Al-Zn-Mg-Zr Alloy Containing Sc Homogenization And Hot Deformation Behavior

Novel Al-Zn-Mg-Zr alloy containing Sc has been developed by adding a small amount of scandium and zirconium on the base of medium-strength weldable Al-Zn-Mg-Zr alloy. The alloy has high strength, good corrosion resistance and welding performance, belonging to a new era of high-strength weldable structure material. Al-Zn-Mg-Zr alloy containing Sc can be applied in aerospace, nuclear energy and ship industry. Many investigations on the preparation and properties Al-Zn-Mg-Zr alloy containing Sc have been reported However, systematic studies on the deformation behavior and microstructural evolution of Al-Zn-Mg-Zr alloy containing Sc during hot compression have not been reported yet. There is lack of relevant theoretical basis for the actual hot-working processing parameters.The effects of homogenization treatment on the microstructure of Al-Zn-Mg-Zr alloy containing Sc were studied. And the homogenization process of the alloy was also optimized. The results showed that severe dendritic segregation existed in the ingot, and the alloy elements were unevenly distributed both inside the grains and along the grain boundaries. With increasing the homogenization temperature or prolonging the holding time, the residual phases dissolved into the matrix gradually and all elements became more homogenized. The proper homogenizing process was470℃/24h, which was consistent with the results of homogenization kinetic analysis.Isothermal compression tests of Al-Zn-Mg-Zr alloy containing Sc were performed on Gleeble-1500thermal simulator with the deformation range of60%, the deformation temperature range of340～500℃and the strain rate range of0.001～10s-1. The flow behavior of Al-Zn-Mg-Zr alloy containing Sc was studied by the true stress-true strain curve of the alloy. The results showed that the flow stress increased with increasing the strain rate or decreasing the deforming temperature, which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of150.25kJ/mol: ε=1.49×1010sinh(0.011σ)]7.50exp(-150250/RT). The microstructural evolution of Al-Zn-Mg-Zr alloy containing Sc during hot compression deformation was also studied by OM, SEM and TEM, respectively. The tendency of dynamic recrystallization enhanced with high deforming temperatures and low strain rates which corresponded to low Z values. With decreasing lnZ value lower than23.77, the main soften mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly, the subgrain size increased and the dislocation density decreased. According to the DMM processing map analysis, the suitable deformation condition for Al-Zn-Mg-Zr alloy containing Sc is400～440℃and0.001～0.3s-1.