Thermal Analysis for the Prediction of Grain Refinement: an Experimental Investigation on an AlSiMg Foundry Alloy

Thermal analysis is widely used as a prediction tool for the quality of Al alloys before casting. In the present work, the effects of different grain refiners on the characteristic temperatures and on the g rain s ize o f α -Al phase were studied by thermal analysis and metallographic investigations. The response of an AlSiMg alloy towards grain refiners, added in form of rods and tabs, was investigated. In foundry practice, the fading phenomenon of grain refiners is well-known but not completely understood. For these reasons, the fading effect of each refiner at 60 minutes and 120 minutes holding times was also studied. Cooling curves and their derivatives were obtained during solidification of the alloys in a metallic crucible. Experimental data indicated the increase of the temperature associated with the nucleation of α-Al dendrites for the grain-refined alloys in comparison to the untreated ones. Simultaneously, a decrease in primary Al growth temperature, that led to the disappearance of the minimum temperature, were observed. Microstructural features revealed that an increase of 6 ÷ 7 °C of the nucleation temperature, compared to the not refined alloy, corresponds to a significant decrease in average grain size.