Open Collections

Zang, Andrew

University of British Columbia

The use of hollow 6xxx series Al-Mg-Si alloys in the automotive industry is steadily increasing due to the potential to reduce vehicle weight and lessen in-use emissions. To extrude a hollow shape, porthole dies are often employed, which result in longitudinal weld seams of disturbed microstructure and crystallographic texture, as well as variable mechanical properties. In this research, extrusion through a simple porthole die was studied. The alloy used in this work contained Mn and Cr, which in combination with the lower extrusion temperature of 400 °C, produced a material that was largely unrecrystallized. Throughout the process, i.e. starting from the billet and ending in the extrudate, crystallographic texture was tracked and simulated along the 2D horizontal symmetry plane of the die via finite element method (FEM) predicted material flow paths. This was accomplished by using electron backscatter diffraction (EBSD) to characterize the partially extruded material, which was quenched and extracted during extrusion. Texture predictions were conducted using a soft-coupled FEM/visco-plastic self-consistent (VPSC) approach. The results showed that the texture could be simulated up to 1.4 mm away from the weld seam using the thermomechanical history of the material as input. Closer than 1.4 mm, texture prediction is limited, and the interaction of the billet with the extrusion die leads to high levels of redundant work. After the die exit, an additional bridge geometry was studied. It was observed through metallographic analysis that the microstructure near the weld seam of the extrudates displayed a disturbed pattern which differed for each bridge. Micro-scale digital image correlation (DIC) revealed that when deformed perpendicular to the weld seam, patterns of local plasticity developed. EBSD was used to characterize the unique regions of crystallographic texture near the weld seam, and the mechanical response was simulated using VPSC with the textural data as input for each bridge case. The simulated properties were then fitted with the Barlat YLD2004-18p anisotropic yield function and implemented into FEM simulation. The resulting FEM predicted strain maps matched the localization observed using DIC for both bridge cases, thus establishing crystallographic texture as the dominant factor affecting local plasticity.

Text

2024-08-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89002

Materials Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/