Rapid precipitation of dispersoids during extrusion of an Al–0.91 wt.% Mn–0.13 wt.% Zr–0.17 wt.% Sc-alloy

Abstract

Dispersoids are usually formed during precipitation annealing (homogenisation) of aluminium alloys in order to inhibit recrystallisation during subsequent processing and/or use at high temperatures. In this respect, Al 3(Sc x ,Zr 1− x )-dispersoids are most efficient, as they display the unique combination of rapid precipitation and slow coarsening. The objective of this work has been to investigate if a high recrystallisation resistance can be achieved during extrusion of an Al–0.91 wt.% Mn–0.13 wt.% Zr–0.17 wt.% Sc-alloy, without first subjecting the material to precipitation annealing, i.e. to study if a more efficient production route can be applied to produce profiles with fibrous/unrecrystallised structures. Success requires rapid formation of dispersoids during pre-heating of as-cast extrusion ingot. One variant was therefore pre-heated and extruded directly after casting. This variant was compared to an ingot which was first subjected to precipitation annealing. Both variants displayed similar extrudabilities and completely fibrous as-extruded microstructures with no signs of recrystallisation, i.e. a shorter process route (without precipitation annealing) can be applied for the investigated alloy.