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

Abstract:

In order to improve the uniformity of microstructure and comprehensive mechanical properties of 7034 aluminum alloy, this paper carried out the optimization design of the severe plastic deformation process and solution and aging treatment based on the reciprocating extrusion, characterized the mechanical properties of the material, the size distribution of grain and secondary phase and the quantification of dislocation configuration evolution, established the relationship between plastic deformation and heat treatment and the microstructure and mechanical properties of 7034 aluminum alloy. The results show that, the average grain size is refined from 59μm to 9μm, and the standard deviation of the average grain size decreases from 3.05 to 0.8 after three passes reciprocating extrusion; 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 η" phase, and the dislocations pile-up becomes in sub-grain. The interaction between the two 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 747MPa and 4.3% respectively, which are better than the two-stage solution + two-stage aging system.

Key words:7034 aluminum alloy; reciprocating extrusion; microstructure; mechanical properties; MgZn₂ phase