Cold Sprayed Discontinuously Reinforced Aluminum (DRA)

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Abstract Discontinuously reinforced aluminum (DRA) has many attractive mechanical and physical properties. Discrete hard particles such as B4C have been added to aluminum alloys, such as 6061, to add strength and stiffness for an improved performance. Traditionally, these particles are introduced in melt additions and extruded or made into preforms and cast. These ceramic particles are also added in aluminum through a powder metallurgy process resulting in extrusion or forging. Inhomogeneous distribution of these particles in casting results in inferior properties and also it is difficult to produce preforms with high volume fraction materials. While wrought properties can be achieved in the powder metallurgy approach, extrusion directionality of the process introduces anisotropic properties. Though thermal spray has been used to produce DRA coatings, it has been observed that the melting and re-solidification of the aluminum matrix material as well as reaction with potential substrates such as copper is of concern. Since cold spray does not melt the feedstock material, it is ideally suitable for producing DRA coatings. Boron carbide particles and 6061 aluminum alloy were used as reinforcing and matrix material respectively. Experimental studies were carried out to optimize the raw material characteristics, DRA powder preparation technique and spray parameters, and using these optimized parameters, dense and strong coatings and free-forms were produced. Proper selection of the particle size distribution of the matrix and reinforcing materials, wet blending them and subsequent drying yielded the required spray feedstock. Optimization of the spray parameters resulted in strong, dense and well-bonded coatings with acceptable deposition efficiency and deposition rate values. Post spray heat treatments were carried out to retrieve the ductility of the specimens. A series of mechanical property measurements were carried out on the as-sprayed and heat treated specimens. Results of these studies were analyzed to evolve a preliminary model of the DRA structures and establish the feasibility of cold spray production of DRA coatings and free-form structures.