Die Casting Knowledge(1)

- Jun 02, 2019-

1.The higher the melting temperature of the alloy, the longer the melting time and the holding time of the molten aluminum after melting, the more fully the hydrogen diffuses in the aluminum liquid, the greater the hydrogen absorption of the aluminum liquid, and the greater the probability of pinholes. Some people have done experiments. The longer the aluminum liquid is stored, the more the gas content in the aluminum alloy increases proportionally.

2.Pinhole is a casting defect that is easy to appear in aluminum alloy castings and has a certain influence on the quality of castings. Hydrogen is the main cause of pinholes (some data show that 80%-90 of the dissolved gases in aluminum liquid % is hydrogen), and the main source of hydrogen is produced by the decomposition of water vapor. Therefore, the cause of water vapor generation in the aluminum alloy during the smelting process is the main factor that directly affects pinhole formation.

3.When aluminum alloy is smelted, it takes a process to dissolve the hydrogen into the aluminum liquid. Therefore, the control of the smelting process is enhanced, and there is much to be done to control the amount of gas absorbed by the aluminum alloy. Production practice shows that the hydrogen absorption of aluminum liquid is carried out on the surface, which is not only related to the partial pressure of the surface of the aluminum liquid, but also has a great relationship with the melting temperature and melting time of the alloy. The higher the melting temperature of the alloy, the longer the melting time and the holding time of the molten aluminum after melting, the more fully the hydrogen diffuses in the aluminum liquid, and the greater the hydrogen absorption of the aluminum liquid, the greater the probability of pinholes. Some people have done experiments. The longer the aluminum liquid is stored, the more the gas content in the aluminum alloy increases proportionally. Therefore, under a large number of production conditions, in order to reduce the absorption of hydrogen during the melting of aluminum alloy, it is necessary to strictly implement the aluminum alloy melting process.

4.The oil, organic matter, salt flux, etc. brought in by the metal charge or the recycled material can also generate hydrogen by reacting with the aluminum liquid.

5.At present, in order to eliminate pinholes in aluminum alloy castings, the most common method is to degas with chlorine and chloride during the melting process, degas with chlorine, nitrogen, degas with vacuum, degas with ultrasonic, filter degassing, etc. method. When degassing with chlorine salt and chloride deaerator, use a bell jar to press the deaerator into the bottom of the crucible 100mm and move it evenly along the circumference of the 坩埚 diameter 1/3 (from the inner wall of the crucible). In order not to spray a large amount of aluminum liquid, the deaerator can be added in batches, and the degassing is finished.

6.Surface pores and bubbles can be found by sand blasting. The internal pores and bubbles can be found by X-ray or machining, and the bubbles are black on the X-ray film.