Effect of the Thermal Modulus and Mould Type on the Grain Size of AlSi7Mg Alloy

Thermal analysis has been used for decades for melt control before casting aluminum alloys. However, obtaining a good grain refinement in a standard cup does not ensure that the grain refinement is correct in real parts which may solidify at very different cooling rates. For this study, the effect of cooling rate on AlSi7Mg alloy with different metal qualities in terms of grain refinement was tested. The correlation between grain sizes measured on the standard cup with those obtained in cylindrical test parts with various diameters cast in sand and metallic moulds has been investigated. It was found possible to set up a formula for the grain size of the cylindrical test parts in function of their modulus and of the grain refinement obtained on the standard thermal cups. Corrective actions can then be taken in order to improve the metallurgical quality before casting.