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A brief outline is presented of the factors involved in the search for gas-generating agents offering superior performance for foaming of liquid aluminium alloys. These include kinetic and thermodynamic characteristics of decomposition reactions, the ease of dispersion of the powdered foaming agent in the melt, the nature and likely effect of decomposition products on melt flow, potential reactions between the foaming gas and the melt and the availability, cost and ease of handling of the powder concerned. There is one very promising candidate material, calcium carbonate, which offers advantages compared to currently-employed hydride powders in virtually all aspects of their performance. It is shown that foams can be produced having appreciably finer cells ( |
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