Abstract: Microstructure evolution and strengthening and toughening mechanisms of 2024 aluminum alloy thin-walled tube subjected to indirect isothermal extrusion and after annealing treatment were studied by means of SEM and TEM characterization techniques. The results show that during the extrusion process, plastic deformation induces the precipitation of fine S(Al₂CuMg) phase along the extrusion direction, while the homogenized state T(Al₂₀Cu₂Mn₃) dispersed phase is retained, which plays a dual role of suppressing recrystallization and dispersion strengthening, and produces high-density dislocations and forms a subgrain structure. As a result, the tensile strength of the extruded alloy increases to 304.73 MPa, and the elongation after fracture reaches 12.3%. After the annealing treatment, the partial coarsening of the S phase weakens the precipitation strengthening effect. However, the dislocation entanglement network promotes the refinement of sub-grains and enhances the grain boundary pinning effect, further improving the plasticity (the elongation after fracture reaches 15.7%). At the same time, the orientation of the S phase weakens and tends to be equiaxed, reducing the anisotropy and resulting in a decrease in the strength of the alloy.

Key words: 2024 aluminum alloy, indirect isothermal extrusion, microstructure evolution, strength and toughness