Briefly, why do pores occur in production?
Release time:2024-01-15
Briefly, why do pores occur in production?
Pores caused by poor quality degassing of essence
In the production of casting-china.com' target='_blank'>aluminum alloy die casting, the pouring temperature of liquid aluminum is generally 610-660℃. At this temperature, many gases (mainly hydrogen) are dissolved in aluminum liquid, and the solubility of hydrogen in aluminum alloy is the same as that of aluminum alloy. Temperature is closely related. It is about 0.69cm3/100g in liquid aluminum liquid at about 660 ° C, and only 0.036cm3/100g in solid aluminum alloy at about 660 ° C. At this time, the hydrogen content of liquid aluminum is about solid. 19 or 20 times. Therefore, when the aluminum alloy condenses, a lot of hydrogen is separated in the form of bubbles in the aluminum alloy die casting.
In order to reduce the gas content in liquid aluminum and prevent a lot of gas separation pores from occurring when aluminum alloy condenses, this is the intention of refining degassing during aluminum alloy smelting. If the gas content in the liquid aluminum is reduced, the amount of gas released during condensation will be reduced, and the resulting bubbles will also be significantly reduced. Therefore, the essence of aluminum alloy is a very important process method. The quality of the essence is good, the porosity is less, the quality of the essence is poor, the porosity is more. The measure to ensure the quality of the essence is to select a good essence agent. A good essence can react with bubbles at about 660℃. The bubbles that occur are not too strong, but occur in a uniform and continuous pattern. When the aluminum liquid is fully in contact, the hydrogen in the aluminum liquid is absorbed and carried out of the liquid surface. Therefore, the foaming time should not be too short. The general foaming time is 6 to 8 minutes.
When the aluminum alloy is cooled to 300 ° C, the solubility of hydrogen in the aluminum alloy is only less than 0.001cm3/100g, which is only 1/700 of the liquid state. The pores of hydrogen evolution after condensation are lax and small. Pinhole, does not affect the air leakage and processing appearance, the naked eye can not see.
The bubbles produced by hydrogen evolution during the condensation of liquid aluminum are relatively large, and most of them are located in the core of the final condensed liquid aluminum. Although they are also lax, these bubbles often lead to leakage, and when severe, they often lead to the abandonment of the workpiece.
