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Causes of pinhole formation in aluminum castings

  • Author:kerry
  • Release on:2021-08-19

Pinhole is a kind of casting defect that can easily affect the casting quality in aluminum castings. Hydrogen is the main cause of pinhole (80-90 of the gas dissolved in aluminum liquid is hydrogen), and hydrogen is mainly produced by water vapor decomposition.  The main factor that directly affects the formation of pinhole is the cause of water vapor in aluminum alloy smelting process.

The main reasons affecting pinhole formation are:
In aluminium alloy smelting casting process, the use of raw materials, auxiliary materials, some materials in the water of crystallization and aluminum rust AL (OH) 2 decomposition can produce water, there are many kinds of organic and inorganic materials with molding materials of moisture, mold material in the supplementary material, coating and so on because preheat bad contain water and so on, in the aluminum alloy smelting casting,  A large amount of gas is produced by the decomposition of water vapor.  When different smelting equipment melts aluminum castings, the amount of suction of aluminum alloy and the degree of forming pores are different.  The new crucible and the old crucible with rust and dirt should be cleaned by blowing sand or other methods before use, and heated to 700℃-800℃, in order to remove the water and other chemicals absorbed by the crucible, because of the water contained in the melting and pouring of water vapor and the formation of pores.

Smelting tools such as ladle, degassing bell jar, etc., should be used before the surface of the residual metal, oxide scale and other dirt clean;  The tools used in aluminum magnesium alloy are required to be washed in carnallite and other flux before use.  If the preheating is not good, the surface of the water absorption, in the melting and pouring process due to heating the formation of water vapor and a large amount of gas, resulting in the formation of aluminum casting pinholes.