Investigation on microstructural evolution of spray formed Al-Zn-Mg-Cu alloy during hot extrusion processes and subsequent solution treatment

The microstructural evolution of spray formed Al-Zn-Mg-Cu alloy was investigated during the hot extrusion with the extrusion speed of 5-70 mm/min at 400 degrees C and 450 degrees C. Then, the extruded rods at different deformation conditions were subjected to solution treatment for 2 h at 350 degrees C and 2 h at 475 degrees C. The influence of temperature and extrusion speed on the recrystallization mechanism and abnormal grain growth (AGG) has been unveiled. The results show that continuous dynamic recrystallization (CDRX) is the primary dynamic recrystallization (DRX) mechanism at the surface of the extrusion rod, and the main texture components were Brass {110} < 112 > . The center region is primarily characterized by a fiber texture (<100 > and <111 >//ED) and a limited number of fine recrystallized grains, formed through geometric dynamic recrystallization (GDRX), are observed at the grain boundaries. Furthermore, a fine-grained layer has been discovered on the extrusion rod surface and the thickness is primarily influenced by the deformation temperature. As the deformation temperature and extrusion speed increase, the dissolution of second phase particles leads to a reduction in pinning resistance, resulting in ACG at the outermost layer of the extruded rod and gradually developing into the peripheral coarse grain (PCG). In addition, the mechanism of PCG formation is primarily influenced by the history of local deformation. Considering the thermal-mechanical process and the pinning effect of the spray formed material, the optimal extrusion parameters are recommended to be at 450 degrees C with an extrusion speed of 10 mm/ min.