Study of the recrystallization process of AlMgSi alloys containing transition elements

The addition of small amounts of the transition elements such as Zr, Mn and Cr, which have a low solubility in the α-aluminium solid solution and thus form dispersoids, to AlMgSi alloys showed that these elements inhibit recrystallization when the alloys are pre-heated prior to deformation. The formation of coarse particles during casting is mainly due to the presence of Fe. This type of particles found, even, in solution treated samples. The particles, with a diameter exceeding 3 μm, accelerate the recrystallization as they provide good sites for nucleation of recrystallization. Precipitate free zones (PFZ's) developed around the coarse particles favour nucleation of recrystallization by subgrain growth. The presence of dispersoid particles is found to shift the recrystallization energy peak towards higher temperatures. Intermediate annealing before deformation allowed to achieve a high rate of deformation by cold rolling due to the removal of the solute from the matrix by the formation of the hardening phases. Optical and transmission electron microscopy, hardness measurements and differential scanning calorimetry (DSC) were used to study the kinetics of precipitation and recrystallization of the AlMgSi alloys.