Improved microstructures and mechanical properties for 7085Al alloy subjected to slow quenching by aging treatment

Abstract

The precipitation behaviors and mechanical properties of the slowly-quenched 7085Al alloy subjected to various aging treatments were studied by multi-scale microstructural and mechanical properties characterization techniques. There were coarse quench-induced precipitates (QIPs) including η phases and lath-shaped S phases identified at grain boundaries and Al3Zr particle interfaces during the slow quenching process. Both precipitate free zone and precipitate rich zone were characterized in the slowly-quenched samples after various aging treatments. It was found that the average size of the age-induced precipitates (AIPs) after the double-step aging treatment (D3) was finer, and the number density of the AIPs was larger than those after the single-step aging treatment (S1). Meanwhile, the precipitate free zones around the coarse QIPs and at grain boundaries became narrower in the D3 sample. Critically, the heterogeneous nucleation of η′ phase on the lath-shaped S phase which was previously unreported has been characterized. The orientation relationship between the η’ phase and S phase was determined, and the detailed mechanism was discussed based on heterogeneous nucleation theory. Furthermore, the yield strength and ultimate tensile strength of the D3 sample increased by ∼94.4 MPa and ∼65.9 MPa over the S1 sample, respectively. Finally, the underlying mechanisms of such yield strength variations were discussed. The mixture rule was used to model this microstructure-mechanical property relationship quantitatively, in which the calculated results showed the good agreement with the measured results.