The effect of combining smooth moul

The effect of combining smooth mould cavity filling and ultrasonic degassing by using the Low Pressure Sand Casting process with US melt treatment on the microstructure and mechanical properties of AlSi7Mg0.3 alloy was investigated. The main conclusions can be drawn from the developed study:• Besides melt degassing, the ultrasonic degassing treatment at lowertemperatures favours the grain refinement of the α-Al primaryphase when compared with treatment at higher temperatures, leading to globular microstructures with small grain size. In fact, at650 °C ultrasonic degassing has a microstructure refinement potentialsimilar to traditional chemical refinement routes.• The pressurization rate, then the mould filling velocity, has great influence in the development of oxide films, which remain entrapped inthe melt after solidification. Oxide formation can be avoided usingpressurization curves than lead to melt velocities lower than 0.5 m/s.• The significant improvement in microstructure, both in what concerns to the microstructure morphology and the absence of porosityand oxides promote an increase in the ultimate tensile strength ofthe alloy, which reached 253 MPa for a pouring temperature of 650 °C.• It was shown that increasing of filling velocity decreases the value ofWeibull modulus.