Strengthening and Toughening Mechanisms of 7034 Aluminum Alloy Subjected to Thermo-mechanical Treatment Based on Reciprocating Extrusion

In order to improve the microstructure uniformity and comprehensive mechanical properties of 7034 aluminum alloy, the optimization design of the severe plastic deformation process and solution and aging treatment based on the reciprocating extrusion was carried out. The mechanical properties of the material, the size distribution of grains and secondary phases and the quantification of dislocation configuration evolution were characterized, and the relationship of plastic deformation and heat treatment with the microstructure and mechanical properties of 7034 aluminum alloy were established. The results show that the average grain size is refined from 59 mu m to 7.4 mu m, and the standard deviation of the average grain size decreases from 3.05 to 0.8 after three passes reciprocating extrusion. After solution and aging treatment, the precipitation strengthening effect is better than the fine-grain strengthening effect, resulting in the reduction of elongation from 15% to 4%. Compared with the two-stage solution and aging treatment, the MgZn2 phase after single-stage solution and aging treatment is smaller in size, higher in density, and mostly semi-coherent eta' phase, and the dislocation pile-up evolves into sub-grains. The interaction between them is stronger and the strengthening effect is better. The optimal heat treatment system is single-stage solution+single-stage aging; under this condition, the tensile strength and elongation reach 747 MPa and 4.3%, respectively, which are better than those under the two-stage solution+two-stage aging system.