Effect of superheating on structure of some aluminum alloys
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The effect of increasing pouring temperatures was investigated on several aluminum alloys, which were frozen at various rates ranging from less than 0.01°C/s (furnace cooled) to more than 20°C/s (thin metal mold). It was found that the higher the superheat, the faster the solidification rate. Interdendritic spacing, size of primary and eutectic constituents and grain size decrease with the increasing solidification rate that results from increased superheating, in spite of the fact that the actual freezing time increases. Indications are that aluminum alloys contain a nucleant that acts at zero undercooking and that superheating up to 500°C above the freezing point reduced the size and possibly the number of nucleating particles, but does not eliminate them completely.
KeywordsAluminum Alloy Metallurgical Transaction Solidification Rate Freezing Time Interdendritic Spacing
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