ã€China Aluminum Industry Network】 Aluminum alloy quenching furnace quenching phase cooling rate must prevent the strengthening phase precipitation quenching of aluminum alloy quenching furnace cooling rate must ensure that the supersaturated solid solution is fixed without decomposition. Prevent the precipitation of strengthening phase and reduce the mechanical properties after quenching aging. Therefore, the faster the cooling rate at quenching, the better. However, the greater the cooling rate, the greater the residual stress and residual deformation of the quenched product. Therefore, the cooling rate must be determined according to different alloys and products of different shapes and sizes.
Generally, the quenching of the alloy is sensitive to the cooling speed, and the selected cooling rate is large. For example, 2A11, 2A12 alloy quenching furnace cooling rate should be above 50 °C / s, and 7A04 alloy is very sensitive to the cooling rate, and its quenching cooling rate is required above 170 °C / s.
For products with different shapes and sizes, different cooling speeds should be used, which is usually achieved by adjusting the temperature of the quenching medium. For the simple shape, small and medium size, bar can be quenched with room temperature water (water temperature is generally l0 ~ 35 °C), for the complex shape, the wall thickness difference between the profiles, available 40 ~ 50 °C water quenching. For products that are particularly susceptible to deformation, the water temperature can even be raised to 75-85°C for quenching. Tests have shown that as the water temperature increases, the mechanical properties and the corrosion resistance of the quenched products are reduced.
Aluminum alloy quenching furnace aluminum alloy more commonly used quenching medium is water. Because of its low viscosity, large heat capacity, rapid heat of evaporation, and strong cooling capacity, it is very convenient and economical to use. However, its disadvantage is that the cooling capacity decreases after heating. Quenching the heated product in water can be divided into three stages: the front stage is the membrane boiling stage. When the hot product is in contact with cold water, a layer of uneven superheated steam film is immediately formed on the surface of the product, which is very firm and has poor thermal conductivity, which reduces the cooling rate of the product. The second stage is the bubble boiling stage. When the steam film breaks, the liquid near the metal surface generates intense boiling and intense heat exchange occurs. The third stage is the convection phase of heat, the circulation of cooling water, or the product swinging around, or moving up and down, increasing the heat exchange between the surface of the product and water convection to increase the cooling rate.
According to the above analysis, in order to quickly break through the previous stage, step by step cooling, to ensure uniform quenching quenching products quenching furnace, quenched tanks need to be equipped with compressed air pipe in order to stir, while the product into the sink to make the appropriate swing. In addition, in order to ensure that the water temperature does not increase too much, the quench tank should have sufficient capacity (generally more than 20 times the total volume of the quenched product). And the cooling water should have a circulation device.
In addition to adjusting the water temperature to control the quench cooling rate of the aluminum alloy quenching furnace, it is also possible to add different solvents to the cooling water to regulate the cooling capacity of the water. An aqueous polyethanol solution is generally used as the cooling medium, and the concentration of the aqueous polyethanol solution can also be adjusted to control the quenching rate of the product. Generally deformable products are often quenched with this aqueous solution of polyethyl alcohol.
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