Development of duplex deformation substructure during extrusion of a commercial Al-5Mg-0.8Mn alloy

The microstructural changes which occur during the extrusion of a commercial aluminium alloy (AA 5456) have been investigated at macroscopic, microscopic, and substructural magnifications. Light microscopy has established that the deformation zone is not fully established until a short time after the peak or breakthrough pressure has occurred and that thereafter cylinder wall/billet shear is important in determining deformation. Light microscopy also reveals that recrystallized grains are present both at original grain boundaries and within grains when the deformation is advanced. Electron microscopy reveals that those grains contain a substructure and are thus dynamically recrystallized grains. The bulk of the material continues to deform with dynamic recovery as the operative mechanism. The deformation is thus duplex with dynamic recrystallization considerably modifying the structure normally observed in aluminium alloys. It is concluded that this occurs primarily because of the high solute additions but is also affected by the second-phase particles present in the comercial alloy.