Effect of heating rate during solution treatment on microstructure, mechanical property and corrosion resistance of high-strength AA 7075 alloy

Abstract

The heating rate during solution treatment exerted great influence on the final grain structure of AA 7075 alloy processed by thermo-mechanical treatment (TMT). In case of rapid heating rate, particle-stimulated nucleation (PSN) of recrystallization occurred and fine equi-axed structure with an average grain size of ~9 μm was obtained. On the contrary, when a slow heating rate was adopted, the resulting recrystallized grains were rather coarse and elongated (average grain length > 100 μm). After peak-ageing treatment, the mechanical property and corrosion resistance of 7075 sheets were closely associated with those grain structures. Specifically, two kinds of sheets exhibited equivalent strength while the ductility of fine-grained sample is considerably increased to 18.5%, 49% higher than that (12.4%) of coarse-grained sheet. Meanwhile, inter-granular corrosion (IGC) and exfoliation corrosion (EXCO) tests certify that the fine-grained sheet exhibited significantly enhanced corrosion resistance. Effective grain refinement induced by rapid solution treatment accounts for the notable increment in both ductility and corrosion resistance. Our results demonstrate that the comprehensive properties of 7000 alloys might be tailored by adopting proper heating rate when the alloys are subjected to solution treatment.