Effect of Zr addition on hot deformation behavior and microstructural evolution of AA7150 aluminum alloy

The hot deformation behavior of homogenized AA7150 aluminum alloys containing different Zr contents (0-0.19 wt%) was studied in uniaxial compression tests conducted at various temperatures (300-450 °C) and strain rates (0.001-10 s−1). Microstructural evolution was investigated using an optical microscope, a field-emission gun scanning electron microscope, a transmission electron microscope and the electron backscattered diffraction technique. The results reveal no significant variation in the peak flow stress or activation energy between the 7150 base alloy and the alloy containing 0.04% Zr. With a further increase in the Zr content to 0.19%, the values of peak flow stress and activation energy increased significantly. The materials constants and activation energy for hot deformation were determined from the experimental compression data obtained for all alloys studied. The solved constitutive equations yielded good predictions of the peak flow stress over wide temperature and strain-rate ranges for 7150 alloys with different Zr contents. The dynamic recovery level of the materials was reduced after being alloyed with Zr, which was associated with a decrease in the mean misorientation angle of boundaries and a decrease in subgrain size. The addition of Zr promoted the retardation of dynamic recovery and the inhibition of dynamic recrystallization during hot deformation due to the pinning effect of Al3Zr dispersoids on dislocation motion and to restrained dynamic restoration.