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Aluminum profile structures are extensively used in the transportation industry and pose a considerable challenge to single-sided spot joining technologies. The widely used Huck BOM® riveting process requires prefabricated holes and thus significantly increases cost and reduces efficiency. In this study, a novel single-sided friction riveting (SSFR) process with an internal-threaded semi-tubular rivet is proposed to realize a screwed-solid state hybrid joining of aluminum sheet to profile structure without prefabricated holes. The results show that the upper trapped metal is welded with the lower profile structure under the thermal-mechanical coupled action generated by rivet stirring. The internal thread could facilitate material filling into the rivet cavity and form a mechanical interlock, so as to realize the single-sided joining between the sheet and the profile without prefabricated holes. The one-stage SSFR process could form shear texture and promote continuous dynamic recrystallization, but lead to excessive material softening and internal cracking. A two-stage process including friction softening and screw tightening could better coordinate the effects of heat and force, thereby avoiding cracking and refining grains in the stirring zone. Finally, the tensile-shear and cross-tension peak loads were respectively improved by 9.0 % and 29.3 %, compared to the joints with one-stage process and non-structural rivet. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • An in-situ micro-forging is introduced into cold spray to improve the adhesion. • Vortex-like material intermixing is periodically formed along the interface. • More dispersed interfacial oxide scale leads to improved metallurgical bonding fraction. • Adhesion of cold sprayed Al deposit is improved from 47.9 MPa to 107.2 MPa. [ABSTRACT FROM AUTHOR]