Hot-dip Aluminum Coating on Steel:Study on Diffusion Heat-treatment of Aluminized Steel
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We investigated the corrosion resistance of aluminized steel, which had been diffusion heat-treated at 700-1000°C for 1/4-2 hours in atmosphere, in the solutions with pH value of 1-14 range at room temperature and 60°C. At the same time, we studied the effect of diffusion heat-treatment on tensile strength and repeated bending value of the steel.The thickness of diffused alloy layer grows remarkably with substantial increase of diffusion rate when the base metal is heated above Ac3, 900°C. The diffusion layer has almost nothing to do with heating time.The aluminized steels diffusion heat-treated at 700-800°C have lower tensile strength than that of the steel as hot-dip aluminum coated, and it is less than 52kg/mm2. The aluminized steels diffusion heat-treated at the temperature above 900°C become to have higher tensile strength than that of the steel as hot-dip aluminum coated due to the remarkable growth of hard and brittle diffused alloy layer. On the contrary, the repeated bending value of these steels decreases rapidly by diffusion heat-treatment at the temperature above 900°C.The corrosion resistance of aluminized steel in acidic, neutral and alkaline solution with pH value of 1-14 range at room temperature and 60°C can be much more improved by diffusion heat-treatment at high temperature, however, the embrittlement of these steels by the growth of diffused alloy layer should be kept in mind.For example, the diffused alloy layer of aluminized steel heat-treated at 1000°C is only attacked less than 10% in the thickness after 6 weeks immersion in the acidic and alkaline solutions with pH value of all range at room temperature, especially less than 2% in the thickness in the nearly neutral solutions. This diffused alloy layer is only attacked respectively 19% and 23% in the thickness after 24 hours immersion in the solutions with pH 1.25 and 13.6 at 60°C.Even if the diffusion heat-treatment is performed at the temperature of less than 850°C, the diffused alloy layer has remarkably superior corrosion resistance in the acidic and alkaline solutions than metal and alloy layer of steel as hot-dip aluminum coated not only at room temperature but even at 60°C.
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社団法人 表面技術協会 | 論文
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