Process-Microstructure-Property Relationships of High-Pressure Cold Spray Deposition of Aa7050 After in Situ Laser Heat Treatment

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University of Alabama Libraries

The objective of this research is to develop and characterize high-pressure cold sprayed AA7050 after in situ laser heat treatment. Successfully cold sprayed aluminum alloys with a low porosity promotes the idea to apply the cold spray technique from dimensional restoration to load-bearing structural repair. Recent literature shows that heat treatment of cold sprayed aluminum alloys ex situ in a furnace improved the mechanical properties, especially the elongation to failure. In this work, a laser source was used to in situ heat treat the cold sprayed deposit. Unlike the conventional furnace heat treatment of sectioned cold sprayed deposits, laser heat treatment brings the heat source to the deposits without removing the deposit from the substrates. The effect on the process-microstructure relation is studied from a precise control of laser heat input and characterization of grains and precipitates evolution in the cold sprayed deposit and substrates after in situ laser heat treatment. Low heat input from the laser evolved the microstructure in the deposit and did not decrease the hardness in the deposits and substrates. The process-microstructure-property relation in laser heated cold sprayed AA7050 is further studied with tensile tests and a systematical characterization of particle interior regions and particle boundary regions in the deposits. The elongation to failure in the laser heated deposit improved from 1.75% to 6.61%, attributed to the coarsening of the ultra-fine grains and precipitate. In addition, combination of experimental and simulation approach was used to examine the aging kinetics η' precipitates in wrought AA7050 after the T7451 temper. A significant decrease of precipitate density in post T7 heat treated AA7050 was revealed by scanning/transmission electron microscopy and Thermo-Calc/PRISMA simulation.

Electronic Thesis or Dissertation
AA7050, Cold spray, Laser, precipitate, TEM, Thermo-Calc/PRISMA