Precipitation hardening processes in an Al–0.4%Mg–1.3%Si–0.25%Fe aluminum alloy

Aluminum alloys containing Mg and Si as the major solutes are strengthened by precipitation of the metastable precursors of the equilibrium β (Mg2Si) phase in one or more sequences. There are several metastable particles that can form during ageing, but the strengthening potential of these particles relative to one another is not extensively studied. In this paper, the precipitation and hardening potential of different metastable precursors in an Al–0.4%Mg–1.3%Si–0.25%Fe (wt.%) alloy is studied with the help of differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and hardness measurements. It has been found that the hardness increase in a freshly solutionized alloy during natural ageing occurs primarily due to precipitation of clusters and zones, while peak hardness is achieved due to precipitation of β” particles. The particles formed following β” phase are not effective hardeners.