Improvement of the application characteristics of multi-layered sheet material for forming technology produced via Accumulative Roll Bonding

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392174229

A key approach to reducing CO2 emissions in the automotive sector is the establishment of innovative lightweight design concepts both for the actual reduction of emissions in vehicle operation and for increasing resource efficiency by reducing material consumption. Aluminum alloys of the 6000 series are characterized by their high specific strength and are therefore already used for structural and outer skin applications in modern vehicle construction. The lightweight potential of these sheets can be increased by an additional increase in material strength. Beside varying the alloy composition and the heat treatment strategy, this can also be implemented by mechanical processes. In this context, the Accumulative Roll Bonding (ARB) process is worth highlighting, as it can be used to produce large-scaled and high-strength sheet products. In the ARB process, high degrees of deformation are induced through repeated stacking and rolling of the sheets, resulting in an ultrafine-grained microstructure. An important process step in the ARB process is the surface treatment of the contact areas. This is necessary to remove the bond-inhibiting oxide layer and to increase the roughness of the surface. A high roughness level has already been identified as being beneficial for the cold welding between the interfaces in the rolling gap. A decisive challenge is the reproducibility and homogeneity of the surface treatment and the associated surface properties, which could not be realized yet by manual treatment methods. The overall objective of the project is to investigate the continuous manufacturability of multilayered AA6014 sheets by fundamental analysis of the bond formation mechanisms. However, this requires a process-stable surface treatment strategy, which is implemented with a robot-assisted wire brushing station. This enables the fundamental research of the relationships between the surface and near-surface material properties such as strain hardening, residual stresses and oxide layer thickness with the resulting bond properties of the multilayered sheets. The failure analyses with regard to crack formation and delamination by means of mechanical characterization tests aim to derive an advantageous process window for the surface treatment. Cracking is predominantly dependent on the ductility of the multilayered material. Therefore, a sub-objective is to determine the dependence of ductility on the number of ARB rolling cycles for the investigated AA6014 alloy. In addition, with the target of improving the continuity of the ARB process in the future, the process step of sheet-leveling will be investigated. The aim is to analyze the influence of the straightening process on the interfacial joints in multilayered ARB sheets. The research project provides the foundation for a future improvement of the ARB process design as well as the formability of the resulting semi-finished products.

• DFG Programme: Research Grants