A comparative analysis of residual stresses from friction stir processing of aluminum cast 380 and wrought 7075 alloy sheets: experimental characterization and modeling

Residual stresses are often overlooked in friction stir processing (FSP), but their significant impact on fatigue performance necessitates their consideration in optimizing processing parameters. The first step in this effort is understanding how process conditions influence residual stress distributions, especially across different alloys. This study focuses on determining and explaining the through-thickness residual stress variations and the effect of process temperature on the residual stress magnitude in wrought AA7075 and cast AA380.0 alloys. Additionally, for AA380.0, the impact of a second FSP pass was investigated. To achieve this, hole-drilling electronic speckle pattern interferometry (ESPI) and the thermal pseudo-mechanical (TPM) model within finite element analysis were employed to study the 3D distributions of in-plane residual stresses in processed samples under various conditions. A key finding was the varying impact of process temperatures on residual stress magnitudes. Higher process temperatures reduced stresses in AA380.0 but increased them in AA7075. Additionally, the through-thickness stress distributions differed between the two alloys. Further analysis revealed that yield stresses are crucial in explaining these phenomena and the effects of additional FSP passes. Further, this fundamental understanding will be vital in guiding the efforts to mitigate residual stresses and assess their impact on the performance of FSP aluminum alloys.. Authors: Balusu, Kranthi [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000312654194); Samanta, Avik [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Univ. of South Florida, Tampa, FL (United States)]; Shukla, Shivakant [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)]; Das, Hrishikesh [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)]; Upadhyay, Piyush [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)]. DOE Contract: AC05-76RL01830. Subjects: 36 MATERIALS SCIENCE; Aluminum alloys; Friction stir processing; High-pressure die-casting; Hole-drilling electronic speckle pattern interferometry (ESPI); Residual stresses