The origination of fluorescent displays in ZTA7 titanium alloy casting after long-term trial run was analyzed. The microstructure of castings after cutting was investigated by SEM

metallographic examination and hydrogen content test was carried out. The results indicate that the microcrack fractures are characterized by brittle cleavage without obvious oxidation and common defects

such as shrinkage and inclusion

in area of microcrack sources

and no abnormality occurs in the microcrack area.It can be inferred that there is absence of defect in casting

and possibility of microcrack cleavage caused by casting defect is excluded. In addition

cracks appear on the machine surface after fluorescent detection of untested castings in same batch

proving that residual stress leads to the microcracks.