Microstructure control and extrudability of Al–Mg–Si alloys microalloyed with manganese

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Abstract
The hot deformation of AA 6063 and AA 6005 Al alloys has been related to chemical composition and the microstructural evolution occurring during the various heat treatment procedures before extrusion. It was shown that a small addition of Mn significantly accelerates the homogenising process (transformation of the brittle platelike β-AlFeSi phase to the more rounded α-AlFeSi phase) which results in superior hot formability and ductility. The mechanical behaviour of Al–Mg–Si alloys during hot deformation can be explained in terms of a model of dislocations climbing around particles. Large β phase particles increase initial work hardening rate and flow stress and impair hot ductility. The hot ductility of the material investigated via tensile testing was found to correlate with the density of particles covering grain boundaries. It was also shown that grain refinement in the billet leads to more uniform distribution of intermetallic constituents, which accelerates the homogenising process and improves the hot ductility. Full scale extrusion trials show that the results from hot formability tests in the laboratory correlate closely with the relative extrudability of the investigated alloys. MST/1877