Effect of Interrupted Quenching on Al–Zn–Mg–Cu Alloys

Abstract

Al–Zn–Mg–Cu alloys are widely used in aged-hardened condition for aircraft applications because of their high strength, adequate fracture toughness, stress corrosion cracking resistance and good machinability. In this study the effect of interrupted quenching (I.Q.) from solution temperature to 25–225 °C on subsequent artificial ageing was studied. Hardness measurements, tensile tests and instrumented impact tests were used to characterize the mechanical properties of Al–Zn–Mg–Cu plates. The results indicate that a high hardness can be reached directly after I.Q. for medium I.Q. temperatures. Compared to standard water quenching, the results showed that hardening kinetics and the age hardening response during artificial ageing can be enhanced for I.Q. at medium artificial ageing temperatures, but are reduced at high temperatures. I.Q. at high temperatures affects subsequent artificial ageing via the formation of precipitates, which contribute less to hardening but consume a significant amount of solute.