Pinhole is a casting defect which is easy to appear in aluminum castings and has a certain influence on the casting quality. Hydrogen is the main reason for pinhole formation (80-90 of the dissolved gas in molten aluminum is hydrogen), while hydrogen is mainly produced by steam decomposition. The cause of the production of water vapor in the melting process of aluminum alloy is the main factor that directly affects the formation of the pinholes. The main factors affecting the formation of pinholes are:
In the Aluminum Alloy melting and pouring process, the use of raw materials, auxiliary materials, some materials of crystal water and aluminum rust AL (OH) 2 decomposition will produce water, there are a variety of organic and inorganic materials with water modeling materials, casting material in the coating materials, because the pre poor heat moisture so, in the melting and pouring of Aluminum Alloy, will produce large amounts of gas due to decomposition of water vapor. When aluminum castings are melted by different smelting equipment, the amount of suction and the formation of air holes are different in the aluminum alloy. The new crucible is rust, dirt and old crucible, before use should be cleaned with blowing sand or other methods, and heated to 700 DEG -800 DEG, to remove the crucible by adsorption of moisture and other chemical substances, because of containing water and water vapor generated in the melting casting and the formation of porosity.
Use tools such as smelting ladle, degassing with bell, before use should be cleaned, the surface residual metal oxide impurities; aluminum magnesium alloy tools, before it is used on the flux washing clean carnallite etc.. If the preheating poor surface adsorption of water, in the process of melting and pouring of water vapor is formed by heating and produce large amounts of gas, resulting in the formation of pinholes in aluminum castings.
