Quantitative analyses of dissolution and precipitation kinetics of θ-Al2Cu phase in an Al-6.2Si-2.9Cu alloy using electrical resistivity

The dissolution kinetics of the theta phase during solution treatment and isothermal precipitation kinetics during aging in an Al-6.2Si-2.9Cu alloy were quantitatively examined through electrical resistivity, hardness, and transmission electron microscopy (TEM). The electrical resistivity successfully predicted that pre-existing theta particles in the as-cast Al-Si-Cu alloy were fully dissolved after 4.5 h at 500 A degrees C, which was in a good agreement with that directly observed by TEM. The electrical resistivity immediately decreased during aging at 250 A degrees C due to the precipitation of theta' phase and was saturated within 2 h. A maximum hardness peak appeared in 1 h at 250 A degrees C due to the formation of a metastable theta' phase, and then gradually decreased due to the coarsening of the theta' phase as well as the annihilation of the theta aEuro(3) phase. The theta' phase was finally transformed to theta phase after 3.5 h at 250 A degrees C.