aluminium silicon alloy (aluminium silicon alloy) is a forging and casting alloy with aluminum and silicon as the main components. The general silicon content is 11%, while adding a small amount of copper, iron and nickel to improve the strength. The density is about 2.6 ~ 2.7g/cm3, and the thermal conductivity is about 101 ~ 126W/(m·ºC). Young's modulus is 71.0GPa, the impact value is about 7 ~ 8.5J, and the fatigue limit is ±45MPa.
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Because of its light weight, good thermal conductivity, strength, hardness and corrosion resistance, AI-Si alloy is widely used in the automobile industry and machine manufacturing to make some parts used under sliding friction conditions.
l-Si alloy is a very important industrial alloy, widely used in aviation, transportation, construction, automobile and other important industries, is also used in the manufacture of low and medium strength of the shape of complex castings, such as cover plate, motor housing, bracket, and also used as brazing solder. The alloy is a typical eutectic alloy with simple phase diagram and no intermediate compounds. It has the advantages of good casting performance, high strength and low price. Aluminum is the third main group element, and silicon is the semiconductor element, the solid solubility of each other is very small. [2]
Performance and use
When the silicon content is low (such as 0.7), Al-Si alloy has good ductility and is commonly used as deformation alloy. When the silicon content is higher (such as 7%), the aluminum-silicon alloy melt is better filled and is often used as casting alloy. When the silicon content exceeds the Al-Si eutectic point (silicon content is 12.6%) and the silicon particle content is up to 14.5% ~ 25%, the comprehensive mechanical properties can be improved by adding a certain amount of Ni, CU, Mg and other elements. They can be used in car engines instead of cast iron cylinders with significant weight reduction. The aluminum silicon alloy used as cylinder can be treated by electrochemical process to etch the surface aluminum and retain the primary silicon particle embedded in the matrix inside the cylinder wall, and its abrasion resistance and abrasion resistance can be significantly improved. Among them, the alloy with 11% ~ 13% silicon content is one of the best piston materials for its light weight, low expansion coefficient and high corrosion resistance.
Electrothermal production
The metallurgical temperature of aluminum silicon alloy produced by electric heating is about ºC. In the process of metallurgy, alumina and silicon oxide are liquid, which are generally reduced by carbonaceous reducing agent. Generally, the highest temperature of mineral furnace can be reached is about ~ºC.
Component and organization editorial broadcast
Al-si binary alloy has a simple eutectic phase diagram, as shown in the "Al+Si Binary Phase Diagram". At room temperature, there are only α (Al) and p (Si) phases. The properties of α (Al) and β (Si) are similar to those of pure silicon. The Si content of eutectic alloy is 12.6%. The microstructure of subeutectic alloy is composed of α (Al) + eutectic crystal (α+p), and that of hypereutectic alloy is composed of β (Si) + eutectic crystal (α+β). Due to the introduction of trace phosphorus into crystalline silicon, even 10ppm of phosphorus to AlP is sufficient to produce primary silicon in a 9% Si subeutectic alloy and cause the eutectic silicon to form coarse plates.
With the increase of silicon content, the crystallization temperature interval decreases, the eutectic crystal increases, and the fluidity increases. When the shrinkage rate of silicon is very small, the linear shrinkage rate of the alloy also decreases, and the hot cracking tendency decreases accordingly. The latent heat of crystallization of silicon is large, and the fluidity is still higher than that of eutectic alloy until the content of Si reaches 20%. When the Si content is 16% ~ 18%, the liquidity peak.
Although eutectic AI-Si binary alloy has excellent casting properties, it can only be used for high-speed cooling casting methods such as die casting and extrusion casting because of its poor mechanical properties. For sand casting, gypsum casting and other casting methods with slow cooling rate, metamorphic treatment must be carried out to refine eutectic silicon in order to obtain adequate mechanical properties.
The modification process of refining eutectic silicon cannot also refine primary silicon. For hypereutectic alloys with a large amount of primary silicon, phosphorus must be added to refine primary silicon to improve mechanical properties.
The silicon content has an effect on wear resistance, corrosion resistance, linear expansion coefficient, density and conductivity of Al-Si binary alloy. With the increase of silicon content, the wear, corrosion, linear expansion coefficient, density and conductivity all decrease linearly.
