Development of tubular transition joints of aluminium/stainless steel by deformation diffusion bonding

Joining of aluminium and aluminium alloys to stainless steel is frequently required in many low temperature and nuclear applications. The present study describes a relatively new method of bonding these materials by suitably combining the deformation bonding and solid state bonding techniques for joining tubular assemblies. The stainless steel and aluminium specimens have been machined to form cylindrical tube specimens and special grooves have been machined on the inner diameter (ID) side of the stainless steel specimens. The polished stainless steel specimens have been coated with Ni, Cu and Ag in sequence on these grooves and Zn, Cu and Ag in sequence on the outer diameter side (OD) of the aluminium. The specimens have been bonded in hot vacuum press using argon as a pressurising medium and allowing the aluminium to plastically flow into the stainless steel grooves. Metallurgical investigation of the diffusion bonded specimen carried out at 315 degrees C for 4 h indicated excellent bonding and total absence of the intermetallic compounds in the reaction zone. The joints bonded at this temperature indicated that the bond strength was superior to that of the base material of aluminium and the bending angle was > 40 degrees. The paper presents the details of this technique and also methodology adopted for optimising the bonding parameters.