Cold Spray of High Strength Aluminum High Entropy and Al 6061 Composite Coatings

Commercial aluminum (Al) alloys are restrained by the maximum strength achievable from their polycrystalline structure, limiting their performance in load-bearing applications. To circumvent this problem, a novel Al high entropy (Al HEA) composition is employed that utilizes the inherent strength from disordered atomic structure coupled with the ductility of polycrystalline Al6061. Two cold spray deposits are produced, the first being a pure Al HEA and the second Al HEA mixed with Al6061 in a weight ratio of 1:1. Higher ductility of Al6061 enabled deposition of 5.0 mm thick composite deposit compared to 0.15 mm thin pure Al-HEA deposit. The microstructure of these deposits comprises three different splats: featureless amorphous Al-HEA, partially crystallized Al-HEA, and polycrystalline Al6061. The cumulative response of these splats resulted in a bulk hardness of 261 and 440 HV in the composite and pure Al HEA deposits, respectively. The tensile plasticity of the composite Al HEA deposit by indentation plastometry showed a yield strength and ultimate tensile strength of 480 and 520 MPa, which surpasses the tensile properties of existing high-strength cold spray deposits of Al 7075 by 25%. This study advances state-of-the-art cold spray deposition of high-strength and lightweight Al alloys.