Method for fabricating superplastically formed/diffusion bonded aluminum

Abstract

A method for fabricating superplastically formed/diffusion bonded structures wherein metal blanks of aluminum or an aluminum alloy having an oxide surface layer are joined at selected areas by diffusion bonding and expanded superplastically to form a desired sandwich or integrally stiffened structure. According to such method, a suitable mask is applied to selected areas of the aluminum or aluminum alloy blanks. The assembly is then placed in a vacuum chamber and at a suitable low pressure and suitable voltage a glow discharge is created between the metal blank or blanks functioning as cathode or sputtering target, and an anode to selectively remove the oxide from the metal blanks and deposit the oxide debris on the anode. After the oxide layers have been removed from the surfaces of the blanks to be bonded, such surfaces are brought into intimate contact within the sputtering chamber or in an area equipped with heated platens, and while preventing reoxidation of the cleaned surface areas of the metal blanks, such blanks are subjected to press pressure and heat. The cleaned oxide-free areas bond, while the remaining areas, protected by the natural oxide and covered by the masks, do not bond. Such masks can be removed after sputtering and either prior to or during die bonding. If desired, the aluminum or aluminum alloy blanks can be initially anodized, to provide a thicker bond resistant oxide layer. The die bonded metal blanks are then subjected to superplastic forming in known manner to fabricate an integrally stiffened or sandwich structure.