Effect of Mn and Dispersoids on Grain Structure, Mechanical Properties and Crush Behavior of Extruded AA6082 Alloys
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In this study five different variants of an AA6082 aluminum alloy were investigated. The alloys have various amounts of Mn (0.006-1.172 wt%) and are homogenized in two different ways. After homogenization the billets got extrudet into rectangular-hollow profiles that were cooled using two different cooling rates (air-cooling and water-quenching). Further, the profiles were artificially aged to three different tempers (under-aged, peak-aged and over-aged). The effect of these parameters on microstructure, mechanical properties and crush performance of the various alloys in different states have systematically been studied. The materials microstructure were investigated by optical microscope and transmission electron microscope, mechanical testing was used to determine the stress-strain curves in uniaxial tension, and impact-testing and crush-testing was performed to investigate the energy absorption of the materials. Results from this study show that chemical composition, homogenization procedure, cooling rate after extrusion and artificial ageing influence the grain structure, mechanical properties and crush behavior of these AA6082-alloys to a large extent. Increased content of Mn and short holding time during homogenization increases the density of dispersoids. Dispersiods retard recrystallization after extrusion, but they also promote formation of precipitate free zones (PFZs) during ageing. The alloys show increasing strength up to ageing temper T6. The work-hardening is inverse proportional to the strength evolution during ageing. Ductility, impact energy and folding behavior are improved with increasing content of Mn, short holding time during homogenization and air-cooling after extrusion.