Abstract
A combined grain boundary segregation and precipitation model is presented. The model predicts the formation of precipitate free zone (PFZ) at the grain boundaries in aluminium alloys, accounting for the quench rate after solution heat treatment and the following heat treatment during which hardening precipitates are formed. The diffusion of vacancies and solute elements towards the grain boundary is treated, including both non-equilibrium and equilibrium segregation as well as nucleation and growth of bulk and grain boundary precipitates.
The segregation of alloying elements, like Cu, to the grain boundary and formation of PFZ plays an important role for the susceptibility of Cu-containing 6xxx aluminium alloys for intergranular corrosion (IGC). Especially it seems important whether a continuous Cu-film is formed at the grain boundary. The width of PFZ is also important for the mechanical properties, because it provides a soft zone in which strain can be localised. Hence, in practical applications it is important to be able to control the solute segregation and the width of PFZ. The aim of this work is to provide a combined model that accounts for the main phenomena that occurs during the cooling from the solution heat treatment and the following heat treatment. The model can be used as input to evaluate how a given alloy composition and heat treatment will influence the susceptibility for IGC and mechanical behaviour.
The segregation of alloying elements, like Cu, to the grain boundary and formation of PFZ plays an important role for the susceptibility of Cu-containing 6xxx aluminium alloys for intergranular corrosion (IGC). Especially it seems important whether a continuous Cu-film is formed at the grain boundary. The width of PFZ is also important for the mechanical properties, because it provides a soft zone in which strain can be localised. Hence, in practical applications it is important to be able to control the solute segregation and the width of PFZ. The aim of this work is to provide a combined model that accounts for the main phenomena that occurs during the cooling from the solution heat treatment and the following heat treatment. The model can be used as input to evaluate how a given alloy composition and heat treatment will influence the susceptibility for IGC and mechanical behaviour.