Degassing is the injection of inert gas into molten aluminum for the purpose of removing hydrogen. Additionally, degassing is also referred to as a flotation method of inclusion removal.

There are primarily two theoretical models which have been proposed to explain how degassing works. The macroscopic model contends that the removal of every impurity is similar in nature.

The microscopic model maintains that the removal of impurities is based on phenomenon that occur at the bubble/liquid metal interface.

According to the theory, the dissolved hydrogen diffuses into the gas being injected into melt, due to its high vapour pressure. Alkalies also diffuse into the injected gas. In theory, inclusions as small as 10um in diameter which come in contact with a bubble attach themselves to it and float to the melts surface.

There are four factors which effect the hydrogen and inclusion removal rate in molten aluminum:

1. Metal flow rate or volume

2. Inert gas flow rate

3. Dispersion of inert gas

4. Contact of the inert gas with the impurities