Effect of Heat Treatment on the Al-Cu Feedstock Powders for Cold Spray Deposition

This paper examines the effects of heat treatment on the Al-Cu feedstock powders used for cold spray deposition. In particular, we relate improvement of the powder to changes in the spray characteristics and microstructure of cold-sprayed coatings. The inert-gas-atomized Al-Cu powders were solutionized at 535 °C for 2 hours using a rotary furnace, followed by a water quench. Heat treatment of the powders not only eliminated most of the cellular solidification structure generated by the gas atomization process but also resulted in significant grain growth in the powder particles. After solution treatment, the copper content in the α-aluminum matrix increased as expected. After heat treatment, the powders were immediately cold sprayed onto AA2024 substrates. Heat treatment of Al-Cu feedstock powders significantly increased the deposition efficiency for all compositions tested. For heat-treated powders, the deposition efficiency systematically decreased with the increasing copper content, while the coating hardness increased. The formation of GP zones or θ″/θ′ strengthening precipitates through natural aging was not generally observed in the powder particles, but θ″/θ′ precipitates were observed in some cases for the cold-sprayed material with higher copper content.