PHASE–FIELD SIMULATION OF SOLUTE PRECIPITATIONS AROUND THE γ PHASE IN Al–Ag ALLOY

Abstract

Interactions between different precipitation products during phase decomposition for different alloys have been observed.Spinodal decomposition and intragranular precipitation are the two well-know mechanisms for explaining phase decomposition,both of which interaction mechanisms have been investigated experimentally in recently.A local free energy density function depending on aging temperature and composition has been proposed to describe the interaction between the Ag solute field andγprecipitates in phase-field simulation of spinodal decomposition in Al-Ag alloy.The evolution of spinodal decomposition in Al-Ag alloy with 4.2%Ag and 22%Ag has been simulated by the phase-field method using this function to represent numerically the precipitated Guinier-Preston zones(GPZ) around aγphase.The simulated results show that PFZ around a precipitated phase is an elliptical and its width is about two times the width ofγphase.In the region far from PFZ,a pattern of Ag solute field appears due to spinodal decomposition.When Ag-depleted zones are relatively far apart with each other,spinodal decomposition is strongly affected by them.The formation of PFZ resulting from spinodal decomposition has been initiated in the central region of the supersaturatedαmatrix before the modulation effect of Ag solute field at edge reachs here.It is found that two or three Ag-rich bands appear around the PFZ.During aging,Ag diffuses from not only theαmatrix but also the edge of Ag-depleted zones,where an accumulation of Ag occurs.After long time aging,many droplet-like Ag solute bands are formed near PFZ aroundγphase.These simulated results are in better agreement with the experimental results.