Quantified microstructural evolutions under uniaxial and plane strain loading states during hot deformation of 2219 aluminium alloy

Deformation route is one of the key factors that affects the microstructure evolution and hence the plastic flow behaviour during hot deformation. However, relevant research, which could quantitatively compare the microstructure distribution under different deformation routes, remains unknown. This work sheds light on understanding the microstructure evolution under uniaxial and plane strain tension with controlled deformation temperatures 350-535 °C and strains from 0.15 to fracture. Comparing dominating microstructural parameters, i.e. Geometrically Necessary Dislocation (GND), Low-Angle Grain Boundary (LAGB) and High-Angle Grain Boundary (HAGB), etc. Digital Image Correlation (DIC) was applied to characterise strain distributions and Electron Back Scatter Diffraction (EBSD) was applied to characterise and quantify the key microstructural parameters. Results show similar trends about the evolution of GNDs and HAGBs during deformation from a strain of 0 to 0.15 under uniaxial and plane strain tension, the GND density significantly increased by ∼319.7% and discontinuous HAGBs were progressed by ∼71.2% with increasing strain. Comparing to that under identical conditions in uniaxial tension, where the average generation of LAGBs and HAGBs under plane strain tension are 2-3 times lower. This is attributed to that fewer slip systems are activated and the dislocation multiplication rate is lower under plane strain tension. Apparent discontinuous HAGBs were created in uniaxial tension than that under plane strain tension condition, indicating that the dominant mechanism in uniaxial tension may be Continuous Dynamic Recrystallisation (CDRX), while co-occurrence of CRDX, Discontinuous Dynamic Recrystallisation (DDRX) and Geometric Dynamic Recrystallisation (GDRX) is present under both conditions. The increased temperature leads to the weakening of the uniaxial tension CDRX mechanism, while the plane strain is enhanced. The increase in strain promotes the occurrence of CDRX in both deformation routes. Furthermore, the lower fracture strain under plane strain tension may be attributed to the formation of damage. This work provides quantitative evaluations of process parameters on microstructure evolution compared with uniaxial and plane strain tension, constructing a foundation for future constitutive models and aiding manufacturing applications.