In-situ analysis of grain rotation and lattice strain within a magnesium polycrystal based on synchrotron polychromatic X-ray diffraction technique: (I) prior to twin

Abstract

Hexagonal-close-packed structure aggregates exhibit complicated deformation behaviors, involving different slips and twinning. Synchrotron polychromatic X-ray microdiffraction (micro-XRD) was utilized to study in situ an extruded Mg-3Al-1Zn strip subjected to uniaxial tension. The evolution of grain rotation and lattice strain was analyzed under the load levels from 12 to 73 MPa. The micro-XRD data was used to map an area of 396 × 200 μm within the region of interest. The experimental set-up and X-ray diffraction microscopy in two dimensions allow the morphology, orientation and strain of the target grain to be determined at the submicron size. Results depict local orientation fluctuation, lattice strain evolution, slips system and elastic modulus within the same grain. As the applied load increases, the grain's rotation is accelerated between 46 MPa and 51 MPa at which level of load the grain-scale plastic deformation is activated. The predominantly slip modes prior to twin are identified as the combination of b1→ = (0002) [112¯0] andb3→ = (0002) [2¯110]. During the inspection, all reflection planes displayed an onset of micro yielding at the macro load level of ∼38 MPa. In this work, we confirm that magnesium is nearly elastic isotropic.