Residual stress distribution in stress-relieved high-strength aluminum alloys

To date, 7075 is one of the most commonly used aluminum alloys in aviation. Due to its excellent combination of high strength, ductility and fatigue resistance, it is widely applied in highly stressed aircraft parts and was a precursor for lightweight aircrafts with reduced emissions. The mechanical properties of 7075 are highly dependent on its temper. In the overaged temper T7351, the residual stress that occurs due to quenching is relieved by a subsequent stretching process. In this paper we present an investigation regarding residual stress in a stress-relieved plate. We analyze in detail the residual stress distribution over the thickness in longitudinal and transverse direction by means of the layer removal test. The investigation results are in good agreement with theoretical considerations about residual stress in high-strength aluminum alloys. However, it also shows the limits of the layer removal test and the difference between measured distortion and the calculated residual stress. In addition, the investigation enabled a practical adjustment of the plate production to reduce residual stress according to the parts produced by a customer.