T. Doppler, H. Antrekowitsch, H. Boettcher, W. Fragner
Aluminium melts with magnesium show characteristic oxidation behaviour and it is possible that the
oxidation rate suddenly increases. This phenomenon is known as breakaway oxidation and has to be
avoided in the casthouse. Therefore it is necessary to define the parameters which cause these undesirable
reactions. Trace elements in the input material like calcium could have a possible influence
on this effect. Different investigations for proofing this hypothesis and for evaluating the quality of
different sources of magnesium were done. Especially the beginning of the breakaway oxidation as
well as the effect of Ca was studied.
Therefore the dross formation on AlMg5-melts was investigated in a resistance furnace at a scale of
30 kg. The binary alloy was produced using primary aluminium and magnesium. Calcium was added
via a master alloy. After alloying, the melt was skimmed and held at 740 °C for eight hours under
standard atmosphere conditions (air, 1 atm). The temperature of the melt was measured continuously
and at the end of the holding period the dross was skimmed. To consider a possible influence of the
atmosphere, thermogravimetric analysis (TGA) were carried out at 740 °C under furnace atmosphere
conditions and synthetic air at samples that were taken from the resistance furnace.