Melting characteristics of aluminum alloys


Melting characteristics of aluminum alloys

The chemical composition, impurity content and gas content of the alloy will affect the mechanical properties of the alloy, the shrinkage of the casting and the surface tension of the molten aluminum. Impurity elements greatly reduce the surface tension of aluminum, and the surface tension affects the gas diffusion during the filling process, thereby affecting the distribution of pores.

1. Oxidation. Aluminum has a great affinity for oxygen, and it is easy to form an oxide film AlOg when aluminum and its alloy liquid contact with air. Although the oxide film on the surface of the melt is protected, if it is destroyed by stirring and tumbling, oxygen enters the melt and is not easy to remove. First, Al Og is not easy to reduce, and second, its density is similar to that of the melt, and it is suspended in the melt. In the body, it is easy to enter the casting with the melt.

2. Hydrogen absorption. Liquid aluminum can easily absorb hydrogen from the atmosphere, the moisture on the surface of alloy ingots or tools, and the burning oil and gas. The solubility of hydrogen in solid five aluminum is very low, so when there is too much hydrogen absorption, it is in a saturated state during solidification, and hydrogen will be precipitated, causing pores and shrinkage in the casting.

3. Impurities. Common inclusions in the aluminum alloy melt are Al20g, Sio, Mgo, etc., which will cause the impurity of the molten metal. Inclusions affect the fluidity of the melt, and polymerize in the die casting to generate bubbles, which affect the degree of shrinkage.

4, slag. Slag formation occurs due to the reaction between the aluminum alloy liquid and the iron crucible lining. Some sesame-sized black and gray particles were visible on the cut surface of the casting. There are non-metallic oxides, metallic slag (Si) or metallic compounds, composite slag, and segregation slag.

5. Increase iron. The molten aluminum has a certain erosion effect on the crucible, the pouring spoon and the mold, which leads to the increase of iron, and the iron content in the returned charge is far greater than the iron content specified in the new material.

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