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

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 (sigma(-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.