Effect of Sr–Grain Refining–Si Interactions on the Microstructural Characteristics of Al–Si Hypoeutectic Alloys

摘要

Abstract The present study was performed on A356.2 alloy to explore the link between the effectiveness of different grain refiner practices and strontium (Sr) modification on both the eutectic silicon (Si) particle morphology and the final grain size. To achieve this objective, several types of grain refiners were added to the molten alloy at 750?°C in different concentrations and for various holding times. Strontium was added in the amount of 200?ppm. Thermal analysis combined with microstructure analysis using optical microscopy and electron probe microanalysis was used to assess the results. It was found that Sr has a certain affinity to react with the boron (B) in Al–5%Ti–1%B master alloy which partially reduced the grain refiner effectiveness. The eutectic Si particles maintained a similar degree of modification as in the non-grain refined Sr-modified condition. Al–4%B used with Sr led to the formation of a new intermetallic (SrB~(6)), resulting in a significant decrease in the modification effect of Sr together with an increase in the obtained grain size. This effect increases at higher levels of added Al–4%B. The presence of excess Si leads to a change in the composition of the Al~(3)Ti phase into (Al, Si)~(2)Ti.