The Influence of Quenching and Stretching Process Conditions of Aluminium Alloy Plates on Residual Stresses

The purpose of this article is to better understand the behaviour of the residual stresses in aluminium alloy plates, to control and minimize them by adjusting the quenching and the stretching process parameters. Residual stresses have usually the same role in a material as ordinary mechanical stresses, but while the stresses due to external loads can be calculated with a high degree of accuracy, the same thing cannot be said about residual stresses. The evolution of the residual stresses in the aluminium plates and the influence of the quenching and stretching process conditions was investigated by the Hole-Drilling method. The experiments were performed only on the industrial equipment. Plates with the same chemical composition were quenched by water spray or by immersion in water with or without agitation of the cooling medium. Also the plates quenched by water spray were unidirectional, bidirectional and successive stretchered. The results show the influence of the quenching conditions and of the stretching rate on residual stresses and also the correlation between the stretch rate and the residual stresses was established. Thus, the residual stresses increase from 158 MPa for quenched by water spraying to 187 MPa for horizontal quenched by immersion with agitation of the quenching water. The decrease of the residual stresses slope is reduced by the increase of the stretch rate with over 4%. The increase of the stretch rate with over 4% determines a significant reduction of the residual stresses.