Microstructures and properties of a high strength, toughness, and corrosion resistance Al-Zn-Mg-Cu alloy under an over-aging state

Abstract

• Highest fracture toughness and critical stress intensity factor in Al-Zn-Mg-Cu alloy. • The excellent mechanical properties were attributed to the novel heat treatment. • Deformed structures without recrystallization retained after aging. • Pre-aging treatment introduced G.P. zones, leading to fine age hardening precipitates. • The size of the GBPs and the width of PFZs were significantly reduced. This work studied an Al-Zn-Mg-Cu alloy with excellent comprehensive properties using a novel heat treatment. The result shows that the fracture toughness ( K IC ) value of 65.2 ± 2.0 MPa∙m 1/2 and critical stress intensity factor ( K ISCC ) of 37.9 ± 1.7 MPa∙m 1/2 can be achieved. Each of which is the highest value reported. The fatigue strength with this heat treatment exceeded 180 MPa at the stress ratio of −1 ( σ -1 ), which was much higher than the other Al-Zn-Mg-Cu alloys with similar tensile strength. This superior combination of mechanical properties and fracture toughness for the studied alloy is greatly attributed to a significant fraction of deformed grain structures and dense age hardening precipitates evolved from existing G.P. zones.