Improved fatigue crack growth resistance by retrogression and re-aging heat treatment in 7010 aluminum alloy

Abstract

Aircraft grade 7010 aluminum alloy was heat treated to two different conditions: (1) standard peak aging (T6) and (2) retrogression and re-aging (RRA). The microstructures of these alloys were characterized by using transmission electron microscope. Fatigue crack growth rate (FCGR) tests were conducted using standard compact tension specimens, following ASTM standards. Tests were conducted at various stress ratios, R ranging from 0.1 to 0.7. The RRA-treated alloy was observed to contain coarsened ?? (MgZn2) precipitates with higher inter-particle spacing when compared with T6-treated alloy. The grain boundary precipitates (GBPs) were also coarsened and discontinuous in RRA-treated alloy as compared with continuous GBPs in T6 condition. The FCGR was lower and ?Kth was higher in RRA-treated alloy compared with T6-treated alloy at all the stress ratios investigated. Improved fatigue crack growth resistance in RRA-treated alloy was correlated to the modified microstructure and enhanced crack closure levels. 2018 Wiley Publishing Ltd.