The Types Of Aluminum And Aluminum Alloys

Pure aluminum

The characteristic of pure aluminum is its low density, which is 2.72g/cm ³, only about one-third of the density of iron or copper. Good conductivity and thermal conductivity, second only to silver and copper. The chemical properties of aluminum are very active.

In the air, the surface of aluminum can combine with oxygen to form a dense Al2O3 protective film, which prevents further oxidation of aluminum. Therefore, aluminum has good corrosion resistance in air and water, but it cannot resist acid, alkali, and salt corrosion.

Aluminum has a face centered cubic lattice and good plasticity (δ=50%, ψ=80%). It can be processed into profiles such as wires, plates, strips, and pipes through cold or hot pressure, but its strength is not high, σb＝80MPa， After cold processing, σb＝(150～250)MPa。 So pure aluminum is mainly used to make wires, cables, heat sinks, and daily necessities or alloys that require rust and corrosion resistance but low strength requirements.

Commercial purity aluminum is not as pure as chemical purity aluminum, as it contains impurities such as Fe, Si, etc. to varying degrees. The more impurities are present in aluminum, the lower its conductivity, thermal conductivity, resistance to atmospheric corrosion, and plasticity.

The grades of industrial pure aluminum in our country are formulated based on the limit of impurities, such as L1 L2、L3……。 L is the first Chinese Pinyin character for “aluminum”, and the higher the sequence number attached after it, the lower its purity.

Aluminum alloy

Pure aluminum has low strength and is not suitable as a structural material. To improve its strength, the most effective method is to add alloying elements such as Si, Cu, Mg, Mn, etc. to make aluminum alloy (aerolite). These aluminum alloys have high strength, but still have low density, especially high specific strength (i.e. the ratio of strength limit to density), as well as good thermal conductivity and corrosion resistance.

Classification of Aluminum Alloys

According to the composition and production process characteristics of aluminum alloys, they can be divided into two categories: deformed aluminum alloys and cast aluminum alloys.
When the composition of the alloy is less than D/point, it can form a single-phase solid solution structure when heated, with good plasticity and suitable for pressure processing, hence it is called deformed aluminum alloy.

Aluminum alloys with a composition smaller than the F-point in deformation, whose solid solution composition does not change with temperature and cannot be strengthened by heat treatment, are called heat treatment unreinforced aluminum alloys; An alloy with a composition between F and D/, whose solid solution composition changes with temperature, can be strengthened by heat treatment, hence it is called an aluminum alloy that can be strengthened by heat treatment.

Alloys with a composition greater than D/point, low melting point eutectic structure, good flowability, suitable for casting, are called cast aluminum alloys, but not suitable for pressure processing.

Deformable aluminum alloys can also be classified into rust proof aluminum, hard aluminum, ultra hard aluminum, and forged aluminum according to their main performance characteristics.
Casting aluminum alloys can also be classified according to the different main alloying elements: Al Si, Al Cu, Al Mg, Al Zn, etc.

Heat treatment characteristics of aluminum alloy

Aluminum alloys can not only improve their strength through cold deformation work hardening, but also further enhance their strength through heat treatment – “age hardening” method.
The heat treatment mechanism of aluminum alloy is different from that of steel. After quenching, the hardness and strength of steel immediately increase, while the plasticity decreases. Aluminum alloys with components between F and D/can be heated to the alpha phase region, insulated, and quenched by water cooling to obtain supersaturated alpha solid solutions at room temperature. Their strength and hardness cannot be immediately increased, but their plasticity is significantly improved. This process is called quenching or solution treatment.

Due to the instability of the supersaturated solid solution obtained after quenching, there is a tendency to precipitate a second phase (strengthening phase). After being left at room temperature for a period of time or heated at low temperatures, atoms have the ability to move within the lattice and gradually transition to a stable state, resulting in a significant increase in strength and hardness, while plasticity decreases. The phenomenon of further strengthening of the alloy after solid solution treatment over time is called “age hardening” or “age hardening”. The aging process carried out at room temperature is called natural aging, while the aging process carried out under heating conditions is called artificial aging.

Deformable aluminum alloy

1. Anti rust aluminum alloy

The main alloying elements are Mn and Mg. This type of alloy is a single-phase solid solution after forging and annealing, so it has good corrosion resistance and plasticity. The rust proof aluminum grade is represented by the Chinese Pinyin prefix “LF” followed by a sequential number. Such as LF5, LF11, LF21, etc. This type of alloy is mainly used for rolling, welding, or corrosion-resistant structural components with low loads, such as oil tanks, pipes, wires, light load skeletons, and various household appliances. All kinds of anti rust aluminum alloys are aluminum alloys that cannot be strengthened by heat treatment. To improve the strength of the alloy, cold pressure processing can be applied, which can produce work hardening.

2. Hard aluminum alloy

Duraluminum is basically an Al Cu Mg alloy with a small amount of Mn. Various types of duralumins can be strengthened by aging, but their corrosion resistance is poor, especially in seawater. Therefore, hard aluminum components that require protection are wrapped with high-purity aluminum on the outside to make aluminum coated hard aluminum materials. Hard aluminum grades use the Chinese Pinyin prefix “LY” followed by a sequential number, such as LY1 (rivet hard aluminum), LY11 (standard hard aluminum), and LY12 (high-strength hard aluminum).
Hard aluminum is a structural material with high specific strength, which has been widely used in the aviation industry and instrument manufacturing.

3. Super hard aluminum alloy (SD alloy)

It is an Al Cu Mg Zn alloy, which is made by adding Zn to hard aluminum. This type of alloy is currently the strongest aluminum alloy, with higher specific strength, hence it is called superhard aluminum. The disadvantage is also poor corrosion resistance, which can increase the artificial aging temperature or aluminum coating.
The grade of ultra hard aluminum alloy is represented by the Chinese Pinyin prefix “LC” followed by a sequential number. LC4, LC6, etc. are commonly used to manufacture important components with high stress, such as aircraft beams.

4. Forged aluminum alloy

It is an Al Cu Mg Si alloy with a variety of alloying elements, but the content of each element is relatively low, thus it has good thermoplastic and corrosion resistance, and its strength is comparable to that of hard aluminum. After quenching and aging, the strength can be improved.
The grade of forged aluminum alloy is represented by the Chinese Pinyin prefix “LD” followed by a sequential number, such as LD5, LD7, etc. Due to its excellent forging performance, it is mainly used for forging or forging parts that bear heavy loads on aircraft or diesel locomotives.

Cast aluminum alloy

There are many types of cast aluminum alloys, among which aluminum silicon alloys have good casting performance, sufficient strength, and low density, and are widely used, accounting for more than 50% of the total production of cast aluminum alloys. Al Si alloys containing Si (10-13)% are the most typical aluminum silicon alloys, belonging to eutectic composition, commonly known as “silicon aluminum alloys”.

The grade of cast aluminum alloy is represented by the Chinese Pinyin prefix “Z”+Al+other major element symbols and percentage content of the word “cast”. For example, ZAlSi12 represents cast Al Si alloy containing 12% Si.

The code for the alloy is represented by the Chinese Pinyin prefix “ZL” of “cast aluminum” followed by three digits. The first digit represents the alloy category, while the second and third digits indicate the sequence number of the alloy.

Example ZL102 represents the casting aluminum alloy of Al Si series No. 2.
Casting aluminum alloy is generally used to produce parts that are lightweight, corrosion-resistant, have complex shapes, and have certain mechanical properties. Such as aluminum pistons, instrument housings, water-cooled engine cylinder components, crankcases, etc.