Improving the adhesion of cold sprayed Al deposits through in-situ micro-forging

The much lower processing temperature makes cold spray have many merits to deposit metallic coatings, repair failed metallic parts and additively manufacture metallic parts as compared with the high-energy beam based metal depositing processes. Although adhesion is critical for coating and repairing applications for cold sprayed deposits, it is still challenging to get high bonding strength especially for depositing materials with low density and elastic modulus. Here we introduced an in-situ micro-forging (MF) effect to cold spray by mixing 200–300 µm big-sized 410 stainless steel shot peening particles into the depositing Al powder. Due to the in-situ forging by the shot peening particles with 100 time higher kinetic energy than the depositing Al particle, vortex-like material intermixing between the Al deposit and the AZ31BMg substrate is periodically formed along the deposit/substrate interface. Meanwhile, the greatly improved interfacial plastic deformation at the deposit/substrate interface remarkably promotes the breaking and segmentation of the native oxide scale on both the spraying particle surface and substrate surface which promotes metallurgical bonding formation across the deposit/substrate interface. Both the vortex-like material intermixing induced enhanced mechanical interlocking and the improved metallurgical bonding contribute to a higher adhesion. As a consequence, the adhesion of Al deposit increases from 47.9 MPa to 107.2 MPa.