Dr. Beate Fankhänel

Abstract:

The composition of the metal melt plays an important role in the production of high-quality aluminum castings. A melt with high hydrogen content often leads to defects and macro porosity [1]. Gas purging treatment and the use of melting salts for degassing are commonly used to reduce the hydrogen content. However, a consistent solidification of the entire cast part cannot always be realized. In these cases, undesired macro porosity may occur due to hydrogen excess in comparison to the amount of porous seeds in the melt. 

In recent years, the Institute of Nonferrous Metallurgy and Purest Materials has identified two ways of positively influencing this hydrogen porosity. On the one hand, it was found out that it is possible to use a special melt additive to adjust the ratio between the hydrogen dissolved in the melt and the existing pore nuclei so that the hydrogen released during solidification is finely distributed in the casting [2]. On the other hand, it was shown that the use of reactive filter materials can positively influence the precipitation of the atomically dissolved hydrogen and thus generate denser castings [3,4]. Both processes are presented and the efficiency and influence of the respective filter materials and additives is explained.