Quench Sensitivity of 7475 Aluminum Alloy Using End-Quenching Technique and TTP Diagrams

The quench sensitivity of 7475 aluminum alloy has been comprehensively investigated by hardness testing, electrical conductivity measurements, scanning electron microscopy, and transmission electron microscopy. Based on the end-quenching method and time–temperature–property (TTP) diagram, the key factors affecting the quenching of the studied alloy were identified and are discussed in comparison with other 7000 series alloys. The results indicate that 7475 alloy is relatively sensitive to cooling rate, with a critical temperature range between 300°C and 350°C. The nose temperature of the TTP curve is approximately 330°C, and the incubation period is 1.5 s. When the cooling rate is lower than 12.5°C/s, the density of Guinier–Preston zones and η′ precipitates decreases remarkably, and the width of the precipitate-free zone becomes wider. Simultaneously, coarse η phases precipitate at grain/subgrain boundaries and Al18Mg3Cr2 dispersoids. These quench-induced η phases consume numerous solute atoms and therefore suppress the formation of the strengthening precipitates, leading to a deterioration of the mechanical properties.