Mechanical behavior and microstructural evolution during hot torsion deformation of AA2219 ManufacturingX Lab

Many industrial methods for metal forming and processing require enormous strains and elevated temperatures to accommodate the needed deformation. However, current methods of material modeling are lagging the needs of industry practice, prominently in high strain, strain rate, and temperature environments. The following study uses hot torsion experiments coupled with FEA and microstructural evidence to bridge the gap between the industrial needs for material modeling and current systems. Sponsored by the National Aeronautics and Space Administration, this study uses aluminum alloy AA2219-T87, a commonly used aerospace engineering material to better understand the material behavior undergone during the practice of Self Reacting Friction Stir Welding (SR-FSW). The shear-based, deformation driven solid state welding practice has many mechanical similarities to hot torsion testing, hence the use of hot torsion for microstructural replication and analysis.

The following denotes some major findings within the scope of this project.

 Hot torsion resulted in enormous strains as well as several cycles of recrystallization (denoted by peaks and valleys in the torque-torsion curves).

 Through examination of the FEA modeled hot torsion specimen, a Johnson-Cook plasticity model was developed that closely matched the resulted torque-torsion curves. After satisfying the calibrated Johnson-Cook plasticity parameters, FEA appropriated strain and stress values were obtained to develop further modeling capabilities such as grain size prediction and predicting the onset characteristics for dynamic recrystallization.

Using optical microscopy as well as EBSD, grains were analyzed for their sizes, likely method of recrystallization, and other dependent factors to develop models to predict grain sizes and recrystallization environments. The ability to accurately model the microstructural evolution of a material during its manufacturing process further allows industries to make better practice decisions as well as more informed choices. The use of FEA, optical microscopy, and coupled experimental specimens grants advanced capacity for manufacturers to have certainty in their products.

The project is supported by NASA ESI under the grant No. 80NSSC19K0216, Multiphysics Integrated Modeling of Self-Reacting Friction Stir Welding.