Understanding and Simulating High Strain Rate Deformation of Magnesium WE43 Plate Products

Abstract

Magnesium-Yttrium-Rare earth alloy WE43 is being investigated as a potential lightweight armour material due to its low density and good strength-to-weight ratio, with particular interest in its ballistic and blast resistant properties. This requires a better understanding of the high strain rate properties of WE43. WE43 was tested at quasi-static and high strain rate (using Split Hopkinson Pressure Bar) in a range of orientations, strain rate ranges, and material tempers. The effect of temper was evaluated by comparing material in the T4 (solution treated) and T6 (peak aged) conditions. A novel 8-day over-aged temper was also utilized to evaluate whether over-aging could confer benefit to high strain rate properties. Consistent with previous work, it was found the strain rate sensitivity of WE43 is low and there was no abrupt transition in deformation mode activity with increasing strain rate. A comparison of the high strain rate performance of the T4 and T6 tempers revealed a difference in flow stress consistent with the difference expected at quasi-static rates. Testing in the very over-aged temper gave the maximum recorded strength at high strain rate in one orientation. This was explained on the basis of texture sharpening during over-aging and suggests the anisotropy of magnesium could be exploited to provide maximum strengthening in the direction where it is needed most. Microstructural evolution after heat treatment and deformation tested was examined using a range of optical and electron microscopy characterisation techniques. It was demonstrated that the deformation modes operative at quasi-static rates also operate at high strain rates. In particular, no strong increase in the activity of twinning was noted as strain rate increased. The results have been interpreted with the help of models calibrated against the experimental data. The Visco-Plastic Self-Consistent (VPSC) crystal plasticity model was used to predict deformation activity and capture the plastic anisotropy of WE43, It was demonstrated that this model can be used to reduce the calibration required for empirical high strain rate flow-stress models (Johnson-Cook) to be fitted to all applicable orientations.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philip Prangnell (Supervisor) & Joseph Robson (Supervisor)