Abstract: During the casting process, titanium alloy castings inevitably have internal defects such as slag inclusion, porosity and shrinkage cavity.After the defects were removed, TIG welding was used to repair them, forming the structure of welding and heat affected zone different from the base metal.The coupling samples and comparison samples were cut from the base metal, welding and heat affected zone of ZTC4 titanium alloy castings.The galvanic corrosion and full immersion corrosion tests were carried out in artificial seawater.The galvanic current, corrosion potential, weight loss and corrosion rate were measured, and the metallographic structure and surface oxide layer were detected.The results show that the microstructure and surface oxide layer thickness of base metal, welding and heat affected zone of ZTC4 titanium alloy casting are quite different, the corrosion potential is similar, the galvanic current is close to 0, the weight loss and corrosion rate are very small, and there is no obvious galvanic corrosion tendency between them, and it has good corrosion resistance.Surface roughness has no effects on the corrosion potential and corrosion rate.The surface oxide layer has strong passivation and self-healing ability, which can be quickly repaired after being damaged without obvious corrosion signs.