The precipitation behavior of Mg and Si during storage at RT in Al-Mg-Si alloys
pre-aged at 90°C was studied using a tensile test and differential scanning calorimetry (DSC)
measurement. Specimens were solutionized at 530°C, water-quenched and then pre-aged for 2, 6
and 12 hours at 90°C during which small precipitates were formed. In the pre-aged alloy, the
strengthening rate at RT has two stages. In the initial stage, the yield strength increases slowly with
the aging time and in the final stage, it increases rapidly. In the initial stage, the strength in the
pre-aged alloy is smaller than that in the non pre-aged alloy, while in the final stage, the strength in
the pre-aged alloy is larger than that in the non pre-aged alloy. Furthermore, the period of the initial
stage is dependent on the pre-aging period at 90°C. The DSC curves of alloys in the initial stage do
not show the presence of clusters, while those in the final stage do. It seems that in the initial stage
Mg and Si atoms accumulate around the small precipitates that have been formed in pre-aging at
90°C while in the final stage, the clusters of these atoms are formed.
The Application of Differential Scanning Calorimetry to Investigate Precipitation Behavior in Nickel-Base Superalloys Under Continuous Cooling and Heating Conditions
