Principle and source of gas and inclusion in liquid aluminum

1.Principle：

When the alloy is in solid state, the solubility of the gas is very small, and the melting degree increases slowly with the increase of temperature. When the melting point of the alloy is reached, the melting degree suddenly increases rapidly. When the alloy is melted and then heated up, the melting degree increases faster, because the melted alloy has a very active chemical reaction with the atmosphere, absorbs hydrogen, and is oxidized and produces oxides. It also consumes the effective components in the molten liquid, which reduces the quality of the solution, or forms defects such as pores and slag inclusion.

2.Sources of gases and inclusions in liquid aluminum：

Aluminum alloy is smelted in a certain furnace gas, in high temperature with N2, O2, H20, CO2 in the furnace gas contact, interaction occurs on the contact interface, resulting in combination, decomposition, dissolution, diffusion and other processes. Various chemical reactions are as follows:
4Al + 30₂ = 2Al₂0₃
2Al+ N₂= 2AIN
2Al+ 3H₂0= Al₂O₃+6[H]
2Al + 3C0₂= Al₂0₃ + 3CO
6Al+ 3CO= Al₂O₃+ Al₄C
Al₄C₃ + 60₂= 2Al₂0₃+ 3CO₂
  It can be seen from the above reaction that aluminum liquid and various gases can react to produce aluminum nitride, aluminum carbide, aluminum oxide, etc. Aluminum nitride and aluminum carbide can also be further reacted to produce alumina. Alumina has high chemical stability, does not decompose in aluminum liquid, and is the main inclusion in aluminum liquid. In addition to the above alumina, aluminum nitride, aluminum carbide inclusions, aluminum melt also contains furnace, ladle refractory blocks, solvents and other inclusions.
  According to the test analysis, whether it is liquid aluminum or solid aluminum, the dissolved gas is mainly hydrogen, so the "gas content" of aluminum alloy can be approximately regarded as "hydrogen content". The main source of hydrogen in aluminum alloys is H2O in the furnace gas. Experiments and production practice have proved that the main way of hydrogen dissolving into aluminum liquid is due to the reaction of water vapor and aluminum liquid, so as to generate atomic hydrogen, and establish a large hydrogen partial pressure on its interface, so that the amount of hydrogen dissolved in metal liquid rapidly and greatly increased.

Material from the Internet, if there is infringement, please contact delete.