Aluminum plasticity is large, cutting need to consume a lot of work, with the increase of silicon, eutectic increase, cutting work can be reduced, but eutectic silicon hardness is high, easy to wear the tool, especially the coarse initial silicon of the eutectic alloy, tool wear is more serious, the surface of the processing is very rough. In order to improve the machinability, besides corresponding modification treatment, refining eutectic silicon and primary silicon, bismuth, lead and other easy machinable elements can be added. For hypereutectic alloys, diamond cutting tools can be used, and the best cutting speed and suitable cutting fluid can be selected to obtain smooth machining surface.
To sum up, in order to take into account various service properties and technological properties of the alloy, the silicon content of Al-Si alloys is generally 7% ~ 12%.
The representative of Al-Si binary alloy is ZL102 alloy, the composition is 10% ~ 13% Si, the rest is aluminum, the metallographic structure is α (Al) + eutectic (α+β) and a small amount of primary silicon. ZL102 alloy has the following characteristics.
1) The strengthening effect of heat treatment is small and the mechanical properties are not high
The solubility of silicon in α (Al) solid solution is 1.65% at 577ºC and decreases to 0.05% at room temperature. However, the strengthening effect of heat treatment is not large, and artificial aging after solid solution treatment can only increase the strength of alloy by 10% ~ 20%, because silicon precipitation and accumulation speed is very fast, even in the process of solid solution treatment may occur solid solution decomposition, silicon particle precipitation, no coherent or semi-coherent transition phase, so generally only annealing to eliminate the internal stress. The mechanical properties of ZL102 are not high.
2) Excellent casting performance
The near-eutectic Al-Si binary alloy has a small crystallization temperature interval and a large crystallization potential heat of silicon, so the fluidity is the crown of the cast aluminum alloy, and the tendency of concentrated shrinkage cavity is large. A reasonable riser should be set to obtain dense castings, which will not cause leakage until the destruction. Silicon reduces the solubility of hydrogen after the solidification of liquid aluminum, and pinholes are easy to be produced if the refining is improper.
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3) Good wear resistance, corrosion resistance and heat resistance
Al-si binary alloy has soft phase α (Al) and hard phase silicon, and is a typical wear-resistant structure with good wear resistance. The electron potential difference between α (Al) and eutectic silicon is not much. The surface layer of Al2O3 is dense and has a protective effect on the matrix, so the corrosion resistance is good. The eutectic temperature of ZL102 alloy is 577ºC, which is higher than that of other cast aluminum alloys. There is no phenomenon of dissolution or aggregation of enhanced phase when the temperature rises, so the heat resistance is the best.
4) Metamorphic treatment must be carried out to improve mechanical properties
The mechanical properties before metamorphism are low, and the machining properties are poor, so it is necessary to undergo metamorphic treatment, so that the lamellar eutectic silicon can be changed into fibrous, and the primary crystalline silicon can be eliminated to greatly improve the mechanical properties.
In summary, ZL102 alloy is suitable for die casting or corrosion resistance, wear resistance; Thin wall, complex castings to withstand small and medium loads, such as the frame, bright body, base of various instruments, etc. [3]
Spoilage treatment editor broadcast
The significance of metamorphic treatment
Cast aluminum-silicon alloy has the advantages of low density, high strength, good wear and heat resistance, small thermal expansion coefficient and so on. It is the most widely used and the most productive alloy in cast aluminum alloy. The typical eutectic phase diagram shows that the mass fraction of eutectic point silicon is 11.7% and the eutectic temperature is 577ºC. The maximum solid solubility of silicon in aluminum is 1.65%, and the solid solubility at room temperature is about 0.05%. The eutectic reaction is: according to the silicon content, Al-Si alloy can be divided into subeutectic, eutectic and hypereutectic alloys. There are acicular eutectic silicon and coarse and complex primary silicon in the structure of conventional casting Al-Si alloy, which worsens the properties of the alloy. In industry, modification treatment is used to change the morphology of silicon phase, so that it can be evenly distributed in the matrix with favorable shape and small size, which has a good effect on improving the performance of cast Al-Si alloy. [4]
Methods and effects of metamorphism
There are many kinds of elements, such as Na, Sr, Ba, Bi, Sb and rare earth element Ce, which can affect the metamorphism of eutectic silicon in Al-Si alloy. Among them, Na is the most significant metamorphism and the most widely used in production. In recent years, Sr metamorphism has also been gradually applied in production.
