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

我们的项目的目标是有助于从根本上理解原子水平上产生的材料缺陷与焊接机械稳定性之间的关系。为此，我们想原位研究在机械载荷作用下，铝合金激光焊接和搅拌摩擦焊接中缺陷的形成和分布。特别是时效硬化合金-我们将重点关注AlCu 6 Mn-由于其高拉伸强度，优异的耐腐蚀性和良好的可焊性，在航空航天工业中发挥着重要作用。在焊接过程中，大的热冲击与随后的快速冷却导致空位形成、沉淀物溶解和部分缺陷退火的复杂相互作用。这反过来又导致了一个复杂的微观结构与空位，沉淀物和晶粒细化的浓度的局部变化。强度的相关局部变化对于焊接技术部件的机械弹性和寿命至关重要。空间分辨正电子束实验（空间分辨率~30µm）将被应用，因为它们特别适合于对工业合金中的晶格缺陷及其元素环境进行非破坏性探索。在我们的实验中，我们将使用高强度正电子源NEPOMUC的CDB谱仪上独特的扫描正电子微束。将在室温至高温的拉伸和疲劳试验期间对Al样本进行原位缺陷光谱分析。我们还将应用补充技术，例如显微切片的光学显微镜和显微维氏硬度的测量。通过这种方法，我们将能够将缺陷（如空位、空位-溶质原子复合物和沉淀物）的形成和分布与宏观性能（如抗拉强度和硬度）相关联。我们预计，该项目的成果将不仅对焊接铝合金，而且对一般金属合金的技术应用产生重大影响。从长远来看，我们希望将空间分辨正电子湮没光谱学建立为缺陷分析的有力工具，这在工程科学中对于技术材料和组件的应用具有高度重要性，例如，用于造船、飞机和汽车工业。

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.