Integrated modelling of transitions in mechanical conditions during casting and heat treatment

Abstract

The mechanical material behaviour of a cast component changes significantly during casting and heat treatment. The big difference in temperature levels during the different process steps causes different deformation mechanisms to be active. The thermal gradients promote transient stresses that can lead to inelastic deformations, residual stresses and in some cases to defects in the final part. It is a big challenge to make a reasonable transition in the mechanical model, and hence material data, when modelling several different coupled process steps. It is important to use an integrated approach where the transition is included in the full load history of the part. When industrial examples are considered, the sequence of process steps typically also changes the thermal and mechanical boundary conditions significantly e.g. going from being mechanically constrained during casting to being supported point-wise during the heat treatment process. This change includes mapping of results and obtaining equilibrium in a new global system, where the further reaction forces from the supports must be handled with contact conditions to e.g. predict deformations due to gravity during solution heat treatment. The work presented in this paper is focused on modelling the mechanical fields, taking into account the changes in the mechanical material model at different temperature levels, and the transition in mechanical behaviour when the microstructure is changing during the different steps of the heat treatment process. The approach used is based on a unified model where creep effects are considered at high temperature and rate effects are included in general during cooling. Proposals are made to include cooling rate sensitivity, annealing and precipitation hardening via modification of mechanical properties in the different process steps.