Influences of precipitation behavior on the microstructural evolution and mechanical properties in Al-22 at% Zn alloys

Al–Zn based alloys with high Zn content are limited in practical applications due to low ductility. Introducing discontinuous precipitation (DP) into the alloy offers a promising route to optimize the mechanical properties. This paper takes Al-22 at% Zn as a model alloy to study the precipitation behavior, delineating innovative strategies for the improvement of mechanical properties. Through appropriate treatment, the volume fraction of DP in this alloy can reach about 90 %. The DP microstructure of this alloy is composed of lamellar Al and Zn phase arranged in layers. As a precipitation mode competing with DP, continuous precipitation exists in this alloy in the form of granular Zn precipitates, with the precipitation-free zone (PFZ) located at the interface between these two precipitated structures. Electron Backscattered Diffraction results suggest that the introduction of DP into the alloy reduces local stress concentrations within the microregions, which could account for the observed increase in ductility with the increase in DP content. The presence of PFZ induces the accumulation of dislocations and exerts an adverse influence on the ductility of the alloy. Variations in the PFZ content serve as a significant factor contributing to changes in alloy strength.