In addition to the need for suction during melting, aluminum parts also need suction during pouring into the mold. At this time, the liquid metal entering the mold will decrease with temperature, and the gas itself The solubility will also decrease, and the excess gas in the equipment will be diluted, but there will still be a small part of the gas that will remain in the casting and some pores will form. This is what we usually call pinholes. In this way, the shrinkage pores are easily bonded to the gas, and the gas diluted in the aluminum liquid will continue to remain in the shrinkage pores. If the air bubbles generate great pressure due to heat, the surface of the pores will be particularly smooth, so that the perimeter of the pores will be said to have a significant brightness. If the pressure of the air bubbles is small, then the surface of the pores will have a lot The wrinkles feel like the feet of a fly, but if you look closely, they will still have the characteristics of shrinkage.
The higher the hydrogen content in the liquid of aluminum parts, the more pinholes can of course be produced by the casting. Pinholes in aluminum parts can effectively reduce the corrosion resistance and air tightness of the casting itself, and can also reduce the mechanical properties of the alloy to a certain extent. If you don't want the aluminum parts to have porosity or less porosity, the main thing is the smelting conditions. If the protection of the covering agent can be added during the smelting process, the gas absorption of the alloy will be greatly reduced. If you want to effectively control the hydrogen content in the molten aluminum. The solution was to refining the aluminum melt.