Quench Sensitivity and Quench-Induced Precipitation in High Strength 7xxx Series Aluminum Alloys

Abstract

This paper investigates the quench sensitivity of some selected 7xxx series Al alloys based on a Jominy End Quench method. The precipitate microstructures as a function of cooling rate during quenching are also characterized by using transmission electron microscopy (TEM). The results indicated that quench sensitivity and therefore the mechanical properties inhomogeneity in large plates or forgings can be predicted more accurately by the simultaneous combination of hardness and electrical conductivity measurements based on Jominy end quench. The hardness drop and conductivity increase in the novel alloy following a low cooling rate are much reduced compared to AA7050 and 7B04 because of a lower sensitivity to quench-induced precipitation on dispersoids. The novel alloy exhibited the least quench sensitivity, and the 7B04 Al alloy was the most quench sensitive. If the 90% of the maximum hardness is defined as the depth of quenching, the depth of 7B04 Al alloy, AA7050 through Jominy end quenching is about 20 and 55 mm respectively. Meanwhile, the depth of greater than 150 mm is achievable in the novel alloy, and hence it can be recommended to fabricate large section plates or forgings without compromising properties in the center of the part after a slow cool.