Predictions of residual stresses caused by quenching process in aluminium 6351-T6 gas cylinder.

Finite element (FE) studies were conducted to simulate quenching process in aluminium 6351-T6 gas cylinders. The simulations aimed to evaluate the effect of quenching process on the stress state of the cylinder including through thickness residual stress distributions. The gas cylinders are formed by a forging process whereby the open ended cylinder is forced into a forming die. The gas cylinders are then heat treated by using T6 heat treatment process to meet specifications for tensile strength and hardness. The forming and heat treatment processes introduce small folds and significant tensile residual stresses at the internal surface of the neck of the cylinder. When the effects of these folds and residual stresses arising from the quenching process are combined with the internal pressure of the cylinder, cracks may develop over time. The crack may result in the possibility of leakage or, more seriously, fracture of the cylinders. Previous experimental studies confirmed that high level of tensile residual stresses is present at the internal surface of the neck of the aluminium gas cylinders. Finite element simulations were conducted to model the temperature distribution and thermo-mechanical effects accompanying the quenching of aluminium gas cylinders from 530 degrees C to room temperature. Using FE to model the quenching processes, thermal inelastic deformation were studied and a residual stress distribution through the thickness of the neck of the cylinder were obtained.