Local microstructural evolution, interfacial integrity and rate effects associated with modern joining processes using plastic deformation

该项目考虑了碰撞连接后连接区的微观组织演变和相应的性能变化。这个过程与高度变形有关。此外，接合在非常高的速度下发生。因此，需要在高应变率条件下系统地表征材料行为，作为连接过程本身模拟的基础。该项目建立在与优先计划的加工项目密切合作的基础上，在定制的简化实验装置中以及在接近工业过程的更现实的加工条件下研究碰撞连接过程。这些合作提供了丰富的样品，允许详细的微观结构和微观力学研究。分别使用（技术上）纯铝以及钢和铝的组合的接头，研究了不同初始微观结构和表面条件的影响。最近的研究结果详细记录了特征性波浪形连接区的形成。此外，基础材料的动态材料行为的特点，以支持合作伙伴项目中的数值模拟。仔细的微观结构研究表明，连接区通常由薄的区域组成，甚至可能在连接过程中短暂熔化。随后的非常快速的冷却导致再结晶的快速凝固区域。当前和未来研究的重点是了解这些连接区域的特殊形态如何受到不同工艺参数的影响，它如何影响接头的强度和完整性，以及典型的加工窗口如何反过来受到相应的基本微观结构过程的限制。该项目将继续提供具有良好定义的初始微观结构的材料用于碰撞连接，并表征这些基础材料的动态材料行为。该项目的研究将主要集中在通过电子显微镜对连接区的微观结构表征，以及对局部机械表征的补充纳米压痕调查。这里提出的研究还将有助于分析优先计划的两个主要课题（塑性变形连接过程中的结合机制和高应变率材料行为）。

This project considers microstructural evolution and the corresponding changes of properties in joining zones after collision joining. This process is associated with high degrees of deformation. Moreover, joining occurs at very high velocities. Therefore, the material behavior needs to be characterized systematically under high strain rate conditions as a basis for the simulation of the joining process itself. The project builds on close collaborative work with processing-oriented projects of the Priority Programme, where the collision joining process is studied both in a custom-made, simplified experimental setup, and under more realistic processing conditions close to the industrial process. These collaborations provide a wealth of samples that allow for detailed microstructural and micromechanical investigations. Using joints of (technically) pure aluminum and a combination of steel and aluminum, respectively, the effect of different initial microstructures and surface conditions is investigated. Recent results document in detail the formation of characteristic, wavy joining zones. Moreover, the dynamic material behavior of the base materials is characterized to support numerical simulations in the partner projects. Careful microstructural investigations indicate that the joining zones typically consist of thin regions that may even have briefly melted during joining. The subsequent, very rapid cooling results in recrystallized, rapidly solidified regions. The focus of current and future research is placed on understanding how the special morphology of these joining regions is affected by different processing parameters, how it influences strength and integrity of the joints, and how the typical processing windows are in turn limited by the corresponding fundamental microstructural processes. The project will continue to provide materials with well-defined initial microstructures for collision joining, and to characterize the dynamic material behavior of these base materials. The research of this project will be primarily focused on microstructural characterization of the joining zones by electron microscopy, and on complementary nanoindentation investigations for local mechanical characterization. The investigations propsed here will also contribute to an analysis of two main topics (bonding mechanisms during joining by plastic deformation and high strain rate material behavior) of the Priority Programme.