What is the main reason of inclusion in liquid metal or solid ingot of aluminium? How to remove inclusion in liquid and solid of ingot?

The reason for the presence of inclusions in molten Al is beacuse it is extremely reactive, so when it comes in contact with moist air or wet tools, the water decomposes and hydrogen is released in the melt. This dissolved Hydrogen leads to porosity and shrinkage in castings and excessive quantities of this dissolved gas has negative effect on the properties of casting.

Methods to prevent inclusions:-

1.) Inert as well as reactive gases, or hexacholoroethane(C₂Cl₆) can be used to remove dissolved H₂ and Na.

2.) Fluxes based on KCl-NaCl mixture can be used to cover and protect the metal from oxidation.

3.) Mg may be removed by chlorine or aluminium-flouride containing fluxes.

Though C₂Cl₆ tablets provides effective degassing the noxious odor of the raw tablets creates environmental difficulties that have forced many foundaries to discontinue their use.

4.) So Rotary Degassing technique can be adopted to remove dissolved hydrogen.