Strain Mapping of Al-Mg Alloy with Multi-scale Grain Structure using Digital Image Correlation Method

Al-Mg alloy powder was mechanically milled in liquid N-2 (cryomilling) to produce thermally stable powder with nanocrystalline (NC) microstructure for the manufacture of high-strength alloys. A multi-scale microstructure was achieved by blending unmilled coarse-grained (CG) powder with cryomilled powder and subsequently consolidating. The final bulk alloy was comprised of ultra-fine grained (UFG) regions and discrete CG bands. Dynamic observations of tensile deformation of the alloy were recorded using a micro-straining module attached to a light microscope, and the displacements were measured by digital image correlation (DIC). Strain inhomogeneity between UFG regions and ductile CG bands was observed in the micro-strain (strain order of 10(-4)-10(-6)) range, and the strain behavior was interpreted in terms of dislocation plasticity. Special emphasis was given to the distinct displacements between adjoining regions during deformation.