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Vacuum Heat Treatment Furnace

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Aluminum Vacuum Heat Treating

The vacuum quenching, aging and vacuum annealing of aluminum alloy vacuum heat treatment mainly depend on the content and proportion of alloying elements. As the temperature increases, the solubility of copper in lead also increases, forming an α solid solution, which has low strength and high plasticity. Copper can also form CuAl₂ with aluminum, that is, the θ phase compound, which is brittle and hard. If CuAl₂ is not precipitated in time by rapid cooling, an aluminum alloy in a supersaturated α solid solution phase can be obtained, which can be cold-pressed and formed. The supersaturated α solid solution is an extremely unstable organization, and copper atoms can gather in the solid solution at room temperature. The character is seriously distorted, and the strength and hardness of the alloy are improved from the surface. During artificial aging, it is heated to 150~200°C, and the θ’ particle phase is formed at the place where copper atoms gather. During the continuous formation process, the solid solution lattice is distorted and aged.

Due to the small maximum solubility of the added alloy elements, some aluminum alloys have little change in solubility with temperature. If the added alloy content is small, no supersaturated solid solution can be obtained after heating and quenching, so that the alloy cannot be heat treated and aged. In short, the vacuum quenching and aging of aluminum alloys are related to the maximum solubility and content of alloying elements.

Vacuum quenching heat treatment process

The process of dissolving the alloy elements into the α solid solution at the vacuum quenching temperature and rapidly cooling it to fix it is called vacuum quenching. And the most important thing is to soften the alloy, which is convenient for cold forming during the incubation period, and prepares for the metallographic structure in order to improve the comprehensive properties such as strength and hardness. The quality of vacuum quenching has a great influence on performance, and the following factors are the main reasons for endangering quality.

Factors Affecting Vacuum Heat Treatment

(1) Vacuum quenching temperature

The amount of the strengthening phase dissolved into the α solid solution in the alloy is proportional to the temperature. Although increasing the temperature can improve efficiency, save energy, and save working hours. However, because the aluminum alloy vacuum quenching area is narrow and small, it will overheat and even be scrapped if you are not careful. Therefore, the furnace temperature must be strictly controlled.

(2) Vacuum heat treatment time

The amount of excess phase fully dissolved into solid solution is related to the length of holding time. If the holding time is too long, it will not only waste energy, but also the grains will be coarsened and over-burned; on the contrary, if the holding time is too short, the solid solution will not be sufficient, which will lead to low strength after aging. Therefore, it should be based on the effective degree, shape and vacuum quenching of the parts. Depends on the previous state. Generally, for the forged aluminum alloy, due to the large grain size and the slow dissolution of the α solid solution of the excess phase, the holding time should be longer than that of the cold deformed aluminum alloy. The holding time is also related to the heating equipment, medium & heat conduction method used.

(3) Vacuum heat treatment cooling speed

The cooling rate is the guarantee to ensure that gold does not precipitate excess phases from the solid solution, which is proportional to the alloy performance and corrosion resistance, but too fast cooling rate will generate stress and cause parts to deform. Generally, the water temperature should be 30~40℃, and it should be clean and free of oil and corrosive substances, so as not to affect the performance and cooling rate.

Another important factor that affects the quality is the transfer time between the parts coming out of the furnace and entering the water, which is also the key to preventing the precipitation of excess phases to obtain α solid solutions, generally less than 20s is appropriate.

(4) Loading capacity

Parts are not allowed to be piled up or overloaded, and the distance from the furnace wire should be greater than 80mm, and the parts should be placed on the bracket for heating to prevent the temperature of the furnace bottom from being too high. In order to prevent the deformation of the parts when they come out of the oven, the method of binding and hanging fixtures should be considered to ensure the quality.

(5) Vacuum heat treatment medium

There are two kinds of vacuum heat treatment medium, heating and cooling medium. The former includes an air medium for recrystallization or solid solution formation and a medium for heating in nitrates. The latter is used for vacuum quenching and vacuum annealing of alloys, generally using clean tap water at 30-40°C, or hot water heated to 80°C, vacuum quenching medium for cast aluminum, etc.