Effects of Microalloying Elements (Cu, Ag) on Nanocluster Formation and Age-Hardening Behavior in Al-Mg-Si Alloys

Abstract

Two types of nanoclusters playing an important role in the age-hardening behavior of Al-Mg-Si alloys are detected through differential scanning calorimetry measurements in the Base, Cu-added, Ag-added and Cu-Ag added alloys. The formation of Cluster (2) during aging at 100 degrees C suppresses the formation of Cluster (1) during a subsequent natural aging resulting in an enhancement of the age-hardening behavior during a final aging at 170 degrees C. Furthermore, low additions of Cu and Ag clearly enhance the precipitation hardening, as demonstrated by the hardness measurements. Higher precipitate numbers in the pre-aged specimens as compared with the naturally-aged ones were confirmed using transmission electron microscopy (TEM). The effects of low Cu and Ag additions on the nanocluster formation during the low temperature aging and the age-hardening behavior during the multi-step aging are discussed based on the age-hardening phenomena.