X-Ray Tomography Study on Porosity and Particle Size Distribution in In Situ Al-4.5Cu-5TiB₂ Semisolid Rolled Composites

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