Ultrasonic in-mold treatment of Al-Si alloys in sand casting process

Sand mold casting is a simple method for manufacturing large-scale aluminum castings with complex geometries. However, this process often leads to the development of coarse microstructures and significant porosities due to slow cooling rates. Suitable melt treatment techniques are required to eliminate those drawbacks. Ultrasonic treatment is known to refine the microstructure. Therefore, this work aims to investigate the effect of ultrasonic treatment on the macrostructure and microstructure of hypoeutectic Al-Si alloys (Al-7Si) in sand mold casting by using in-mold method. Ultrasonic vibrations were employed through a sonotrode that inserted into the top riser of a sand mold during the filling process to increase casting soundness by simultaneously promoting the structure refinement. The microstructure characterization revealed that the ultrasonic treatment resulted in refined α-Al grains. Moreover, the grain refinement contributed to refining the eutectic silicon phase, due to the restricted growth of eutectic during solidification. Furthermore, the ultrasonic treatment can enhance the hardness of the alloy.