In the process of zinc alloy die casting, gas is dissolved in the metal through adsorption, diffusion and dissolution into the metal, but the dissolution rate mainly depends on the diffusion rate. As a gas that is easily soluble in metals, how does hydrogen affect liquid aluminum?
In the chemistry of the zinc alloy die-casting process, hydrogen does not react with aluminum. The way it affects liquid aluminum is mainly to form an interstitial solid solution in the ion state in the lattice gap. The dissolution of hydrogen is related to the temperature and pressure of the melt. Under a certain pressure, the solubility of hydrogen in aluminum increases with temperature. The greater the solubility and the lower the temperature, the lower the solubility of hydrogen in aluminum.
When the aluminum alloy changes from a liquid state to a solid state, the solubility of hydrogen changes greatly. Under the direct water-cooling casting conditions of aluminum alloy die-casting, due to the rapid water-cooling speed, the final hydrogen precipitates into molecular hydrogen. It is too late to exclude the melt and enter the mold. Porosity and pores in the mold can cause defects, such as looseness and pores in zinc die-cast aluminum alloy die-casting parts, which will affect the use of die-casting parts.
The fine equiaxed crystal area of the aluminum alloy die-casting plant is produced under the dual action of the strong cooling of the mold wall and the convection of the liquid metal.
In the zinc alloy die-casting process, when the liquid metal is poured into the low-temperature mold, the liquid in contact with the mold wall is strongly cooled, and the supercooled liquid near the mold wall will produce a large number of crystal nuclei to form fine equiaxes The crystal region creates thermodynamic conditions. At the same time, due to the momentum convection caused by the liquid flow and the temperature change caused by the temperature difference between the inside and outside of the liquid during the casting process, the crystals on the surface of the mold wall fall off and re-solidify, thereby increasing the solidification area. Therefore, the crystal nucleus The number of is formed on the surface of the small equiaxed crystal area.
