EVOLUTION DURING DEFORMATION PROCESSING 5 6 X-Ray Tomography Study on Porosity and Particle Size 7 Distribution in In Situ Al-4 . 5 Cu-5 TiB 2 Semisolid Rolled 8 Composites 9 10

16 X-ray computed tomography (XCT) was used for three-dimensional (3D) 17 visualization of the internal microstructure and quantification of the porosity 18 and second-phase particles in Al-4.5Cu-5TiB2 composites prepared by an 19 in situ liquid metallurgy casting route. The as-cast composites were subjected 20 to hot rolling and mushy-state rolling for deagglomeration and to achieve a 21 uniform distribution of CuAl2-TiB2 particle clusters. Qualitative results ob22 tained by scanning electron microscopy (SEM) and quantitative results ob23 tained by XCT both showed that mushy-state rolling as well as hot rolling 24 resulted in fragmentation and a homogeneous distribution of the CuAl2-TiB2 25 particle clusters, with the mushy-state-rolled composite exhibiting the highest 26 number of smaller-size particles. The porosity was increased in both rolling 27 conditions through debonding of particles due to the compressive force during 28 solid-state deformation along with the quick solidification of the solute-rich 29 liquid during mushy-state rolling. These results show that application of 30 secondary processes such as hot-rolling and mushy-state rolling can help to 31 achieve a relatively more uniform particle distribution in Al-4.5Cu-5TiB2 32 in situ composites.