Diffusion bonding makes waves at Cambridge

A researcher at Cambridge University has developed a technique for diffusion bonding aluminium and aluminium base alloys to themselves and to other metals, leading to the filing of two patents.

The joining of such metals has long been a problem, because of the tenacious layer of surface oxide which is not always present. The difficulties become even more acute when the melting of the components to be joined is not an option. Dr Amir Shirzadi’s research has led to him being awarded the prestigious Henry Granjon prize from the International Institute of Welding.

He notes that diffusion bonding is an attractive technique for such troublesome metals because it is a solid state joining technique, which is normally carried out at a temperature much lower than the melting point of the material.

For joining aluminium alloys, the insertion of a thin copper or zinc interlayer allows a melting point eutectic phase to be formed at a temperature about100 degrees lower than the melting point. Even with this technique, the bond strengths produced are lower than the parent metal because of the planar bond interface which contains oxides and included particles. The new technique is based on imposing a temperature gradient across the surfaces to be joined to produce a non-planar interface which effectively increases the bonding area or metal to metal interface.This development means that it is now possible to change the shape of the interface from being planar to cellular, and up to fully dendritic depending on the temperature gradient imposed.

Shear test results on aluminium-based composites and alloys show shear strengths up to parent metal values. It is anticipated that this technique can be used for joining dissimilar metal combinations, metal matrix composites and possibly nickel based materials.