Aluminum alloy and aluminum temper designations

1.Aluminum alloy features

The density of aluminum is 2.7 g/cm³, which is about 1/3 of that of steel (7.8 g/cm³). Substituting aluminum alloy for steel can reduce weight by about 50%. Since the surface of aluminum is easily oxidized to form a dense and stable oxide film (passivation), it has good corrosion resistance. Aluminum has better castability, because aluminum has a low melting temperature and good fluidity, making it easy to manufacture parts with various complex shapes.So aluminum extrusion is possible. Aluminum is formed by adding one or several elements to aluminum, which can increase strength and hardness compared to pure aluminum. In addition to solid solution strengthening, some aluminum alloys can also be strengthened by heat treatment, so that the tensile strength exceeds 600 MPa. Aluminum alloys are widely used in radiator in car.

Table 1 Advantages of aluminum alloy

Nb.#Main advantagesdescription
1Low density 1/3 of steel
2Good corrosion resistanceCombined with Zn, it can form long-life aluminum that is not easy to corrode.
3Flexible strength designThe strength at room temperature is not lower than that of cast iron
4Beautiful surfaceColorless and transparent oxide film
5Good machining performanceLow melting temperature, easy to cast into complex shapes; good cutting performance,aluminum alloy is widely used in CNC machining

2.Pure aluminum and aluminum alloy series

The series of aluminum alloys are divided into nine series from 1000 to 9000 according to the types and contents of non-aluminum elements contained. We generally use 3 series and 6 series aluminum alloys for extrusion processing.

Table 2 aluminum alloy series

Pure aluminum (aluminum content is not less than 99.00%)1×××
Aluminum alloy with copper as the main alloying element2×××
Aluminum alloy with manganese as the main alloying element3×××
Aluminum alloy with silicon as the main alloying element4×××
Aluminum alloy with magnesium as the main alloying element5×××
Aluminum alloy with magnesium and silicon as the main alloying elements and Mg2Si phase as the strengthening phase6×××
Aluminum alloy with zinc as the main alloying element7×××
Aluminum alloy with other alloying elements as the main alloying elements8×××
Spare alloy group9×××

3.Aluminum alloy base code

The basic principle of naming deformed aluminum and aluminum alloy state code: the basic state code is represented by an English capital letter; the subdivision state code is represented by the basic state code followed by one or more Arabic numerals.

Table 3 Basic code of aluminum alloy

CodenamenameDescription and application
FFree processing stateIt is suitable for products with special requirements for work hardening and heat treatment conditions during the molding process. The mechanical properties of the products in this state are not regulated.
OAnnealed stateSuitable for processed products that have been fully annealed to obtain the lowest strength.
HWork hardened stateIt is suitable for products whose strength is increased by work hardening. After work hardening, the product can undergo (or not) additional heat treatment (generally non-heat-treated reinforced materials) to reduce the strength. The state code behind the non-heat-treated strengthened aluminum alloy is generally the letter H plus three digits.For example,H112.
THeat treatment state(Different from F, O, H state) It is suitable for products that are stable after (or without) work hardening after heat treatment. The T code must be followed by one or more Arabic numerals (usually heat treatment strengthened materials).For example,T5.

4.Aluminum and aluminum alloy heat treatment classification

4.1 Annealing

After the product is heated to a certain temperature and kept for a certain period of time, it is cooled to room temperature at a certain cooling rate. Through the diffusion and migration of atoms, the organization is made more uniform and stable, and the internal stress is eliminated, which can greatly improve the plasticity of the material, but the strength will be reduced. For a more precise answer, please refer to Wikipedia Annealing.

4.2 Solution quenching treatment

Heat the heat-treatable and strengthened aluminum alloy material to a higher temperature and keep it for a certain period of time, so that the second phase or other soluble components in the material are fully dissolved into the aluminum matrix to form a supersaturated solid solution, and then use a rapid cooling method Keep this supersaturated solid solution at room temperature, it is an unstable state, because it is in a high-energy state, solute atoms may precipitate out at any time. However, at this time, the plasticity of the material is relatively high, and cold working or straightening procedures can be carried out. For a more precise answer, please refer to Wikipedia solution quenching.

4.3 Aging treatment

After solution quenching, the material is kept at room temperature or higher temperature for a period of time, the unstable supersaturated solid solution will be decomposed, and the second phase particles will be precipitated (or precipitate) from the supersaturated solid solution and distributed around the aluminum grains. The strengthening effect is called precipitation strengthening. For a more precise answer, please refer to Wikipedia Aging treatment.

4.4 Retrogression and raging

After aging-strengthened, the aging alloy is heated at a certain temperature below the equilibrium phase or the solid solubility of the phase, the aging disappears will immediately disappear, and the original state will return to the fixed state. This kind of regression treatment occurs in this alloy. After the return, aging can be carried out again, and the regenerative hardening can still be carried out, but the aging speed will slow down, and the rest will not change much.For a more precise answer, please refer to Wikipedia retrogression and raging.

For different application requirements,such as forming,brazing quality and corrosion resistance,Aluminum alloys are selected by different temper state to balance these requirements.When the temper is defined,its production process is decided.

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