Verbesserung der Umformbarkeit von Al-Mg-Si-Legierungen für Automobilaußenhautanwendungen

Al-Mg-Si alloys represent an important class of materials for use as outer body sheet in automotive manufacturing, but they compete with more cost¿effective deep¿drawing steels. While aluminum (Al) clearly offers the advantage of significant weight reduction compared to steel, it shows certain disadvantages, particularly with respect to formability. The aim of this work is therefore to improve the formability of Al-Mg-Si alloys through practical adjustments to the chemical composition as well as the thermomechanical process parameters. The focus lies on analyzing how microstructural constituents, such as primary phases, dispersoids, precipitates, and texture, affect formability. Laboratory tests (tensile test, hemming test) are combined with deep-drawing experiments using an industry¿relevant tool for characterization. The evaluation of the strain¿hardening behavior using Kocks¿Mecking plots provides a first important assessment of performance in the deep¿drawing process. While primary phases and dispersoids mainly increase initial work hardening, dissolved Si and Mg atoms influence the progression of the plot. A delayed dynamic recovery causes the hardening rate to decline more slowly with increasing deformation, thereby postponing failure by necking due to plastic instability. Strain¿rate sensitivity is traditionally considered less important for the formability of aluminum. However, tests with different drawing speeds reveal interesting effects, with higher Si content again showing positive influence. Regarding hemmability, other influencing factors become more important than for deep drawability, as it is a process dominated by fracture behavior. In addition to the primary phases whose morphology is affected by Mn content, the homogenization and rolling processes, the texture plays a central role.