ã€China Aluminum Industry Network】 1. Melting Characteristics of Aluminum Alloys The melting of aluminum alloys has characteristics such as high heat consumption, easy oxidation, easy hydrogen absorption, and easy absorption of impurity metals.
1) Heat consumption The melting point of many aluminum is low, but it has large latent heat of fusion, large specific heat, small blackness and strong reflection of heat. Compared with other commonly used metals such as iron and copper, it consumes more heat when melting.
2) The easy alumina 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-sucking Aluminium and aluminum alloys have a strong ability to get air (mainly the ability to absorb hydrogen), especially in furnace gas with steam 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 of the alloying elements in aluminum and aluminum alloys have high chemical activity. They can not only absorb iron directly from the iron crucibles and tools, but also can be neutralized from many oxides of the furnace lining. Many chlorine salts of fluxes displace metal impurities such as iron, silicon, and zinc. 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.
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