Development of Diffusion Bonding Techniques for Al-Li base Alloy AA8090

Abstract

AA8090 superplastic sheet is now commercially available allowing the intrinsic low density of the alloy to be combined with the complexity of shape possible from superplastic forming routes. In order to take full advantage of this technology and produce lightweight expanded structures, a selective bonding technique is required which produces a joint with adequate room temperature strength and capable of withstanding the stresses associated with the superplastic forming operation. Such technology is established in the production of titanium alloy components but has been hampered in aluminium alloys due to the stability of the oxide layer always present on surfaces exposed to the atmosphere.

A variety of bonding techniques have been investigated including diffusion bonding, thin foil interlayer and roll clad zinc interlayer (transient liquid phase bonding) routes. Detailed metallographic data demonstrating bond line integrity is reported along with room temperature shear strengths and peel strengths measured at superplastic forming temperatures. It will be shown that diffusion bonding and solid state bonding with interlayers invariably produces oxide debris at the bond line which limits the strength of the bond. Successful bonds can be produced using transient liquid phase bonding, satisfying high and low temperature strength requirements, providing the correct combinations of boning technique and process parameters are used.