In situ synchrotron tomographic quantification of granular and intragranular deformation during semi-solid compression of an equiaxed dendritic Al-Cu alloy

Semi-solid deformation mechanisms are important in a range of manufacturing and natural phenomena, which range from squeeze casting to magma flows. Using fast synchrotron X-ray tomography and a bespoke precision thermomechanical rig, we performed a four-dimensional (3-D plus time) quantitative investigation of the granular behaviour of equiaxed dendritic three-phase materials. This methodology produced new insights into the formation of damage during the isothermal semi-solid compression (similar to 30% liquid fraction) of an A1-15 wt.%Cu alloy at both a macroscopic and microscopic level. Grain rearrangements, such as translation and rotation, were observed and lead to local dilatancy. The resulting flow of Cu-rich intergranular liquid into the dilated interstices gave rise to a local increase in liquid fraction, followed by rapid void growth above a critical axial strain of -6.4%. The local normal and shear strain distributions were quantified using digital volume correlation, identifying dilatant shear bands. At a microstructural level, the individual grains were also seen to undergo intragranular deformation, leading to bending and fragmentation of dendrites as grains interlock. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd.