Grain refinement in as-cast 7475 aluminum alloy under hot deformation

Grain refinement in an as-cast 0.16%Zr modified 7475 aluminum alloy was studied by means of compression at 490 °C and metallographic observations. The σ versus ε behavior shows a significant strain softening just after yielding and an apparent steady-state flow at strains of above 0.3. The structural changes are mainly characterized by development of deformation bands at an early stage of deformation (ε≤0.3), followed by new grain evolution during steady-state flow due to operation of grain boundary sliding (GBS). GBS can result in local lattice rotation and formation of deformation bands in the as-cast coarse grain interiors. The number and the misorientation angle of deformation bands increase with deformation, followed by evolution of new grains in high strain. It is concluded that grain refinement occurs by a deformation-induced continuous reaction; that is continuous dynamic recrystallization (CDRX). A key role of GBS and second phase dispersoids on CDRX is discussed in detail.