Influence of interrupted quenching on microstructure and properties of 7xxx aluminium alloysWednesday (08.11.2017) 11:20 - 11:40 Part of:
7xxx-series aluminium alloys in different temper conditions (T6, T7x) are widely used for aircraft applications because of their superior strength, adequate toughness and acceptable corrosions resistance. In this study the influence of interrupted quenching (I.Q.) from solutionizing temperature (482 °C) to different temperatures (25–225 °C) on natural and subsequent artificial ageing was studied. Hardness measurements, tensile tests, instrumented impact tests and fracture toughness tests were used to characterize the mechanical properties. Additionally, the stress corrosion cracking behavior was investigated. Transmission electron microscopy (TEM) and atom probe tomography (APT) were conducted to characterize the microstructure evolution during I.Q. processing. The results show that a strength-level near T6-condition can be reached directly after I.Q. for a medium I.Q. temperature, without applying a common artificial ageing step. This corresponds to a similar density of strengthening precipitates produced already by I.Q.. Compared to standard water quenching, the hardening kinetics during a subsequent artificial ageing step 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. Moreover, the cluster-size distribution was found to be effected via I.Q. as well.