FE-simulation coupled with CFD analysis for prediction of residual stresses relieved by cryogenic heat treatment of Al6061 tube

Abstract

This study aims to predict the residual stress relieved by cryogenic heat treatment (CHT) of an Al6061 tube. Conventional CHT commonly consists of solid-solution heat treatment, uphill quenching, and artificial ageing. To produce a new residual stress that is opposite to the original in nature, the solid-solution heat-treated aluminum parts are usually immersed in LN2 during uphill quenching with conventional CHT, followed by rapid heating of the parts using boiling water or high-velocity steam. First of all, conventional T6 and CHT experiments are conducted to measure the temperature of a tube with dimensions O200 mm × h200 mm × t10 mm. Computational fluid dynamics (CFD) analysis is conducted to calculate the convective heat transfer coefficient and temperature of the tube. These results are compared with the temperature in the experiment, and the comparison results are used to predict residual stress by means of FE-simulation. In particular, the relaxation of residual stress during artificial ageing is investigated using the Zener-Wert-Avrami function with the user subroutine. The predicted values of residual stress are compared favorably with the experimental results within a deviation of 10–15%, in contrast to measurements obtained by micro-indentation and saw-cutting tests. In addition, the experimental results show that conventional CHT can relieve as much as 57% of the residual stress induced by the water quenching of conventional T6 heat treatment.