Abstract
Effect of casting condition, especially of cooling rates, on the microstructures and mechanical properties of the AC4CH aluminum casting alloy has been investigated and the following results were obtained. Clear effect of the cooling rate on the dendritic structures was observed and reasonable linear relation between log DAS (dendrite arm spacing) and log R (cooling rate) was ascertained. In case of copper mold application, higher cooling rate dependence was obtained for the growth of the dendrite as compared to that of iron mold. Increase of the cooling rate resulted in an effective refining of the eutectic silicon phase, while a weak influence was observed on the spheroidization coefficient of the eutectic silicon. Effect of the cooling rate on the tensile strength was remarkable under the conditions of under-aging and over-aging. Higher values of the absorbed energy in the Charpy impact fracture were obtained by applications of the copper mold. Increase of the cooling rate raised magnesium concentration in the matrix. Above all, higher magnesium concentrations were certainly obtained for the copper mold applications as compared to those of iron mold.
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