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Vacuum Heat Treatment Furnace

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Understand the advantages of vacuum heat treatment of aluminum alloys

The quenching of aluminum alloys is also called solid solution treatment, that is, through high-temperature heating, as many alloying elements existing in the form of the second phase in the metal are dissolved into the solid solution as possible, and then rapidly cooled to suppress the precipitation of the second phase, thereby obtaining a A supersaturated aluminum-based α solid solution is prepared to prepare the structure for the next step of aging treatment.

Vacuum quenching is the most important and most demanding heat treatment operation for aluminum alloys. The key is to select the appropriate vacuum quenching heating temperature and ensure a sufficient vacuum quenching cooling rate, and to strictly control the furnace temperature to reduce quenching deformation.

The principle for selecting the vacuum quenching temperature is to increase the quenching heating temperature as much as possible while ensuring that the aluminum alloy does not over-burn or the grains grow excessively, so as to increase the supersaturation of the α solid solution and the strength after aging treatment. Generally, aluminum alloy heating furnaces require furnace temperature control accuracy within ±3°C, and at the same time, the air in the furnace is forced to circulate to ensure the uniformity of the furnace temperature.

Overburning of aluminum alloys is caused by the local melting of low-melting-point components within the metal, such as binary or multi-element eutectics. Over-burning not only reduces the mechanical properties, but also has a serious impact on the corrosion resistance of the alloy. Therefore, once overburning occurs in aluminum alloys, it cannot be eliminated, and alloy products should be scrapped. The actual over-burning temperature of aluminum alloys mainly depends on the alloy composition and impurity content, and is also related to the processing state of the alloy. The over-burning temperature of products processed by plastic deformation is higher than that of castings. The greater the amount of deformation processing, the more non-equilibrium low melting point compositions. It becomes easier to dissolve into the matrix when heated, so the actual overburning temperature increases.

The cooling rate during vacuum quenching of aluminum alloys has a significant impact on the aging strengthening ability and corrosion resistance of the alloy. During the quenching process of LY12 and LC4, it must be ensured that the α solid solution does not decompose, especially in the temperature sensitive area of 290~420°C, there must be enough Great cooling rate. It is usually stipulated that the cooling rate should be above 50℃/s, and for LC4 alloy, it should reach or exceed 170℃/s.

The most commonly used quenching medium for aluminum alloys is water. Production practice shows that the greater the cooling rate during quenching, the greater the residual stress and residual deformation of the quenched material or workpiece. Therefore, for small workpieces with simple shapes, the water temperature can be slightly lower, generally 10~30℃, and should not exceed 40℃. For workpieces with complex shapes and widely varying wall thicknesses, in order to reduce quenching deformation and cracking, the water temperature can sometimes be increased to 80°C. However, it must be pointed out that as the water temperature of the quenching tank increases, generally speaking, the strength and corrosion resistance of the material also decrease accordingly.