Effect of Multi-directional Forging on Defect Elimination and Microstructure of Al-Zn-Mg-Cu Alloy

Al-Zn-Mg-Cu alloys are widely used for high-end carrier components in the aerospace industry, however, the mechanical properties of the components are poor due to the influence of defects such as residual crystalline phases and grain boundary element segregation. Therefore, multi-directional forging（MDF） tests are performed on homogenized Al-Zn-Mg-Cu alloy billets at a deformation temperature of 435 °C and a deformation rate of 0.01 s-1.The effects of multi-directional forging pass on the grain morphology, residual crystalline phase distribution, and elemental segregation during the multi-directional forging process are investigated by scanning electron microscope（SEM）, energy dispersive spectroscopy（EDS）, and electron backscattered diffraction（EBSD） microscopic characterization. The results show that the number of forging passes has a large effect on the reduction of the residual crystalline phase of Al-Zn-Mg-Cu alloy after deformation. With the increase of forging passes, the number of residual crystallites in the alloy gradually decreases, and the problem of Cu elemental segregation is significantly improved. After multi-directional forging with different forging passes, the core region shows coarser grains in microstructure, but a large number of newly recrystallized grains existed around the large grains, and the grain boundaries of the newly recrystallized grains had typical different continuous dynamic recrystallization characteristics, and this dynamic recrystallization trend was more obvious with the increase of forging passes.