The Influence of Si and Mg Content on the Microstructure, Tensile Ductility, and Stretch Formability of 6xxx Alloys

In this study, the effect of Si and Mg content on the microstructure, tensile ductility, and stretch formability of naturally aged Al-Mg-Si alloys has been investigated using optical microscopy, scanning electron microscopy, tensile testing, forming limit diagram tests, and various modeling approaches. The results show that by raising the Si content in the alloy, the tensile ductility and stretch formability can be improved. By contrast, increasing the Mg content in the alloy has little influence on the tensile ductility and stretch formability. The results are discussed in terms of the effects of microstructural features such as solutes, clusters, and dispersoids on the work-hardening and strain rate-hardening behavior of the materials. Furthermore, thermodynamic modeling is employed to predict microstructures that could improve the stretch formability of the high Mg content alloy.