Novel Ceramic Foam Filter Materials for the Filtration of Magnesium Alloy Melts

Abstract

Cleanliness of magnesium alloy melts plays an important role in producing high-quality, lightweight products exemplary for the automotive or aircraft industry with high-quality standards. Therefore, the applicability of ceramic foam filters in the active and reactive filtration of magnesium alloys was explored as an option of metallurgical refining. Carbon-bonded alumina foams were selected in their uncoated as well as variously coated states. To evaluate the applicability of selected ceramic filter materials, various tests were applied, investigating filter properties, interface interactions, melt cleanliness and wetting behavior of the filter, such as sessile drop tests, immersion and filtration tests, and metallographic evaluation of AZ91. Immersion tests in AZ91 at 680 °C for up to 60 min showed the durability of coated and uncoated Al2O3-C and the formation of finely-structured MgO in-situ layers on any alumina- or spinel-containing surfaces in contact with molten AZ91. These layers, resulting from interface reactions with the melt, are regarded to have the potential to attract and bind oxidic inclusions from the metallic melt during filtration, as AZ91 samples showed reduced inclusion amounts after their contact with Al2O3-C filters. Another milestone was the synthesis of MgAlON as a filter coating, proven to be resistant towards the reactive magnesium alloy melt.