Age-hardening behavior of cast Al–Si base alloy

Abstract

In this paper, age-hardening behavior of cast Al–Si base alloys was investigated. It is found that double aging peaks are present in the age-hardening curves of Al–Si–Cu–Mg alloys and the first peak is higher than the second one when aged at temperature above a certain temperature, whereas a hardness plateau and single hardness peak are present in age-hardening curves of Al–Si–Mg and Al–Si–Cu alloys. The results of differential scanning calorimetry (DSC) analyses and TEM observation reveal that the age-hardening behavior is related to the precipitation sequence of alloys. For the Al–Si–Cu–Mg alloy, the first aging peak is the result from the high-density GP zone (especially GP II zones), while the second one is from metastable phases. Obvious interval during the transition from GP zones to metastable phases in DSC curve, which caused by dissolution of GP zones and the nucleation of metastable phases on dislocation, may be the main reason of the formation of double aging peaks. The aging plateau of Al–Si–Mg alloys is corresponding to the continuous transition from GP zones to metastable phases, while single aging peak of Al–Si–Cu alloys is caused by metastable phases.