Effect of Extrusion Ratio on Microstructure and Mechanical Properties of 7A85 Aluminum Alloy

The extrusion ratio strongly influences the deformation behavior and final properties of aluminum alloy extrusions. In this study, the effects of extrusion ratio (13, 16, 20, and 26) on the microstructure and mechanical properties of 7A85 aluminum alloy were investigated by tensile testing, hardness and electrical conductivity measurements, EBSD characterization, and DEFORM-3D finite element simulation. The results show that the sample with an extrusion ratio of 13 has the finest recrystallized grains (5.73 μm) and the highest average misorientation angle (26.25°), indicating a relatively high degree of recrystallization. In contrast, although the sample with an extrusion ratio of 20 exhibited a mixed grain structure (a mixture of fine and coarse grains) and incomplete recrystallization, it achieved the highest as-extruded tensile strength (502 MPa). The strength degradation of the sample with an extrusion ratio of 26 is due to excessive recovery and grain coarsening. After T6 heat treatment, the strength difference between samples with different extrusion ratios was basically eliminated (~690-697 MPa). Combined with the simulation results under different extrusion ratios, the temperature field and material flow field in the extrusion process were analyzed, and the deformation and recrystallization mechanisms were deeply understood. These results indicate that the intermediate extrusion ratio can provide the best balance for the as-extruded material's strength, and the T6 aging response is relatively insensitive to the extrusion ratio. However, fine and uniform recrystallized grains are more conducive to a stable aging response. This work provides guidance for optimizing the extrusion process parameters of 7A85 aluminum alloy.