Modelling of microstructure evolution in hot deformation

Abstract
This paper reviews various approaches to the modelling of microstructure evolution in hot deformation, for the purpose of predicting the flow stress during deformation or for predicting the subsequent annealing behaviour. Two contrasting approaches are discussed, and illustrated for the example of hot plane–strain compression testing of Al–Mg alloy. These approaches are (i) physically based state variable models, in which the microstructure and property evolution is modelled explicitly; and (ii) advanced statistical methods, for linking processing conditions empirically to properties, or to annealing rate and final microstructure. The state variable models illustrate some general features of microstructure modelling and the level of experimental work that goes with it. Of particular importance are the accuracy of the data used to calibrate or validate a model, the implications that this makes on the volume of data needed, and the viable level of detail in the model that can realistically be verified. Various sensitivity analyses will be used to illustrate the need for a balanced view of model and experiment if a credible predictive capability is to emerge. The statistical methods provide no physical insight, but, nonetheless, warrant further consideration for hot–deformation problems. They potentially provide a means to optimize time–consuming experimental work, and may provide useful predictive capabilities for industry rather sooner than can be expected from complex physically based modelling.