Two experiments are conducted to study flow and heat transfer behavior in a molten metal droplet on a cold surface following impingement. Laser holographic interferometry is employed to visualize molten metal-solid contact state in real time over the entire solidification process by means of a high-speed video camera. The formation of two distinct solidified layers is disclosed. One, formed in the early stage of solidification, adheres to the cooling surface and is latent heat controlled. The other, formed in the later stage, is nonadhesive and radial-shaped, and is dominated by a slip flow of the molten phase accompanied by phase change. The latter is verified by a separate experiment using thermocouple measurements and inverse conduction theory. These two different heat transfer mechanisms may cause transient thermal and residual stress problems, which would affect the quality of solidified metal products. Results for solidification of a single molten metal drop on quartz and copper surfaces, representing two extremely different thermal conductivities, are compared.
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