Improving the Interparticle Bonding and Ductility of Cold Sprayed Aluminum Alloys by Deformation Processing

Abstract

Cold spray (CS) can produce thick coatings and free-standing bulk materials and is adaptable to additive manufacturing, including on-site repair. However, the structural applications of CS materials have been limited by the inherently incomplete interparticle metallurgical bonding in CS materials. In this work, an ultrasonic washing test (UWT) was used to semi-quantitatively assess the extent of interparticle bonding in CS Al6061 and CS Al2024 in relation to key CS parameters and post-CS deformation processing. Results indicate that spraying with a lighter gas or a softer powder promotes the interparticle bonding, although full metallurgical bonding is hardly achieved even by spraying at high deposition efficiencies. Sprayed particles remain in the deposit only because they acquire partial bonding that is sufficient to prevent them from bouncing off. Post-CS rolling and T6 heat treatment increase the interparticle bonding and hence ductility of CS Al alloys. Ultrasonic ironing (UI), a new post-CS deformation processing technique, also produces similar effects. The increased interparticle bonding by post-CS deformation processing arise from fragmentation of oxide layers inherited from powder particle surfaces and consequent metal-to-metal joining at the particle boundaries.