Evaluation of Forging Process Induced Residual Stress in Aluminum Die Forgings

Aircraft structural components are being produced from forgings with increasingly complex geometries in a wide range of aerospace alloys. The forging process involves a number of steps required to attain favorable material properties (e.g., heat treatment, rapid quench, cold work stress relieving, and artificial aging). These processing steps, however, also result in the introduction of bulk residual stress. Excessive bulk residual stresses can have negative consequences including: part distortion during machining and/or during service, reduced crack initiation life, increased crack growth rates, and an overall reduction in part life. This presentation will summarize recent work related to quantifying and accounting for residual stress in aluminum die forgings. Key residual stress engineering concepts will be described. Since the artifacts studied are associated with an aircraft supply chain (multiple parts and multiple lots), the results are relevant to the aerospace community. Overall, the results show that forging residual stress is a repeatable phenomenon with approximately 30 MPa part-to-part variation.