Modelling stress reduction techniques of cold compression and stretching in wrought aluminium alloy products

Heat treatable aluminium alloy aerospace products undergo a rapid quench from the solution heat treatment temperature into water/organic quenchant/spray quenching system during processing. As a result of this rapid quenching operation, residual stresses of yield strength magnitude can develop, leaving the material in an unsuitable condition for further machining operations and for service. Rectilinear, open-die forgings are generally cold compressed after quenching to relieve residual stresses. The effect of friction during cold compression between the forging and the steel compression platens, increasing/decreasing the amount of cold compression plastic deformation, natural ageing prior to cold compression, cold compression direction (LT v L v ST) and applying cold compression in 'bites' on residual stress magnitudes is not generally available. Residual stress development during quenching is modelled using the finite element technique and the effect on the final residual stress magnitude of varying these process parameters is evaluated. The effect of stretching to relieve residual stresses and the effect on residual stress magnitudes of sectioning samples of the material is also analysed using the finite element technique. The models of each of the stress relieving techniques are compared both by observing stress magnitudes and by using the FE model to predict the results from a layer removal technique.