温間変形した7075アルミニウム合金の超塑性に及ぼす温度とひずみ速度の影響

抄録

Hot deformation of prior warm-worked 7075 aluminum alloy was studied by means of 2-step tensile tests at temperatures ranging from 673 to 798 K and at various strain rates from 10⁻⁵ s⁻¹ to 10⁻¹ s⁻¹. Deformation behavior and structural development change at a critical temperature T_c around 730 K. In the region below T_c, a power law relationship with n\simeq3.3 is established between strain rate and flow stress, which suggests the deformation is controlled by the dragging motion of dislocations. In the region over T_c, the strain rate dependence of flow stress changes clearly in three regions of strain rate, \dotε. Typical superplasticity taking place in the medium region of \dotε results from the evolution of fine gained structure based on continuous dynamic recrystallization. It is concluded that hot deformation of the warm-worked 7075 aluminum alloy is affected by the changes in microstructure with temperature and straining, and can be controlled by dislocation motion in grains in the region of high \dotε or by grain boundary sliding in the regions of medium and low \dotε.