Abstract:
In this dissertation work, the processing-microstructure-property relations are examined for cold spray deposited AA2024 and AA7075. Unlike traditional thermal spray technologies, powders are never melted during the cold spray process. This approach allows for heat-sensitive materials such as 2000 and 7000 series aluminum alloys to be used for repair of components damaged by corrosion or fatigue. While a small body of literature for cold spray of AA7075 and AA2024 exists, further understanding on processing-microstructure relationships is needed and improvements to deposition characteristics, microstructure and mechanical properties are necessary for successful application. This dissertation examines four aspects of the cold spray process applied to AA2024 and AA7075. First the effects of processing parameters on process efficiency, deposit microstructure, and deposit properties of AA2024 and AA7075 are examined. Spraying with helium is found to be more cost effective than nitrogen or any mixture of nitrogen and helium and generally results in higher quality deposits. A novel heat treatment method is developed to solution heat treat gas-atomized AA2024 and AA7075 powders prior to deposition. This approach is found to significantly improve deposition efficiency of powders and homogenize the deposit microstructure by solutionization of segregated solute. The influence of the deposit geometry on the development of residual stresses are investigated for AA2024 and AA7075 using neutron diffraction. Generally compressive residual stresses are found in deposits and deposit geometry is found to significantly effect to magnitude of residual stresses evolved. Finally, the effects of heating the substrate/deposit using an in situ laser during deposition are assessed. Laser assisted cold spray is found to improve deposition efficiency and improving ductility of AA7075 deposits but can result in significant heat damage to the substrate material.
