Microstructural and mechanical characteristics of hot worked homogenized AA7068 using 3D processing map and DEFORM-3D

Abstract

AA7068 is classified as high strength aluminum alloy and is primarily utilized in wrought conditions which can be achieved with hot deformation. The process of hot deformation is a competent way of optimizing material properties; thus, understanding its deformation behavior in the wide range (250–450 °C, 10−3–100 s−1) is vital in processing a high-performance product. The true stress-true strain trend indicated its dependence on thermomechanical variables and precipitate size. The constitutive calculations accurately predicted the flow stress behavior. The kinetic rate calculations demonstrated that glide dislocation motion (with a value of n = 6.3) was observed during hot deformation. 3-dimensional processing map (PM) has revealed a progressive rise in efficiency (η) with increase in true strain. The PM analysis has successfully identified both stable and unstable working regions. Within the stable working region, a peak efficiency (η) of 54% was observed in the range of 347–359 °C and 10−3 s−1, 0.69 true strain. In, the stable working region, the microstructural characteristics demonstrated a notable increase in the dynamic softening depending on the process time and deformation temperature. At lower temperatures, the dynamic softening in the deformed specimens predominantly occurred through dynamic recovery (DRV), whereas at high temperatures, it facilitated by dynamic recrystallization (DRX). The DRX during deformation was observed to occur through continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) mechanism. Hot forging finite element modeling (FEM) exhibited an uneven material flow with the peak effective strain occurring in the core of the specimen. Open forging in the optimum working conditions resulted in the highest tensile strength of 340 MPa, observed at a temperature of 450 °C and strain rate of 10−3 s−1.