊接相反，在LPBF过程中，凝固过程中形成的微观组织会影响整个部件，因此控制微观组织变得更加重要。因此，根据上述项目专家报告的建议，本提案旨在建立在先前焊接研究成果的基础上，并将其转移到LPBF中普遍存在的边界条件和由此产生的微观结构。该项目的目标是确定和控制过程、环境和合金对LPBF生产的铝合金部件从定向到等轴晶粒生长的转变、晶粒尺寸和枝晶臂间距的影响。这将范例地通过使用沉淀硬化合金和自硬化合金来实现。与目前的技术相比，为了实现更高的建立速率，需要使用比目前工业上实现的更高的激光功率（MPA高达2 kW， IFSW高达16 kW）。基于之前项目所获得的知识和研究现状，对LPBF过程的理解逐渐加深，描述晶粒结构的模型得到扩展：i)单轨内，ii)层内，iii)多层。这些不同的尺度增加了要考虑的关系的复杂性，也增加了对过程进行更深入理解所需的模拟方法的复杂性。因此，本项目的目的是发展和实验验证对工艺材料的更深入理解。

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.