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To produce a specific grain size in metallic coatings requires precise control of the time at temperature during the deposition process. Aluminum coatings are deposited using electron-beam evaporation onto heated substrate surfaces of both mica and lithium flouride. The grain size of the coating is determined upon examination of the microstructure in plan view and cross-section. Ideal grain growth is observed over the entire experimental range of temperature examined from 413 to 843 K. A transition in the activation energy for grain growth from 0.87 to 2.04 eV atom −1 is observed as the temperature increases from <526 K to >588 K. The transition is indicative of the dominant mechanism for grain growth shifting with increasing temperature from grain boundary to lattice diffusion.