Recrystallized fine grains induced by nanoparticles in Al–Si–Mg–Cu-based alloy sheets

The effects of second-phase particles on recrystallization behavior were investigated for Al–Si–Mg–Cu based alloy sheets containing a small amount of Cr and Mn elements. Microscale (>1 μm) and nanoscale (<500 nm) particles were distributed in cold-rolled sheets. Particle-stimulated nucleation by microscale particles, such as Mg₂Si and β-AlFeSi, was not effective, while the α-Al(FeCrMn)Si nanoparticles (~5 nm) actively induced the formation of fine recrystallized grains. When the α-Al(FeCrMn)Si nanoparticles had a round-shaped and partially coherent interface with the Al matrix, they could act as heterogeneous nucleation sites for recrystallization grains. However, after homogenization heat treatment, the α-Al(FeCrMn)Si nanoparticles grew, decreased in number, and lost their coherency, which increased the recrystallized grain size. The sheet with a small grain size of 15 μm exhibited higher yield strength, ultimate tensile strength, and elongation than those of other sheets due to grain boundary and particle strengthening. In addition, the smallest-grain-sized sample was obtained when Mn or Cr content was 0.08 wt%, which is considered as a state in which nanoparticles can effectively participate in recrystallization nucleation.