Improving creep-aging behavior and mechanical properties of AA7150 alloy via pre-aging

Improving creep ageing behavior and mechanical properties of Al–Zn–Mg–Cu alloys via different pre-aging temperature, using the creep ageing test, room-temperature tensile test and transmission electron microscopy observation. A pre-aging temperature of 120 °C markedly improved the mechanical properties of the samples, including a tensile strength of 605.2 MPa, yield strength of 583.4 MPa, and elongation of 13.8 %. Pre-aging generated a "peak age region" during creep ageing, advantageous for extending the ageing time and enhancing creep strain without compromising strength. Detailed microstructure and mechanical performance characterizations were employed to discuss and unveil the strengthening mechanisms. The results additionally illustrated that pre-aging effectively reduces creep strain, as compared to the T4 sample, by minimizing vacancy concentration. Furthermore, pre-aging can manipulate lattice distortion and creep strain by facilitating atom diffusion, and a larger lattice with a pre-aging temperature of 100 °C results in higher creep strain. Moreover, elevating the pre-aging temperature (120 °C) reduces vacancy concentration, thereby inhibiting the phase transformation from η′ to η precipitates. This led to the attainment of a desirable microstructure consisting of η′ precipitate with high density and dispersed distribution, significantly enhancing the strength of the alloy. Hence, a new method is provided for the manufacture of large-scale panel component with excellent mechanical properties.