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Aluminum heat treatment is applied in sectors such as aerospace, defense and automotive. The strength of 2XXX, 6XXX, 7XXX and 8XXX series aluminum alloys can be increased by subjecting them to aging (precipitate hardening) heat treatment. Aluminum furnaces can be designed to suit this. The most commonly used furnace model is the aluminum solution and aging furnace.
Aluminum solution and aging furnaces typically require rapid cooling after keeping the material to be aged at the solution temperature for a while. This process, unlike the quenching process applied to steels, is done to protect the alloy taken into solution from hardening. The soft alloy taken into solution must be shaped quickly. Otherwise, it will naturally begin to age and therefore harden under environmental conditions.
The finalized aluminum parts are subjected to the aluminum solution and aging process in the aging furnace. This process is called artificial aging. In some cases, shaped parts can be subjected to natural aging at ambient temperature instead of artificial aging, and various combinations of natural and artificial aging can also be applied to the relevant alloys. The aging process in aluminum solution and aging furnaces typically occurs by heating the parts, holding them for a period of time at temperatures well below the solution temperature, and cooling them to ambient temperature at non-sudden cooling rates.
One of the issues to be considered in aluminum solution and aging furnaces is the way the parts are heated. As it is known, there are 3 types of heating methods. The first of these is radiation. Radiation heating occurs when high-energy rays emitted from resistors come into contact with the parts' surfaces, just like the sun's rays warm our earth. The other heating method is conduction. Conductive heating consists of the conduction of heat in a solid object. Here, heat transmission is achieved from the hot parts of the parts to the cold parts by waves called phonons. This is a situation that occurs in every heat treated part. The last heating method is convection. Heat transfer in the Earth's atmosphere can be achieved by convection-based air currents as well as by radiation. In furnaces containing any gas atmosphere such as air, argon, etc., heating occurs mainly by convection.
The point that should be taken into consideration in aluminum solution and aging furnaces is to prevent the parts from being heated by the radiation emitted from the resistances as much as possible. The designs of aluminum solution and aging furnaces should be based mainly on the convection heating principle. Otherwise, local eutectic melting may occur on the alloy surface, which may affect the service life of the parts. This issue is a situation that needs to be taken into consideration especially during the solution process.
Another important issue in aluminum solution and aging furnaces is the cooling system. The heat transfer rate in the cooling boilers, the temperature of the cooling medium and the liquids used in cooling are important in terms of distortion and size controls of the heat-treated parts during cooling. The design of the parts to be heat treated and the furnace should be consistent, and aluminum solution and aging furnaces should be designed in accordance with the product quality.
In aluminum solution and aging furnaces, temperature changes within the effective working area of the furnace are also important. Accordingly, part designers do not approve heat treatment work areas that exceed a certain temperature fluctuation. Furnace design is of great importance to ensure temperature homogeneity. The circulation regime in the aluminum solution and aging furnace, the size and mass of the parts and the way they are placed in the furnace, the temperature gauges used and their locations, the insulation status of the furnace and the software that provides heating control of the furnace are the main factors affecting temperature homogeneity.
In summary, many details in the design of aluminum solution and aging furnaces, as well as those mentioned above, are important for the health of the heat treatment process. Finishing parts that require great effort to produce with a correct heat treatment process will bring the added value of the products to the desired levels.
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