Abstract:The optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, hardness and electric conductivity measurements are employed to study the effect of deformation rate on the microstructure evolution and quench sensitivity of 7050 aluminum alloy. The results show that, the recrystallized fraction is very low with deformation rate at low level of 5 s⁻¹ and 8 s⁻¹. There are a large number of sub-structures in the samples and the average size of the sub-grains is quite small. The sub-grain boundary is hard to distinguish, which is called small-angle grain boundary, and a few equilibrium η phases mainly precipitates at these boundaries during air quenching after solution. With increasing the deformation rate, the sub-grains coarsen and the gradual boundary misorientation occurs, and more equilibrium η phase precipitates at the sub-grain boundary. Rolling at high deformation rate (15 s⁻¹) can increase the recrystallized fraction seriously. The equilibrium phases precipitate at the high angle grain boundaries and inside the recrysatllized grains with high density. Meanwhile, some precipitates are also observed inside the sub-grains. Actually, the incoherent Al₃Zr particles play a vital role in the precipitation of equilibrium η phase during air quench. The results of hardness and electric conductivity tests indicate that, with increasing the rolling rate, the loss of mechanical properties subject to the slow quenched samples increases, and the quench sensitivity of the alloy increases.

Key words: 7050 aluminum alloy; deformation rate; quench sensitivity