When the liquid aluminum is treated with a complex salt modifier containing sodium fluoride (e.g., ωN&#;F=45%, ωN&#;Cl=40%, ωKCl=15%) or AI-Sr alloy is added to the liquid aluminum, When the residual Na is ωNa 0.001%-0.003% or Sr is ωSr= 0.01%-0.03%, good metamorphic effect can be obtained, and the eutectic silicon in the alloy structure becomes fibrous, which significantly improves the strength and plasticity of the alloy.
The modification process not only changes the silicon crystal structure but also changes the eutectic degree of the alloy. The Na modification process will make the eutectic point shift to the right, even if the eutectic silicon content increases. Therefore, when the alloy is eutectic composition before treatment, it will become subeutectic composition after treatment.
The modification treatment is widely used in the production of cast aluminum alloy. In fact, the ωSi=5~11% aluminum-silicon alloy is carried out within the crystal composition range. With the increase of the silicon content of the alloy, the modification effect is more significant, and the pre-modification treatment has more significant effect in improving the plasticity of the alloy than in improving the strength.
The effect of metamorphic treatment is also related to the crystallization subcooling degree of the alloy (cooling rate of the casting). The thicker the casting wall, that is, the slower the cooling, the smaller the effect of metamorphic treatment. This is known as the wall thickness sensitivity of metamorphic treatment. Similarly, the effect of metamorphic treatment is more significant in metal mold casting than in sand mold casting. The sensitivity of wall thickness varies with different metamorphic elements. When Na or Sr is used for modification, the sensitivity of wall thickness is small, while when Sb or Bi is used for modification, the sensitivity of wall thickness is larger, that is, only in thin wall castings or in metal mold casting conditions, there is a significant metamorphism effect.
The metamorphic effect of aluminum-silicon alloy will disappear gradually with the extension of the time after treatment. This is similar to the phenomenon of breeding decay in cast iron. The deterioration of metamorphic effect is caused by the gradual decrease of the residual amount of metamorphic elements with the extension of time. At the temperature of liquid aluminum, the Na or Sr contained in the alloy is either oxidized or destroyed by the action of water in the molding sand, and the rate of disappearance is to some extent related to the chemical activity of the metamorphic elements. In addition, the melting point and relative density of metamorphic elements also affect the vanishing rate. From the perspective of the effective time of metamorphism, Na has the shortest effective time of 30-60min, Sr 6-7h, Ba more than 5h and Sb more than 100h, while Te can maintain its metamorphism almost indefinitely, and no metamorphic decay occurs even after the alloy is remelted.
Although the effective time of sodium metamorphism is short, it will bring inconvenience to production, but its metamorphic effect is the strongest, so it is still widely used in production. Sr has strong metamorphism and long metamorphism. Effective time, but Sr is expensive, and Sr deterioration will increase the suction of the alloy, so it can not replace Na at present.
The aluminum-based master alloy is made of aluminum as the matrix, and some metal elements with high melting temperature are melted into aluminum to form new alloy materials with specific functions. It can not only greatly improve the comprehensive performance of metals, expand the application field of metals, but also reduce manufacturing costs.
The processing and forming of most aluminum materials requires the addition of aluminum-based master alloys to the primary aluminum to adjust the composition of the aluminum melt. The melting temperature of the aluminum-based master alloy is significantly reduced, so that some metal elements with higher melting temperatures are added to the molten aluminum at a lower temperature to adjust the element content of the melt.
ONE WORLD can provide aluminum-titanium alloy, aluminum-rare earth alloy, aluminum-boron alloy, aluminum-strontium alloy, aluminum-zirconium alloy, aluminum-silicon alloy, aluminum-manganese alloy, aluminum-iron alloy, aluminum-copper alloy, aluminum-chromium alloy and aluminum-beryllium alloy. The aluminum-based master alloy is mainly used in the field of aluminum deep processing in the middle reaches of the aluminum alloy industry.
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