M.R. Rokni

Microstructural Evolution of 6061 Aluminum Gas-Atomized Powder and High-Pressure Cold-Sprayed Deposition

Gas-atomized 6061 aluminum powder was used as feedstock for deposition using a high pressure cold-spraying process. The microstructures of the as-received powder and cold spray processed (CSP) ultrafine-grained (UFG) 6061 depositions were characterized by different electron microscopy techniques. It was found that there is segregation of solute elements at the particle grain boundaries, which is increased after cold spraying (CS). Various microstructural features were observed in both directions (parallel and perpendicular) of the CSP layer, including low-angle grain boundaries, clustered-small-cell walls, and dislocation tangle zones. The results also indicated that a combination of different recrystallization mechanisms (i.e., continuous and geometrical) may contribute to the formation of nano and UFG structures during CS.

Review of Relationship Between Particle Deformation, Coating Microstructure, and Properties in High-Pressure Cold Spray

In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impacting the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys, but also ceramics and composites. During processing, the particles undergo severe plastic deformation and create a more mechanical and less metallurgical bond with the underlying material. The deformation behavior of an individual particle depends on multiple material and process parameters that are classified into three major groups—powder characteristics, geometric parameters, and processing parameters, each with their own subcategories. Changing any of these parameters leads to evolution of a different microstructure and consequently changes the mechanical properties in the deposit. While cold spray technology has matured during the last decade, the process is inherently complex, and thus, the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties remain unclear. The purpose of this paper is to review the parameters that have been investigated up to now with an emphasis on the existent relationships between particle deformation behavior, microstructure, and mechanical properties of various cold spray deposits.

Annealing behaviour of 6061 aluminium deposited by high pressure cold spray

Abstract Aluminium 6061 deposited by high pressure cold spray was analysed using a transmission electron microscope (TEM) to characterise its microstructure and response to annealing to 450°C in the plane of the deposition and perpendicular to the deposited layers. The cold sprayed deposition was also analysed with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) analysis and differential scanning calorimeter (DSC). Segregation of the solute atoms (Mg and Si) at the grain boundaries during cold spraying was seen to play a crucial role in stabilising the deformation substructure until specific temperatures, and was found to have a significant effect on the annealing behaviour of the microstructure in the two different directions.

Dissimilar metal joining and structural repair of ZE41A-T5 cast magnesium by the cold spray (CS) process

ABSTRACT The ability to join aluminum to magnesium is important for many industries but is a challenge due to the formation of brittle intermetallic compounds (IMCs). This article presents a practical method to join and provide structural repair of cast ZE41A-T5 cast magnesium (Mg) by the cold spray (CS) process using 6061 Aluminum (Al). In this study, the CS process was used to deposit 6061 Al onto ZE41A-T5 Mg substrates, which were subjected to materials testing and characterization. Shear, hardness, and tensile testing were conducted to determine bond integrity at the dissimilar metal joint. Electron and optical microscopy were performed to analyze the interface and microstructure. A review of dissimilar metal joining techniques is provided for comparative purposes, and the unique bonding mechanisms of cold spray are discussed because of its relevance to the results obtained. Results showed that the cold spray process limited the formation of Mg2Al3 and Mg17Al12 intermetallic compounds and the bond strength of the dissimilar metal joints created by the cold spray process, had an ultimate tensile strength, hardness, and shear strength comparable to the weakest material being joined (Mg). This study serves to demonstrate the potential of the cold spray process to create high strength dissimilar joints and provide structural repair between Mg and Al.