Thermal analysis as a microstructure prediction tool for A356 aluminium parts solidified under various cooling conditions

Thermal analysis performed with standard cups has been used since decades for melt control and microstructure prediction before casting aluminium alloys. However, obtaining a proper microstructure in a standard cup does not ensure that the microstructure is correct in real parts which may solidify at very different cooling rates. For this study, A356 alloy with different metal quality in terms of modification and grain refinement was tested. Different cooling rates were obtained by employing cylindrical test samples with various diameters cast in sand and metallic moulds. The correlation between microstructure features such as grain size, modification rate and secondary dendrite arm spacing (SDAS) measured in the standard thermal analysis cup with those obtained in the cylindrical test parts has been investigated. Thus, knowing the thermal modulus and the mould type it is possible to establish the required grain size and modification rate in the standard cup in order to get a desired structure in a real part. Corrective actions can then be taken in order to improve the metallurgical quality before casting the part.