Modelling of microstructure evolution in hot forming using unified constitutive equations

In hot metal forming processes, materials deform viscoplastically and the microstructure of materials changes dynamically (during the forming deformation) and statically (in the interval of operations or after forming processes). Techniques are required to enable the microstructure of a formed part to be predicted. In this paper, various models, developed by material scientists, are reviewed. They are used to model individual physical parameters of microstructure, such as grain size evolution in static and dynamic conditions, dislocation density accumulation and recovery, recrystallisation, dissolving rate of precipitates. Techniques have been introduced to incorporate mechanism-based microstructure parameters into a viscoplastic flow model to form a set of unified viscoplastic constitutive equations, which are implemented into FE solvers, through user defined subroutines, to simulate microstructure evolution in hot forming processes. Three examples are detailed in this paper. They are modelling of grain growth in superplastic forming, modelling of microstructure evolution in hot rolling and dissolving of precipitates in solution heat treatment (SHT) and their effects on viscoplastic flow of an Al-alloy.