Abstract: To address the issue of cracking and failure in marine steel-aluminum explosive welding transition joints-caused by the growth and thickening of brittle intermetallic compounds (IMCs) at the interface during subsequent welding thermal cycles-industrial pure titanium (TA1) was selected as an intermediate layer for the steel-aluminum transition joint. Isothermal heat treatment experiments were conducted over a temperature range of 100~550 °C to systematically investigate the effects of temperature and holding time on interfacial microstructure evolution, IMC growth behavior, and mechanical properties. Results show that, at temperatures between 100 °C and 450 °C, only slight atomic diffusion occurred at the Al-Ti interface, with no continuous IMC formation observed. However, after prolonged heating (≥60 min) at 450~550 °C, a single, stable TiAl₃ phase formed at the interface; the IMC layer thickness increased gradually with both increasing temperature and holding time, accompanied by localized microcrack initiation-though full-interface penetration failure did not occur. The mechanical performance of the joint evolved in distinct stages, with 450 °C serving as a critical transformation temperature. By enabling the formation of a single-phase, slow-growing TiAl₃ layer at the interface, the titanium intermediate layer significantly enhances the high-temperature thermal stability and structural reliability of the joint, thereby providing theoretical support for optimizing heat treatment protocols.