Aluminum alloy diffusion connection method without intermediate layer

The invention relates to an aluminum alloy diffusion connection method without an intermediate layer. The to-be-welded surfaces of an aluminum alloy each are coated with a layer of activation protective agent for diffusion connection in combination with a gradient pressurization method. The coating magnesium-containing activation protective agent is completely volatilized during the welding process, and the welding surface is free of residues. A gradient pressurization mode is adopted, magnesium vapor and lower prestress are utilized in the high-temperature interval to realize oxidation film crushing, the welding temperature is reduced, the welding pressure is improved, and the high-strength and high-precision direct diffusion connection of the aluminum alloy is realized by utilizing the deformation control advantage of the low-temperature interval. The aluminum alloy diffusion connection method solves the problems of low strength, serious welding deformation and the like of direct diffusion connection of the