Hot tensile deformation behavior and microstructure evolution of 7075 aluminum alloy sheet

Abstract

The hot tensile deformation behavior of 7075 aluminum alloy sheet was studied using Gleeble-3800 thermal simulation machine at deformation temperatures of 400–475 °C and strain rates of 0.001∼1s−1. Microstructure evolution and fracture morphology were observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hyperbolic sine model is used to establish the constitutive equation of the relationship between peak stress and Z parameter. The results show that the hyperbolic sine Arrhenius constitutive equation can well characterize the flow behavior of the studied alloy, and the hot deformation activation energy is 132.52 kJ/mol. The average relative error between the predicted and experimental values is only 4.58%, and r2 is as high as 0.988, indicating that there is good consistency between the experimental value and the predicted value. When the strain rate keeps unchanged, the elongation of the studied alloy shows an upward trend in the lower deformation temperature range (400–425 °C). When the deformation temperature continued to rise to 475 °C, the elongation of the studied alloy decreased sharply. Based on the analysis of fracture morphology, a large number of dimples can be observed at 450 °C/0.001s−1, which is a typical ductile fracture. With increasing of deformation temperatures, the fracture mechanism gradually changes from ductile fracture to brittle fracture. Under the condition of 425 °C/0.01s−1, there are a lot of dislocations in the alloy, and the dislocation walls are formed. With the increase of deformation temperatures or the decrease of strain rates, the dislocation density gradually decreases and dynamic recrystallization occurs. The softening mechanism of the studied alloy changes from dynamic recovery to dynamic recrystallization.