As a key critical component of aerospace vehicles, high-temperature titanium alloy fuel tank frames have complex structures and significant variations in wall thickness, and this structural characteristic makes their fabrication via the precision casting process highly advantageous. To address the issue of the poor castability of ZTi55 high-temperature titanium alloys, the casting process was determined through a casting simulation conducted on the cylindrical structure of the fuel tank frame, and the relationship between the casting structure and the simulated temperature field was analysed. Furthermore, combined with the results of the casting dissection, the corresponding relationships between the simulated temperature field at different positions of the casting and the grain size were also analysed. The simulation results reveal

significant correlations between the cooling and solidification characteristics and the grain size at different positions during casting. Specifically, the curved thin-walled structure of the casting that is filled last undergoes cooling and solidification first and results in the finest grain size, at approximately 305 μm, whereas the thick-walled section filled first has the slowest cooling rate and features the coarsest grain size, exceeding 900 μm. Additionally, the wall thickness of the casting is significantly correlated with its solidification characteristics and grain size, where the greater the wall thickness is, the longer the solidification time required for the casting, the lower the cooling rate, and the coarser the grain size that ultimately forms.