Pinhole Formation In Aluminum Castings
| Pinholes are a casting defect that easily occurs in aluminum castings and has a certain effect on the quality of machining castings. |
Hydrogen is the main cause of pinholes (80-90 of the gas dissolved in the aluminum liquid is hydrogen), and hydrogen is mainly generated by the decomposition of water vapor.
The cause of water vapor generation during the melting process of aluminum alloy is the main factor that directly affects the formation of pinholes. The main factors affecting the formation of pinholes are:
During the aluminum alloy smelting and pouring process, the raw materials, auxiliary materials, crystal water in some materials, and aluminum rust AL (OH) 2 are decomposed to generate moisture.
There are many organic and inorganic auxiliary materials in the modeling material. Moisture contained in casting materials such as auxiliary materials and coatings due to poor preheating will generate a large amount of gas due to the decomposition of water vapor during aluminum alloy melting and pouring. When different melting equipment melts aluminum die castings, the amount of air intake of aluminum alloy and the degree of formation of pores are different.
New crucibles and old crucibles with rust and dirt should be blown sand or removed by other methods before use, and heated to 700 ℃ -800 ℃ to remove the water and other chemical substances absorbed by the crucible. Water vapor is generated during smelting and pouring to form pores.
For smelting tools, such as ladle, degassing bell cover, etc., the surface metal, oxide scale and other dirt should be removed before use; tools for aluminum-magnesium alloy should be placed on carnallite before use Wash in flux.
If the preheating is not good, the moisture absorbed on the surface will generate a large amount of gas due to heating to form water vapor during the melting and pouring process, resulting in the formation of pinholes in aluminum castings.
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Link to this article：Main Factors Of Pinhole Formation In Aluminum Castings
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