onic microscope (TEM) and electron diffraction, etc. The test results indicated that obviously a diffusion transition zone forms near the interface of FeaAI/Q235 under the condition of heating temperature 1050～1100℃, holding time 60 rain and pressure 9.8MPa, which indicated that the diffusion interface of Fe3AI/Q235 was combined well. The diffusion transition zone consisted of Fe3AI and α-Fe(AI) solid solution. Microhardness near the diffusion transition zone was HM 480-540. There was not brittle phase of high hardness in the interface transition zone. This is favorable to enhance toughness of Fe3AI/Q235 diffusion joint.