Quench Sensitivity in a Dispersoid-Containing Al-Mg-Si Alloy

The quench sensitivity of a 6000 series alloy with a high content of dispersoids was studied over a wide range of cooling rate and natural-aging (NA) time. Positron annihilation lifetime spectroscopy, differential scanning calorimetry, and transmission electron microscopy were used to characterize the clustering and precipitation reactions. The alloy showed significant quench sensitivity after short NA (2 and 30 minutes), but the quench sensitivity was lower after long NA (24 hours). The quench sensitivity after the long NA can be accounted for by the solute loss due to the formation of nonhardening β′ precipitates on the dispersoids during cooling from solution treatment. For short NA, however, quenched-in vacancies and modifications to the precipitation sequence also have substantial contributions to the quench sensitivity. The current study provides new insight into the quench sensitivity of 6000 series alloys that contain a high dispersoid density.