Interconnected-phase mullite-aluminum metal-ceramic composites were processed using the indirect fused-deposition process. In this process, controlled-porosity ceramic preforms were fabricated via the lost-mold process. The molds mere designed with computer aided design (CAD) software and fabricated using a fused-deposition modeling (FDM) technique. Porous ceramic preforms mere infiltrated with aluminum metal, via pressureless reactive metal infiltration, to form the mullite-aluminum composites. Both the macrostructures and the microstructures of the composites were controlled via CAD and FDM. During metal infiltration, the mullite phase transformed to alpha -alumina, and an alumina-aluminum composite formed. This paper describes the mullite-to-alumina phase transformation during reactive metal infiltration of the porous preforms, as a function of processing variables.