Abstract
This study investigates the evolution of the core microstructure and corresponding changes in mechanical properties of backward-extruded 7A60 aluminum alloy tubes during the extrusion–solution–aging process and elucidates the underlying regulatory mechanisms. The results show that the deformed core microstructure exhibits high thermal stability. Solution treatment promotes static recovery via dislocation rearrangement and polygonization, leading to the formation of a preliminary subgrain network and only a slight increase in the recrystallization fraction to 8.67%. During subsequent aging, strong Zener pinning by nanoscale precipitates effectively stabilizes low-angle grain boundaries, maintaining the subgrain fraction at ∼80% over a wide heat-input range (Hollomon–Jaffe parameter, TP = 8.07–8.65). Quantitative strengthening calculations confirm that precipitation strengthening is the dominant strengthening mechanism (≥64.9%), fully compensating for recovery-induced softening. At TP = 8.65, the area fraction of coarse secondary phases reaches a minimum of 2.6%. The strong <101> texture and deformed fibrous microstructure generate a delamination-toughening effect similar to that observed in Al–Li alloys, alleviating stress concentration and enhancing crack deflection. As a result, the alloy achieves optimal properties, with a tensile strength of 672.8 MPa and an elongation of 14.3%. However, at TP = 8.92, although the yield strength reaches 628.1 MPa, the recrystallization fraction increases to 19.2%, and the coarse-phase area fraction rises to 4.6%, causing a transition to intergranular brittle fracture and a significant reduction in elongation to 8.6%. Considering the strength-toughness balance, a heat input of TP = 8.65 is recommended for backward-extruded 7A60 Al alloy tubes.
Get full access to this article
View all access options for this article.