Deformation behavior and failure mechanism of AA7075 alloy during the cryogenic temperature-assisted incremental sheet forming process
Yanle Li, Feifei Liu, Jiyu Du, Tingyu Ge, Vladimir V. Mironenko c, Fangyi Li
School of Mechanical Engineering, Shandong University
Journal：《Thin-Walled Structures》
Abstract：
High-strength aluminum alloys are potential structural materials for thin-walled aerospace and automotive components. However, the limited formability at room temperature (RT) hinders their wide industrial application. In this study, a cryogenic temperature-assisted incremental sheet forming (CT-ISF) process for manufacturing 3D curved thin-walled structures was proposed. An experimental platform for CT-ISF was established to form AA7075 alloys. We found that the formability of the solution-treated AA7075 alloy sheet was greatly improved under the cryogenic environment without sacrificing its strength. In combination with double pass forming process, the formability of the sheet can be further improved. The stable deformation of the sheet is promoted due to the suppression of the Portevin-Le Chatelier (PLC) effect at CT, which reduces axial force fluctuations during the forming process. The line roughness value of the meridional direction was reduced by 36.8% at CT due to the enhanced work-hardening and the utilization of MoS2 lubricant. In terms of microstructural evolution, we found that the fracture morphology of the formed parts changed from tensile fracture at RT to shear fracture at CT. The improved formability was attributed to increased Goss and E texture contents, delay in dislocation evolution, and suppression of the PLC effect. This work introduces a novel CT-ISF process that significantly enhances the formability of high-strength Al alloy. In particular, it unravels the enhancement mechanism of formability in the CT-ISF process, providing theoretical support for further research.
Keywords: Incremental sheet forming; Cryogenic temperature; Formability; Fracture morphology; Microstructure
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