Local Approach to High Temperature Ductility Modeling in 6XXX Aluminium Alloys

Low and medium strength AlMgSi alloys are commonly used for hot extrusion. For high productivity it is necessary to obtain the alloy in a soft condition so that the extrusion rate can be increased without overloading the press. Such AlMgSi alloys can be considered as two phase alloys in which one phase is the Al matrix and the second one is constituted by different particles among which the Fe rich intermetallics. The second phase particles may have important consequences on the deformation process, because not only they affect the flow stress of the material, but also they are likely to influence the ductility and change the final microstructure. In the case of commercial aluminium extrusion alloys, a homogenisation heat treatment of the as-cast material is required to improve ductility and enable efficient extrusion. The optimisation of such extrusion processes depends on a thorough understanding of the homogenisation kinetics and, in particular, of the morphological evolution of the intermetallic inclusions during the homogenisation process. Moreover damage initiation occurs in such alloys by decohesion or fracture of inclusions as referred by Toda and Kobayashi [

1

]. By performing a long homogenisation heat treatment at a sufficiently high temperature, during which the -Al5FeSi phase transforms to the more rounded meta-stable cubic -Al12(FeMn)

3

Si phase or equilibrium hexagonal phase, this unfavourable effect can be improved.