Formation mechanism and prediction model for peripheral coarse grain of high-strength aluminum alloy thermoplastic forming component: A case study on 2195 Al-Li alloy extrusion profile

Peripheral coarse grain defect often forms in high-strength aluminum alloy components, which pose great risks to service reliability and safety in aerospace applications. The prediction and suppression of this defect has become fundamental scientific challenges. To address this, this study takes the extrusion of 2195 Al-Li alloy as a case study to explore three key scientific issues: the formation mechanism of peripheral coarse grain, prediction models, and suppression strategies. It indicates that the formation of peripheral coarse grains primarily occurs in areas of plastic strain accumulation. As the plastic strain increases, a thicker layer of peripheral coarse grains is formed. The fundamental formation mechanism of peripheral coarse grain involves two primary steps. Initially, the accumulation of high plastic strain triggers dynamic recrystallization and grain refinement. Subsequently, during solid solution treatment, rapid grain boundary migration driven by large curvature leads to the coarsening of the fine grains. The prediction models for recrystallization and grain coarsening were established, which were embedded finite element software and successfully predicted the recrystallization driving force, recrystallization fraction, grain size, and grain coarsening rate in extrusion processing. Based on these findings, the strategies to suppress the peripheral coarse grain were proposed. This study fundamentally establishes a transferable framework that connects the thermoplastic forming process of high-strength aluminum alloys with the prediction and control of peripheral coarse grains, which allows for more reasonable process optimization strategies. This generic approach thus offers predictive guidelines for optimizing the microstructure and properties of other highstrength aluminum alloys.