Modeling of Quench-Induced Residual Stresses in Aluminum 7050 – T7452 Forgings

7050 aluminum forgings are widely used in the aerospace industry due to their combination of light weight, high strength and high fracture toughness. They are usually solution treated and aged in order to obtain the required properties. However, high residual stress could be introduced during solution treatment, especially during the quenching process which can result in significant distortion issues. Even though the distortion can be alleviated by a straightening operation, the high residual stresses remain and could cause even more problems in the subsequent cutting or machining operations and when the parts are in service. In the present work, finite element analysis is performed to investigate appropriate heat treatment and stress-relieve practices for the reduction of residual stresses of a 7050 aluminum forging. Solution treatment heating and quenching, stress-relieving and ageing procedures are all included in the model. In order to provide increased accuracy for quenching simulation, heat transfer coefficients are input as functions of both temperature and locations. Comparisons are made between different immersion rates, part orientations, quenching delays, and different percentages of stress relief. The simulated residual stresses and distortion are then validated experimentally using hole-drilling methods and CMM dimensional measurements.