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Cast aluminum alloys can be divided into aluminum-silicon alloys, aluminum-copper alloys, aluminum-magnesium alloys, and aluminum-zinc alloys according to chemical composition.
â— Aluminum alloy casting process
The casting properties and chemical composition of aluminum alloys are closely related, among which the Al-Si alloy is near the eutectic composition and has good casting properties, similar to those of gray cast iron. The Al-Cu alloy is far from the eutectic composition, has a large solidification temperature range, and has poor casting properties. In practical production, aluminum castings are provided with feeders for feeding, Al-Si alloys have a small solidification temperature range, high feeding efficiency for feeders, and easy to obtain dense castings. Other types of cast aluminum alloys have a wide range of solidification temperatures, low feeder feeding efficiency, and poor casting compactness.
Aluminum alloys are very easy to inhale and oxidize, so the pouring system must ensure that the molten aluminum flows in quickly and smoothly, avoiding stirring.
Various casting methods are suitable for aluminum alloy castings. When the production volume is small, sand casting can be used, and fine sand should be used for molding. For mass production of important castings, special casting is used. Metal casting has high efficiency and good casting quality. Low-pressure casting is suitable for pressure-resistant castings requiring high compactness. Pressure casting can be used for thin-walled and complex parts.
â— Melting characteristics of cast aluminum alloy
Aluminum alloy is easily oxidized in liquid state. Its product is Al2O3. Its melting point is as high as 2050°C. Its density is slightly larger than that of aluminum. It is solid inclusions suspended in aluminum liquid. It is difficult to remove. It not only deteriorates the casting performance, but also reduces the mechanical properties. Density decreases. Aluminum liquid also easily absorbs hydrogen, precipitates when solidified, and forms defects such as pores or pinholes.
Refining method In order to slow the oxidation and inhalation of the aluminum liquid, the aluminum alloy should be melted under the flux layer. KCl, NaCl, etc. may be added to the crucible as a flux to isolate the liquid aluminum from the furnace gas. In order to drive off the hydrogen that has been sucked into the molten aluminum and prevent the generation of pinholes, hydrogen flooding and refining should be performed before the molten aluminum is discharged. There are various methods, and it is relatively simple to use a bell jar to press a chloride or chloride such as zinc chloride (ZnCl2) or hexachloroethane (C2Cl6) into the aluminum liquid, and the following reaction occurs:
3ZnCl2 + 2Al = 3Zn + 2AlCl3
3C2Cl6 + 2Al = 3C2Cl4 + 2AlCl3
The boiling point of the AlCl 3 formed by the reaction is 183° C., and the boiling point of C 2 Cl 4 is 121° C. Therefore, bubbles are formed. During the floatation process, the gases H 2 and Al 2 O 3 in the aluminum liquid are carried together with the liquid surface.
Melting equipment There are many kinds of aluminum alloy melting furnaces, and they are generally used for coke boilers. Resistor crucible boilers can also be used. In addition, induction furnaces (power frequency, intermediate frequency) are also used.
The structure of the alloy is much more complicated than pure metal. Because the alloy consists of two or more elements, the various elements interact to form various phases. We refer to homogeneous components in metals and alloys that have the same chemical composition, the same structure, and are separated from other parts by the interface.
According to this concept, the structure of pure metals and alloys is analyzed below. The pure metal is a single phase in the liquid state; the solid state is composed of the same element and the same crystal lattice, so it is a single phase; in the crystallization process, there are both the liquid phase and the solid phase, that is, two phases. When the alloy is in a liquid state, it is an alloy liquid having a uniform chemical composition and is a single phase. After the alloy changes from a liquid state to a solid state, the elements dissolve into each other to form a solid solution; the elements may also react with each other to form a metal compound. Solid solutions and metal compounds are the two basic phases of solid-state alloys. Therefore, in solid state, the alloy may be single-phase or multi-phase. In the analysis of the alloy structure, the phase structure is analyzed to see if it consists of several solid solutions or metal compounds, that is, several phases.
