Papers by Author: Y. Langsrud

Abstract: In the present work, three-point bending tests have been performed on four commercially extruded 6xxx- and 7xxx alloys, one with a fibrous and one with a recrystallized grain-structure for each alloy class, with the bending axis orientated 0, 45 and 90° with respect to the extrusion direction. Microstructure and texture characterization as well as tensile testing of the same materials have been performed and correlated with the bending results. In general there is good agreement between the bending angle and the fracture strain for all alloys, with the highest values in the extrusion direction. However, there are no indications in the microstructure and texture that explain the large differences in bendability observed. Die lines and recrystallized layer on a fibrous alloy have been removed to investigate their effect on the bending behaviour. However, these effects also seem to be limited, and cannot explain the anisotropy effects observed in bending angles.

Abstract: Solid solution treatment at 450°C and 550°C and subsequent two step age hardening at 100°C and 150 °C up to 144 hrs. have been carried out for two conventional and four experimental 7xxx type of alloys with different Mg, Zn, Fe and Si content. The influence of silicon on phase and kinetics of age hardening zones and particles has been followed. Increase in silicon required higher solid solution temperature in order to achieve reasonable age hardening response. High silicon alloys, solid solution treated at high temperature, have tendency to recrystallize during aging. The GP-zone formation is affected by the ratio between Mg, Zn and Si. In alloys with Mg/Zn ratio in the range 1:2 GP(I)-type zones are formed, at higher solid solution temperature also GP(II); low Mg-content favor GP(II)- zones. In high silicon alloys GP-zones of b’’’-type (from the Al-Mg-Si) system contribute to age hardening. The precipitation kinetics of the main hardening phase h’, is influenced by the preceding GP-zone stage.