Porosity is the most common problem of high-pressure aluminum castings. The improvement and elimination of porosity of high-pressure aluminum castings are put forward as follows:
1. Guarantee the degassing quality of aluminum alloy smelting, the surface and tools of alloy ingot are dry, and the return charge is clean. Select good refining agent, degassing agent, control melting temperature, avoid overheating, reduce the amount of gas in the aluminum liquid, degassing processing. Remove liquid scum, bubble, and other oxides in time to prevent the gas into the high-pressure aluminum casting.
2. Select a good demolding agent and spraying process, choose a good release agent which doesn't produce gas in the die casting and has good ejection performance.
3. Make sure that the mold exhaust groove, overflow groove position is correct. The sequence filling is conducive to gas discharge from the cavity, unobstructed exhaust. The smooth exhaust ensures the complete discharge of gas in the mold. Especially in the final convergence of aluminum liquid, the exhaust channel must be clear. The sprue and runner shall be of sufficient length (>50mm) to facilitate the smooth flow of the alloy and the opportunity for gas discharge. It can change the thickness, the direction of the gate, and set overflow groove and exhaust groove at the position where the air hole is formed. The total cross-sectional area of the overflow products shall not be less than 60% of the total of the internal sprue, or the slag discharge effect will be poor.
4. Select the coating with good performance and control the spraying amount.
5. Adjust the parameters of high-pressure aluminum casting, especially the injection speed. Have a good command of the casting temperature and keep the filling speed not too fast so as to achieve an orderly and stable flow state and prevent separation and eddy current from forming air entrapment.
6. Pay attention to core-pulling and cooling to minimize excessive wall thickness differences in product design and mold design.
7. For the pores that often appear at the fixed position, it is necessary to improve the mold and design, whether there are sharp corners or dead zones, and whether there are changes in the cross-sectional area of the gating system. Computer simulation of the filling process is used to select reasonable technological parameters.
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