First of all, it is the improvement of the smelting operation. It is necessary to fully preheat the recycled materials with organic matter, aluminum rust and other impurities to prevent the hydrogen content of the aluminum water after melting; minimize the melting time and reduce the absorption during the melting process. Hydrogen; then the aluminum oil is fully refined and degassed. The best way is to use a rotary air refiner to refine and deaerate the aluminum water, and it is best to use high purity argon as the gas source; Pure nitrogen is also good, but when the temperature of aluminum water is too high or the content of magnesium is very large, the problem of excessive slag is likely to occur; as for the mold, it should be improved without affecting the complete molding of the casting and other defects. The cooling rate of the mold shortens the solidification time of the aluminum water in the cavity, and it is also beneficial to prevent the hydrogen element contained therein from being precipitated into a pinhole. However, after all, it is not a problem. It is best to try to completely remove hydrogen, including some details.