Correlative Differential Scanning Calorimetry and (Scanning) Transmission Electron Microscopy Study of the Influence of Interrupted Quenching and Natural Aging of a 6082 Alloy

Abstract In this work the effect of interrupted quenching and natural aging prior to artificial aging was analyzed on the early GP-zones and resulting precipitates in a 6082 alloy by differential scanning calorimetry (DSC) and (scanning) transmission electron microscopy ((S)TEM). DSC was used to “scan” along the precipitation path and find interesting temperatures which were subsequently analyzed by (S)TEM. It was found that natural aging prior to artificial aging results in “square GP-zones”, whereas directly aging without natural aging results in mainly “ β ′′-eye” GP-zones. Furthermore, it was shown that the square GP-zones facilitate the precipitate growth, since significantly wider and longer precipitates arise from microstructures with square GP-zones. On the contrary, “ β ′′-eye” GP-zones result in many but significantly smaller precipitates. A suggested atomistic model of the square GP-zones which builds around a vacancy is suggested. Simulations of this model result in the same contrast variations in low-angle annular dark-field STEM as observed experimentally. Lastly, it was found that reducing the vacancy concentration by interrupted quenching from the solution heat treatment temperature limits the coarsening effect of the square GP-zones on the final precipitates.