Reduction and Determination of Residual Stresses in 7xxx Aluminium Thick Plates

Residual stresses play an important role in the producibility of complex structural parts especially in the aerospace industry. Distortion due to residual stresses causes cost-intensive reworking and adaption of the milling procedure or even rejects. These adaptions are time-consuming due to lower milling speed, additional process loops, and increasing quality inspections. Thus, the semi-finished aluminum product industry aims to allocate plates free of residual stresses.

To achieve this stress-free quality, the last year's research has revealed that the amount of residual stresses depends on the homogeneity of the microstructure and texture in all spatial directions. Only this achievement allows stress reduction via stretching, as indicated in the literature.

Besides producing the homogenous microstructure, verifying the stress-free state is one of the major challenges. A non-destructive approach using ultrasonic runtime measurements can reveal the difference between the minimum and the maximum stress. This method's resolution is still not high enough to simulate the material's distortion caused by the milling procedure. For this reason, single-sided milling tests of complex, large parts are inevitable to emphasize the very high machining quality.