In the present study, direct diffusion welding of aluminum alloy 5A02 and stainless steel SUS304 has been carried out in vacuum in the welding time range of 35–110 minutes. The effect of welding time on the interfacial microstructure and tensile shear strength of the joint were investigated. The joint with tensile shear strength of 101.3 MPa was obtained under the condition of the welding time of 60 minutes. The results reveal that the reaction layer thickness increases with the increasing of welding time and that the reaction layer consists of Al₅Fe₂ and Al₁₃Fe₄ formed in the interface. The strength of the joint is related to the reaction layer thickness and the value of the joint strength reached maximum when the reaction layer thickness was approximately 0.8 µm.

Ti-Al diffusion couples, prepared by resistance spot welding, were annealed up to 112 h at 823, 848, and 873 K in ambient atmosphere. The interfacial microstructure was observed and analyzed using SEM and TEM. The growth characterization of intermetallic compound formed at the Ti/Al solid state interface was investigated. Only TiAl₃ phase was detected in the interfacial zone, and its growth was governed by reaction-controlled mechanism in the previous period and by diffusion-controlled mechanism in the latter period. The activation energies were 198,019 and 122,770 J/mol for reaction-controlled and diffusion-controlled mechanism, respectively.