Aluminum coatings calorized

At temperatures up to 500°C, aluminum coatings may be used in the as-applied condition, but, for service at higher temperatures, a subsequent diffusion treatment is recommended for hot-dipped and sprayed coatings calorized coatings do not require a diffusion treatment. A coating thickness of 300 pm is recommended as the desirable minimum for high-temperature sarice. 

Articles are heated in a hydrogen atmosphere in contact with a mixture of aluminum oxide and 3% aluminum chloride. After removal from the mixture the articles are heated in the range 620-710°C for 48 h. The coating thickness is generally 0.025-0.75 mm. The calorized coating must not be deformed. 

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