Effect of Electric Current (Plasma) Treatment on LM-6 Al-Si Alloy

Abstract

Molten eutectic aluminium-silicon (LM-6) alloys can be degassed by DC current treatment. The DC treatment ionises dissolved hydrogen in melt to H+ at the anode. The H+ ions flow through the melt towards the cathode by applied potential across the molten metal. At cathode, H+ ions are de-ionised and form molecules/gas, which escapes from melt due to lower pressure at that region. This process reduces dross formation. During solidification in a sand mould, the dissolved hydrogen in molten aluminium favours formation of primary silicon phase. Both DC and 50 Hz AC current treatments fragment primary silicon. Additionally, current treatment reduces gas porosity and modifies cast structures. In the degassed alloy, the current treatment stabilises primary alpha-phase, thus primary silicon is completely eliminated. It also reduces power consumption during turning in a lathe machine. There is a critical current density for the optimum effect.