Relationship between Casting Process of Aluminum Alloy and Quality of Ingot

Casting process parameters mainly include casting temperature, casting speed and cooling intensity, followed by the height of the liquid level, casting start and end conditions.

1. Casting Temperature Casting bristling usually refers to the temperature required for liquid metal to have good fluidity during injection from a holding furnace through a transfer tool. However, at present, most of the cast aluminum alloys have been applied with on-line degassing and filtration devices, and the casting temperature is still not comprehensive and correct according to the above concept. Practice has proved that the effect of outgassing is different for different liquid temperatures in the on-line degassing device. Therefore, it is necessary to consider the degassing effect of the on-line degassing device for the liquid temperature requirement. In addition, the gas precipitation in the crystallizer should also be taken into consideration. Because the casting temperature is low, the gas in the liquid crystal in the crystallizer will not float up and out of the liquid surface, resulting in porosity, looseness, and may generate slag and cold isolator ingots. The quality defect and casting temperature should not exceed the smelting temperature. Excessive casting temperatures can cause aluminum to leak at the start of casting. Bottom cracks and cracks, may also produce feathers tissue defects, and because the length of the injection tool and the liquid temperature drop is different, there is a heating point on the line head, the liquid temperature fluctuations during the injection process, so the scientific specification of casting temperature should refer to The temperature of the liquid injected into the crystallizer is generally 50?°C~70?°C higher than the actual crystallization temperature of the alloy. The 1xxx, 3xxx aluminum alloy has a narrower transition zone during casting and the casting temperature should be higher; and 2xxx, The transition zone of the 7xxx alloy is wider. The casting temperature should be lower.

2. Casting speed In continuous casting, the length of the ingot formed per unit time is called the casting speed. Old-fashioned casting is usually a casting timea€”a fixed casting speed; whereas modern casting is a curved casting speed, that is, the casting start and the casting process are not the same casting speed: the casting speed is fast and slow to the crack of the ingot, the surface quality of the ingot, The microstructure and properties of the ingot have a great influence. The highest casting speed should be used under the premise of ensuring the quality of the ingot. The old-fashioned casting method solves the crack problem of some alloys and specification ingots, and uses the bottoming or tempering process for casting; whereas the modern casting method adopts the curve ingot casting speed instead of the old-fashioned foundry bottom coating or tempering process. The number of auxiliary facilities has been reduced, manpower has been saved, and labor intensity has been reduced. It is also possible to avoid the fact that the casting speed of some ingot surface defects depends on the characteristics of the alloy produced and the size of the cross-section of the ingot. The general rules for alloys and ingots with a greater tendency to cold cracks should increase the casting speed. For alloys and ingots with a higher tendency to hot cracks, the casting speed should be reduced. 3 Cooling strength The cooling strength is also known as the cooling rate. The cooling strength not only affects the crack of the ingot, but also has a greater influence on the microstructure of the ingot. As the cooling intensity increases, the crystallization speed of the ingot increases, and the intragranular structure becomes more refined; as the cooling intensity increases, casting Acupuncture points become shallow. The reduction of the size of the transition zone makes the metal feeding conditions improve, reducing or eliminating the defects such as porosity and porosity in the ingot. The density of the ingot increases: In addition, the size of the compound can be refined to reduce the degree of regional segregation. .

Old-fashioned casting uses split molds, especially when casting flat ingots. The water jacket is separate from the crystallizer. With the development of casting process technology, the molds of modern casting methods are one. Cooling water is consumed when casting with an old mold, because the old mold water supply is not closed, part of the cooling water is opened and the cooling effect is not achieved, and the difference in cooling intensity between the primary cooling and the secondary cooling is unavoidable. Some ingot quality defects; while casting with a modern crystallizer, the cooling water consumption is small. Practice has proved that it is only about 70% of the old crystallizer water consumption. At present, most foreign countries use low-level crystallizer for casting, the purpose of which is to increase the cooling intensity, reduce or eliminate the heating phenomenon in the air-gap zone after primary cooling, so there is almost no secondary cooling quenching, and ordinary castings of flat ingots have been crystallized. The height of the device is reduced to 100 people, of course, this requires the operator to have a high level of operation or increase the level of white moving control system.

However, the cooling water temperature requirement is not negligible. Normally, the cooling water temperature is set to 20, but due to the regional climatic conditions. The conditions of the water supply facilities and the temperature of the factory buildings lead to large changes, resulting in regional or seasonal ingot quality defects. Modern mold water supply system with pulse or cross-phase function is determined by process programming, so the cooling intensity can be set as a curve according to the casting process needs, especially for some hard alloys with poor low temperature plasticity, cold cracking during casting and Hot cracks are almost present at the same time. With an additional water-retaining plate system, the surface temperature of the ingot is increased to the plastic temperature of the tensile deformation, and the cold cracking of the ingot is eliminated. The hot crack prevention measures are then taken to obtain a high-quality ingot. 4 Conclusion Stable The ingot quality is the result of the best combination of casting process parameters, and the best casting process parameters are based on the combination of casting theory and practice. At present, aluminum composite materials are more demanding in terms of performance. Old-fashioned casting process equipment is no longer adapted to the requirements of the development of new technologies, and its transformation can be accelerated to keep up with the times.

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