â— Aluminum alloy casting process
The casting properties and chemical composition of aluminum alloys are closely related, among which the Al-Si alloy is near the eutectic composition and has good casting properties, similar to those of gray cast iron. The Al-Cu alloy is far from the eutectic composition, has a large solidification temperature range, and has poor casting properties. In practical production, aluminum castings are provided with feeders for feeding, Al-Si alloys have a small solidification temperature range, high feeding efficiency for feeders, and easy to obtain dense castings. Other types of cast aluminum alloys have a wide range of solidification temperatures, low feeder feeding efficiency, and poor casting compactness.
Aluminum alloys are very easy to inhale and oxidize, so the pouring system must ensure that the molten aluminum flows in quickly and smoothly, avoiding stirring.
Various casting methods are suitable for aluminum alloy castings. When the production volume is small, sand casting can be used, and fine sand should be used for molding. For mass production of important castings, special casting is used. Metal casting has high efficiency and good casting quality. Low-pressure casting is suitable for pressure-resistant castings requiring high compactness. Pressure casting can be used for thin-walled and complex parts.
â— Melting characteristics of cast aluminum alloy
Aluminum alloy is easily oxidized in liquid state. Its product is Al2O3. Its melting point is as high as 2050°C. Its density is slightly larger than that of aluminum. It is solid inclusions suspended in aluminum liquid. It is difficult to remove. It not only deteriorates the casting performance, but also reduces the mechanical properties. Density decreases. Aluminum liquid also easily absorbs hydrogen, precipitates when solidified, and forms defects such as pores or pinholes.
Refining method In order to slow the oxidation and inhalation of the aluminum liquid, the aluminum alloy should be melted under the flux layer. KCl, NaCl, etc. may be added to the crucible as a flux to isolate the liquid aluminum from the furnace gas. In order to drive off the hydrogen that has been sucked into the molten aluminum and prevent the generation of pinholes, hydrogen flooding and refining should be performed before the molten aluminum is discharged. There are various methods, and it is relatively simple to use a bell jar to press a chloride or chloride such as zinc chloride (ZnCl2) or hexachloroethane (C2Cl6) into the aluminum liquid, and the following reaction occurs:
3ZnCl2 + 2Al = 3Zn + 2AlCl3
3C2Cl6 + 2Al = 3C2Cl4 + 2AlCl3
The boiling point of the AlCl 3 formed by the reaction is 183° C., and the boiling point of C 2 Cl 4 is 121° C. Therefore, bubbles are formed. During the floatation process, the gases H 2 and Al 2 O 3 in the aluminum liquid are carried together with the liquid surface.
Melting equipment There are many kinds of aluminum alloy melting furnaces, and they are generally used for coke boilers. Resistor crucible boilers can also be used. In addition, induction furnaces (power frequency, intermediate frequency) are also used.
The structure of the alloy is much more complicated than pure metal. Because the alloy consists of two or more elements, the various elements interact to form various phases. We refer to homogeneous components in metals and alloys that have the same chemical composition, the same structure, and are separated from other parts by the interface.
According to this concept, the structure of pure metals and alloys is analyzed below. The pure metal is a single phase in the liquid state; the solid state is composed of the same element and the same crystal lattice, so it is a single phase; in the crystallization process, there are both the liquid phase and the solid phase, that is, two phases. When the alloy is in a liquid state, it is an alloy liquid having a uniform chemical composition and is a single phase. After the alloy changes from a liquid state to a solid state, the elements dissolve into each other to form a solid solution; the elements may also react with each other to form a metal compound. Solid solutions and metal compounds are the two basic phases of solid-state alloys. Therefore, in solid state, the alloy may be single-phase or multi-phase. In the analysis of the alloy structure, the phase structure is analyzed to see if it consists of several solid solutions or metal compounds, that is, several phases.
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