Thermo-mechanical Processing of Mg Alloys

     Interest is being shown in Mg due to its light weight and high potential strength. However, traditional mechanical processing is difficult due to Mg's limited slip systems and anisotropic material properties. A severe plastic deformation (SPD) method called Equal Channel Angular Extrusion (ECAE), shown here, has achieved good results with Mg at elevated temperatures.

                                                       
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Figure 1. Schematic of ECAE and final billet

     This project investigates the effects temperature, strain-rate, and processing route on the microstructural evolution of Mg and a commercial Mg alloy called AZ31 following ECAE processing. Electron backscatter diffraction is being used to characterize the resulting microstructures.

                                                      
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Figure 2. Data collected by EBSD: A. Inverse pole figure maps from pure Mg processed at 0.03 in/s. B. A pole figure of the same data

      Of particular interest in the thermo-mechanical processing of Mg is a recovery-like process called dynamic recrystallization (DRX). During DRX, new grains nucleate and grow, generally resulting in grains with fewer dislocations than the parent grains and a change in texture. DRX occurs readily in Mg at many of the temperatures and strain-rates used in ECAE and is a significant factor in the resultant mechanical properties, but the process and mechanisms involved are poorly understood. To remedy this, in-situ diffraction neutron experiments have been performed during ECAE to provide insight into orientation evolution and grain growth during DRX. The analysis of these results is ongoing.

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Figure 3. (Above) Schematic of the neutron diffraction experiment. (Below) Image of the ECAE die, backpressure fixture, and cartridge heaters in the load frame.