Mechanical behavior and texture evolution of WE43 magnesium-rare earth alloy in Split-Hopkinson Pressure Bar and Taylor Impact Cylinder Testing

摘要

Mechanical behavior and texture evolution of Mg rare-earth alloy WE43 is investigated for strain-rates 10(-3)/s to upwards of 10(5)/s for the two material conditions - as-cast (AC) and T6 age hardened, rolled plate (RT6). The high strain-rate behavior is tested using both Taylor cylinder impact tests (TC) and split Hopkinson pressure bar tests (SHB) and bulk textures are obtained using neutron diffraction. Unlike the quasi-static strained material, AC and RT6 SHB retained high hardening rates throughout the test, even up to 30% true strain. Moreover, the high strain-rate data revealed that the RT6 material has a much higher strength than the AC material, but similar hardening rates despite significantly different initial texture. The flow stress near yield increased up to 10% for RT6 and up to 30% for AC as the strain-rate increased six orders of magnitude from quasi-static rates 10(-3)/s to 10(3)/s. Neither material exhibited significant plastic anisotropy over the broad range of strain rates, despite the fact that the RT6 material had a moderately strong initial texture. In the TC tests, the geometric cross-sectional changes and texture along the cylinder from the cylindrical sample foot to head are measured and from the neutron diffraction texture analysis, upper-bound estimates of twin volume fraction are obtained as well as dislocation density from analyzing diffraction peak broadening. Recorded geometrical changes along several loading directions show that the material has deformed homogeneously under impact. Analysis of deformed textures indicates that {10 (1) over bar2} extension deformation twinning occurred in the RT6 condition over the range of strain rates, with an upper bound estimate of 40% twin volume fraction for approximately 0.10-0.25 true strain. The peak texture components after the impact have their c-axes closely aligned with the impact direction. These observations are presented and rationalized in the paper.