Improving Bendability of 6000-Series Extruded Aluminum Profiles Using Dies through Shear Stress and Flow-Velocity Reduction

Extruded profiles of Al-Mg-Si alloys are typically used in automotive applications. In this study, the microstructure of 6000-series alloys was improved in terms of the energy absorption property (bendability) using the shear stress and flow velocity generated during extrusion instead of conventional transition-metal alloying, because the latter presents challenges in reuse and recycling. This was accomplished using dies with different numbers of feeder holes. Furthermore, in a novel step, complementary finite element analysis (FEA) was conducted to investigate the effects of this improvement on microstructure strengthening. FEA results indicated that the profile obtained using the 4-hole die had lower internal shear stress distribution and aluminum flow velocity than using the 5-hole die. Cross-sectional electron backscatter diffraction observations revealed that the microstructure of the profile obtained using the 4-hole die had fine crystal grains and a strong internal cube or Goss preferential orientation, whereas that obtained using the 5-hole die exhibited coarse grains and an increased number of intermediate orientations. Consequently, the profile obtained using the 4-hole die exhibited improved bendability; furthermore, this die maintained the same tensile strength as the other specimen. Reducing the processing shear stress and flow velocity during extrusion allowed grain refinement and improved bendability at the same tensile strength.