The microstructure and tensile properties were investigated in a thick-walled section (approximately 45 mm×43 mm) of a rheocast component produced by the RheoMetalTM process.Due to the long solidification period of such components, it is expected that the Al-Si eutectic formed will be coarse.Therefore, sodium (Na) was used as a modifying agent to reduce the coarseness of the eutectic.Tensile test bars were machined from three different sets of materials:1) non-modified melt, 2) modified melt cast directly after Na addition, and 3) modified melt cast 30 min after Na addition.The alloy used was a secondary AlSi6Cu2.5 alloy (STENAL Rheo1), specially developed for rheocasting.The material was studied in the as-cast condition as well as after a T6 heat treatment.The results show that the Al-Si eutectic is significantly refined by the Na addition, even after a fading time of 30 min.However, it is observed that the Na modification generally has a detrimental effect on the mechanical properties, despite the structure refinement.This is especially true in the T6 heat treated condition, where the yield strength is reduced by more than 30%.Some possible mechanisms for the degradation of mechanical performance are discussed.
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