Melting characteristics of aluminum alloys

[China Aluminum Industry Network] Aluminum alloy melting characteristics The smelting of aluminum alloys has characteristics such as high heat consumption, easy oxidation, easy hydrogen absorption, and easy absorption of impurity metals. 1) Heat consumption Although the melting point of aluminum is low, the latent heat of fusion is large, the specific heat is large, the blackness is small, and the reflection of heat is strong. Compared with other common metals such as iron and copper, the aluminum melts consume more heat. 2) Easily oxidized Aluminum has a great affinity for oxygen and it can oxidize very quickly to form Al2O3. Although the aluminum oxide film formed on the surface of the melt has a protective effect, once it is destroyed, the oxide film enters the melt and is difficult to remove. Because one Al2O3 is not easy to reduce, its density is similar to that of the melt. It is suspended in the melt and enters the ingot with the melt, which adversely affects the quality of the processed material. What is more serious is that aluminum oxide is a good carrier for various gases, and its presence causes the aluminum melt to absorb a large amount of hydrogen. Therefore, reducing oxidation as much as possible is an important issue in the smelting process of aluminum alloys. 3) Easy to inhale Aluminum and aluminum alloys have a strong ability to get air (mainly the ability to absorb hydrogen), especially in furnace gases with water vapor or reducing atmosphere. Although the amount of hydrogen absorbed by aluminum and aluminum alloys is not large, at the melting point, the solubility of hydrogen in the solid phase and the liquid phase largely differs, and the tendency of the formation of pores and porosity during the crystallization of the ingot is large. Therefore, minimizing hydrogen absorption is another important issue for the smelting of aluminum and aluminum alloys. 4) Easy to absorb metal impurities Some alloying elements in aluminum and aluminum alloys are highly chemically active. They not only absorb iron dissolved directly from iron cerium and tools, but also neutralize many chlorine salts of the flux from many oxides of the furnace lining. Displace iron, silicon, zinc and other metal impurities. Once these metal impurities enter the aluminum melt, they cannot be removed. And the more melting times, the higher the impurity content, the greater the impact on the performance of the alloy, so that when the grade of pure aluminum is degraded, the alloy composition will be exceeded and scrapped. Therefore, the prevention of contamination of metallic impurities is the third important issue in the smelting of aluminum and aluminum alloys.