Influence of the Wetting Behavior on the Aluminum Melt Filtration

Although it is undisputed that the filtration of aluminum melt inside ceramic foam filters is influenced by the wetting behavior between the liquid melt and the material of the filter coating, experimental proof is still pending. For the present study, the contact angle of an AlSi7Mg alloy on substrates made of Al2O3, MgAl2O4, 3Al2O3·2SiO2 and TiO2 was measured by the sessile drop method at 730 °C using non-contact heating and capillary purification technique. The contact angles were compared with filtration efficiencies of filters with identical coating composition measured during filtration trials performed at a pilot casting line. For inclusions smaller than 110 µm, a correlation between contact angle and filtration efficiency was observed. Furthermore, adhesion forces of alumina inclusions on the four coating materials were experimentally determined using atomic force microscopy in a water-based model system. For inclusions larger than 70 µm, the filtration efficiency correlates with the measured adhesion force.