Influence of trace elements with high vacancy binding energy on the precipitation hardening of Al-Cu-alloys

AlCu基合金作为航空机身的高强度轻质材料（AlCuMg、AlCuLi）和运输部门发动机缸体的铸造合金（AlSiCu）具有重要的应用。然而，向这些合金中添加微量元素可以显着提高其强度，而到目前为止，对成核的基本原子机制仅知之甚少。提高铝基材料的强度（时效硬化）是基于铝合金热处理期间或热处理后立即形成的空位扩散控制的沉淀物。因此，微量元素的高空位结合能对降水过程具有决定性影响。在这个项目中，我们将研究微量元素（< 0.1原子%，例如In，Sn，Sb，Pb，Bi）对形核的影响，从而对时效硬化行为的影响。从纯元素AlCu基合金的强度。这个项目的目的是关于微量元素，了解其空位结合现象的基本方面，作为其浓度和铝合金中结合强度的函数。为了揭示合金化以及微量元素与热处理中淬火空位之间的复杂相互作用，我们将采用几种补充方法，包括模拟工具。为此目的，所选微量元素的空位结合行为-在非合金纯铝的第一阶段-将通过正电子湮没光谱（PAS）进行检查，而X射线吸收光谱（XAFS）揭示了分解的非常早期阶段的铜原子和微量元素原子附近的短程有序。用电子探针分析（EPMA）研究了铝中微量元素的空间分布，以估计其在铝固溶体中的最大溶解度。为了确定Al-Cu-X合金的总析出顺序，对时效过程中析出相的形成和生长进行了更详细的研究。小角X射线散射（SAXS）将被用作一个特别有效的方法，在纳米范围内的沉淀动力学（粗化）的定量描述。由于析出物的尺寸和体积分数是负责的合金的强度/硬度，同时观察自然和人工时效过程中的硬度发展显着有助于了解微量元素对时效硬化的影响。基于对微量元素在沉淀物成核和生长过程中的作用所获得的知识，我们期望对改进现有的和新的时效硬化的锻造和铸造铝合金的发展做出重要贡献。此外，对微量元素的认识大大提高，导致再生铝在回收过程中的可用性大大提高。

AlCu-based alloys have important applications as high-strength light-weight materials for the fuselage in aviation (AlCuMg, AlCuLi) and as cast-alloys (AlSiCu) for engine blocks in the transport sector. However, adding trace elements to these alloys can significantly improve their strength, while the underlying atomic mechanisms of nucleation are so far only superficially understood. Increasing strength (age-hardening) in aluminium based materials is based on the vacancy-diffusion-controlled formation of precipitates during or immediately after the heat treatment of aluminium alloys. Hence, a high vacancy-binding energy of trace elements has a decisive influence on the precipitation process. In this project we are going to study the influence of trace elements (< 0.1 at% of e.g. In, Sn, Sb, Pb, Bi) on the nucleation and, thus, on the age-hardening behaviour resp. strength of AlCu-based alloys from pure elements. The aim of this project - concerning trace elements - is to understand basic aspects of their vacancy-binding phenomenon as a function of their concentration and their binding strength in aluminium alloys. To reveal the complex interplay between alloying as well as trace elements with quenched-in vacancies from the heat treatment, we will employ several complementary methods including simulation tools. For this purpose, the vacancy-binding behaviour of selected trace elements - in a first stage for unalloyed pure aluminium - will be examined by positron annihilation spectroscopy (PAS) while X-ray absorption spectroscopy (XAFS) reveals for the very early stages of decomposition the short-range order near copper atoms and atoms of trace elements. The spatial distribution of trace elements in aluminium will be investigated by electron probe micro analysis (EPMA) to estimate the respective maximum solubility in aluminium solid solution. Precipitates forming and growing during aging are examined in more detail in order to determine the total precipitation sequence of the Al-Cu-X alloy. Small-angle X-ray scattering (SAXS) will be employed as a particularly effective method for the quantitative description of the precipitation kinetics (coarsening) in the nanometer range. Since size and volume fraction of precipitates are responsible for the strength / hardness of the alloys, observing simultaneously the hardness development during natural and artificial aging contributes significantly to the understanding of the influence of trace elements on the age hardening. Based on the knowledge obtained on the role of trace elements during nucleation and growth of precipitates, we expect an important contribution to improve existing and to the development of new age-hardened wrought and cast aluminium alloys. Additionally, a significantly enhanced understanding of trace elements lead to a much better usability of secondary aluminium in recycling processes.