The authors have realized that solution treatment may be possible at a higher temperature than that by the conventional air furnace if a fluidized bed furnace is utilized. In this study, solution treatment temperatures close to binary or ternary eutectic temperatures were used for a JIS AC4CH cast aluminum alloy. Mechanical properties were tested with internal microstructures such as micro-pores and intermetallic compound particles then being correlated using high resolution computed tomography. It is clarified that the solution treatment at the ternary eutectic temperature brings the improvement of strength by about 15.7 % for a relatively short solution treatment time (typically about 1/10 of the conventional condition by an air furnace) . On the other hand, the solution treatment at the binary eutectic temperature causes significant degradation by coalescence of micro-pores forming crack-like pores. These behaviors can be assessed by visualizing internal microstructures using the high resolution computer tomography (hereafter, CT). Overall, the combination of the superior heating furnace with the state-of-the-art temperature control and sophisticated visualization technique may enable the improvement of mechanical properties in aluminum cast alloys.