Industrial suitable and digitally recordable application of ultrasound for the enviromentally friendly degassing of aluminium melts before tilt casting

Abstract

Aluminium casting alloys are important for numerous industrial applications. Due to the high affinity of aluminium melts for the absorption of hydrogen, hydrogen-related porosity is regarded as one of the main defects affecting the quality of castings. The use of rotor degassing and/or chemical degassing tablets prior to casting are state of the art to reduce the hydrogen content of the melt but require the use of additional substances and are often difficult to digitize. Due to its purely physical operating principle ultrasonic degassing (USD) is considered an environmentally friendly alternative to the established procedures and allows digital process monitoring. However, its small primary treatment zone, the cavitation zone, is the reason why the USD has so far been denied widespread industrial use. The approach presented here aims at an USD of aluminium casting alloy A356 in the basin prior to tilt casting. Here the melting volumes are sufficiently small. By using Particle Image Velocimetry (PIV) analyses, CFD simulation and casting tests, this case of application was systematically investigated. It could be shown that the approach followed contributes to a significant reduction of the hydrogen dissolved in the melt by more than 50 % resulting in an increase of mechanical properties, especially elongation.