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In the production process, in order to avoid the defects of aluminum alloy pores, effective measures must be taken to reduce the moisture of the raw materials as much as possible, strengthen the quality management of the smelting, and improve the exhaust energy of the mold. The details are as follows:
The main reason for the pores in the casting is that the aluminum alloy contains excessive H. The hydrogen content accounts for% ～% of the total gas content. The rest is N, O CO, etc., and H is derived from the atmosphere and various metal raw materials and flux And the moisture in the coating is differentiated by heat, and the HO = H + + O-reaction occurs under high-temperature conditions, which is a reversible reaction. The differentiated oxygen easily generates AlO with a higher melting point with the molten metal. The reaction equation is: Al + + O-= AlO. This promotes the high-temperature differentiation of water vapor and the hydrogen ions are continuously dispersed into the alloy liquid.
Hydrogen exists in the aluminum solution in two ways: the first is to differentiate into atomic conditions and dissolve in the aluminum solution, which is called dissolved type, accounting for about%; the second type of hydrogen is adsorbed to the appearance of inclusions in the form of molecular bubbles Or in the gap, it is called adsorption type. Since the solubility of hydrogen in the aluminum alloy liquid increases with temperature, the alloy liquid will absorb a lot of H during the melting process. In the process of crystallization and condensation, due to the temperature drop, the surface layer of the alloy liquid mainly condenses and the viscosity of the alloy increases. Although the decrease in the solubility of hydrogen needs to be separated from the metal liquid, it is now difficult to stay in the alloy liquid. This constitutes a stomata defect. The longer the melting and holding time, the higher the hydrogen content.
Aluminum Alloy Die Casting
The solubility of tritium hydrogen in the alloy liquid is not only proportional to the temperature, but also proportional to the pressure and the humidity of the air, that is, the partial pressure of hydrogen.
Aluminum alloy elements and their content also have a certain effect on the solubility. When the content of silicon and copper is added, the solubility of hydrogen decreases, and when the content of magnesium is added, the solubility of hydrogen is added. With different aluminum alloy components, the critical content of hydrogen in the alloy liquid is also different. ZL aluminum alloys have the largest hydrogen absorption when they are hypoeutectic aluminum-silicon alloys.
Aluminum Alloy Die Casting is a casting process for high-temperature and high-speed injection of molten aluminum alloy metal liquid into a mold cavity. This casting method is characterized by precise product formation and high production efficiency. However, the conventional die-casting process has defects. Because the gas in the mold cavity cannot be effectively eliminated during high-speed injection, it remains inside the casting, forming porosity defects, resulting in poor mechanical properties of the casting. In order to solve this problem, people use a vacuum method, that is, the gas in the cavity is drawn out during die casting to form a certain vacuum or negative pressure state, thereby reducing the porosity defects in the casting.
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