The degassing process in aluminum alloy melting process can reduce the gas content in the molten aluminum and prevent the gas from precipitating during the solidification of aluminum alloy. If the gas content in liquid aluminum is very low, the amount of gas precipitated during solidification will be reduced, and the bubbles generated will also be significantly reduced. Therefore, the refining of aluminum alloy is a very important technological means. If the refining quality is good, there must be less blowholes; otherwise, if the refining quality is poor, there must be more blowholes. The measure to ensure the quality of refining is to select a good refining agent. A good refining agent can react to produce bubbles at about 660 ℃.
The bubbles generated are not too violent, but uniformly and continuously generate bubbles. Through physical adsorption, these bubbles fully contact with the liquid aluminum, adsorb the hydrogen in the liquid aluminum and bring them out of the liquid surface. Therefore, the bubbling time should not be too short, generally 6-8 min. When the aluminum alloy is cooled to 300 ℃, the solubility of hydrogen in aluminum alloy is only less than 0.001 cm3/100g, which is only 1 / 700 of liquid state. The pores produced by hydrogen precipitation after solidification are dispersed and small pinholes, which do not affect the air leakage and machined surface, and can not be seen by naked eyes.
In the production of aluminum alloy die casting, the pouring temperature of molten aluminum is generally 610-660 ℃. At this temperature, a large amount of gas (mainly H2) is dissolved in the molten aluminum. The solubility of hydrogen is closely related to the temperature of molten aluminum. The solubility of molten aluminum at 660 ℃ is about 0.69cm3/100g. The hydrogen content in liquid aluminum is about 19 times of that in solid state. Therefore, when the aluminum alloy solidifies, there will be a lot of hydrogen precipitation in the form of bubbles in the aluminum alloy die castings.
To ensure the degassing process in aluminum alloy smelting, select good refining agent and degassing agent, reduce the gas content in the liquid aluminum, and timely remove the surface scum, bubble and other oxides, so as to prevent the gas from entering the die casting parts again.