Fast diffusion bonding technique for extrusion-based additive manufacturing of high-strength aluminium alloys

In aluminium and its alloys, the efficacy of diffusion bonding and extrusion-based additive manufacturing (AM) is greatly limited by the presence of aluminium oxide (Al2O3) on the surfaces to be bonded. In the present work, a novel fast diffusion bonding technique is introduced, in which the surfaces to be bonded are mechanically scraped using an abrasive file immediately before bonding to remove or break the surface Al2O3 layer and reduce surface roughness so that the holding time can be reduced. In the present work, the new fast diffusion bonding technique has been experimentally investigated by bonding similar half-dogbone specimens of aluminium alloys AA7075-T6 and AA6061 to determine the effects of the bonding temperature, bonding pressure and holding time on the strength and properties of the resulting bonded specimens. Bonding curves, showing the pressure required for successful bonding as a function of temperature and holding time, have been constructed. Using the novel technique has been found to increase the maximum strength in tension of bonded specimens of AA7075-T6 and AA6061 by around 12% and 11%, respectively, compared with the conventional method. Metallographic examination has shown that the novel technique aids in eliminating residual microvoids from the bonding interfaces, providing further evidence that the new technique is effective in promoting good-quality bonding. The present work has demonstrated the feasibility of the novel diffusion bonding technique and opens up the possibility for application of the technique in extrusion-based AM to give a hybrid-AM process, allowing high-quality bonding between successively printed layers.