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

在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都是经验研究和理论描述的，并在以前的项目中进行了实验验证。根据所获得的知识，可以影响工艺参数和合金成分，以改善焊缝的微观结构，从而提高耐热裂性、抗拉强度或抗蠕变性。激光粉末床熔合（“LPBF”）工艺在许多方面与激光束焊接相关。然而，与焊接相反，在LPBF工艺中固化期间形成的微观结构会影响整个部件，这使得控制微观结构变得更加重要。正如上述项目的专家报告中所建议的那样，本提案旨在建立在以前关于焊接的研究结果的基础上，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工艺、环境和合金化对从定向到等轴晶粒生长的过渡、对晶粒尺寸和对LPBF以最高构建速率生产的铝合金部件中的枝晶臂间距的影响。这将示例性地通过使用沉淀硬化合金和自硬化合金来实现。为了实现与现有技术相比明显更高的累积速率，将使用比目前工业上可实现的功率高得多的激光功率（MPA高达2kW，IFSW高达16kW）。基于从先前项目中获得的知识和研究的最新技术，对LPBF过程的理解逐渐加深，并且用于描述晶粒结构的模型被扩展：i）在单个轨道内，ii）在一个层内，和iii）在多个层上。这些不同的尺度增加了要考虑的关系的复杂性，也增加了更深入地理解过程所需的模拟方法的复杂性。因此，本项目的目的是开发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.