In-Situ Defect Spectroscopy of Al Welds During Mechanical Load Using a Scanning Positron Microbeam

我们项目的目标是帮助从根本上理解在原子水平上产生的材料缺陷与焊缝机械稳定性之间的关系。为此，我们想要在现场研究机械载荷作用下铝合金激光焊接和搅拌摩擦焊中缺陷的形成和分布。尤其是时效硬化合金，由于其高的抗拉强度、优异的耐腐蚀性和良好的焊接性，在航空航天工业中扮演着重要的角色。在焊接过程中，较大的热冲击和随后的快速冷却导致了空位形成、析出物溶解和部分缺陷退火的复杂相互作用。这又导致了复杂的显微组织，空位浓度、析出物浓度和晶粒细化的局部变化。强度的局部变化对焊接技术部件的机械回弹和寿命至关重要。空间分辨正电子束实验(空间分辨率~30微米)将被应用，因为它们特别适合于对工业合金中晶格缺陷及其元素环境的无损探测。在我们的实验中，我们将在CDB光谱仪的高强度正电子源NEPOMUC上使用独特的扫描正电子微束。铝试件的原位缺陷光谱将在从室温开始直到高温的拉伸和疲劳试验期间进行。我们还将应用辅助技术，例如显微切片的光学显微镜和显微维氏硬度的测量。通过这一技术，我们将能够将缺陷(如空位、空位-溶质原子复合体和沉淀物)的形成和分布与宏观性能(如抗拉强度和硬度)关联起来。我们预计，该项目的结果将对技术应用产生重大影响，不仅对焊接铝合金，而且对一般金属合金。从长远来看，我们希望将空间分辨正电子湮没谱建立为缺陷分析的强大工具，这在工程科学中对技术材料和部件的应用具有非常重要的意义，例如在造船、飞机和汽车工业中。

The goal of our project is to contribute to the fundamental understanding of the relation between material defects created on an atomic level and the mechanical stability of welds. For this purpose, we want to investigate in-situ the formation and distribution of defects in laser beam welds and friction stir welds of Al alloys during mechanical load. In particular, age-hardenable alloys – we will focus on AlCu6Mn – play an important role in aerospace industry due to their high tensile strength, excellent corrosion resistance and good weldability. During welding the large heat impact with subsequent rapid cooling results in a complicated interplay of vacancy formation, dissolution of precipitates, and partial defect annealing. This in turn results in a complex microstructure with a local variation of the concentration of vacancies, precipitates and grain refinement. The associated local variation of the strength is crucial for the mechanical resilience and the lifetime of the welded technical component. Spatially resolved positron beam experiments (spatial resolution ~30µm) will be applied because they are especially suited for the non-destructive exploration of lattice defects and their elemental environment in technical alloys. For our experiments, we will use the unique scanning positron-microbeam at the CDB spectrometer at the high-intensity positron source NEPOMUC. In-situ defect spectroscopy of the Al specimens will be performed during tensile and fatigue tests starting at room temperature up to high temperature. We will also apply complementary techniques, e.g. optical microscopy of the micro-sections and measurements of the micro-Vickers hardness By this, we will be able to correlate the formation and distribution of defects such as vacancies, vacancy-solute atom complexes, and precipitates with macroscopic properties like tensile strength and hardness. We expect that the outcome of this project will have a large impact for technical applications not only for welded Al alloys but for metallic alloys general. In the long term, we want to establish spatial resolved positron annihilation spectroscopy as a powerful tool for defect analysis that is of high importance in engineering science for the application of technical materials and components, e.g., in shipbuilding, airplane and automotive industry.