Common Extruded Aluminum Alloys and Their Characteristics

Extruded aluminum alloys can be classified based on the following main characteristics:

(1) According to tensile strength, they are divided into: low strength (< 294 MPa), medium strength (294 – 441 MPa), and high strength (> 441 MPa) aluminum alloys:

(2) According to the degree of heat treatment strengthening, they are divided into: heat-treated strengthened aluminum alloys and non-heat-treated strengthened aluminum alloys;

(3) According to welding performance, they are classified as: weldable aluminum alloys, which can maintain or only slightly change their mechanical properties during melting welding; and non-weldable aluminum alloys, which have significantly reduced strength properties during melting welding.

(4) According to corrosion resistance performance, they are classified as: high corrosion resistance (high general corrosion resistance and stress corrosion resistance in atmospheric conditions and in seawater), medium corrosion resistance, and resistant corrosion aluminum alloys.

The above classification methods are largely conditional because certain alloys can be classified into different types depending on the deformation conditions and heat treatment procedures. For example, the semi-finished product of 2A12 alloy after one-time extrusion, after quenching and natural aging, should maintain the unrecrystallized structure and has a strength greater than 441 MPa, belonging to high-strength aluminum alloys. However, the 2A12 alloy produced by secondary extrusion or by rolling method has a completely or partially recrystallized structure, and its tensile strength is lower than 441 MPa, belonging to medium-strength alloys. The semi-finished product of 6A02 alloy after quenching and artificial aging, its tensile strength is higher than 294 MPa, belonging to medium-strength alloys; while after quenching and natural aging, its tensile strength is lower than 294 MPa, belonging to low-strength aluminum alloys.

Low-strength aluminum alloys (industrial pure aluminum, 3A21, 5005, 5A02, 5A03, 5086) do not undergo strengthening after heat treatment, and their semi-finished products are used in annealed state and after cold hardening. Some aluminum-magnesium-silicon alloys, such as 6063, 6061, also belong to low-strength aluminum alloys. However, these alloys can be strengthened after heat treatment, and their profiles are used after quenching and artificial aging or natural aging. These alloys have good weldability and high corrosion resistance. When these alloys are welded under cold hardening conditions, the strength of the weld seam and the area near the weld seam significantly decreases. Therefore, for the manufacture of structures with the same strength, the wall plate part of the weld zone should be thickened.

Medium-strength alloys can be divided into two groups: non-heat-treated strengthening alloys (5A05, 5A06, 5B06, etc.) and heat-treated strengthening aluminum alloys (6A02, 2A11, 2A70, 2A06, etc.). The semi-finished products of the first group are only used in the annealed state and have good weldability and high corrosion resistance. The semi-finished products of the second group are used after quenching and natural aging or artificial aging. The corrosion resistance and weldability of this group of alloys are different. The 2A02 alloy belongs to high corrosion resistance and weldability alloys, while the 2A11 alloy has lower corrosion resistance and weldability.

High-strength aluminum alloys 7A04 and 2A12 can be sharply strengthened during heat treatment. The semi-finished products of 7A04 alloy are used after quenching and artificial aging, while the semi-finished products of 2A12 alloy are usually used after quenching and natural aging or artificial aging. These alloys have low corrosion resistance and must adopt special protection methods (aluminum coating, anodizing, painting layer). The general corrosion resistance of 7A04 alloy is slightly higher than that of 2A12 alloy, but the corrosion resistance and weldability of 2A12 alloy are lower.

When welding heat-treated strengthening aluminum alloys, the strength of the weld seam and the area near the weld seam significantly decreases, and the corrosion resistance also declines. Therefore, these alloys belong to non-weldable. The assembly of these alloys for manufacturing structures with the same strength generally adopts riveting methods, and rarely uses bolt connections.

Alloy 7A04, 2A12, and 2A06 are mainly used to manufacture wall plates required for load-bearing structures.

Structures made of alloy 7A04 can work for a long time at temperatures not exceeding 100°C. For example: the skin of aircraft, spars, frames, large beams, load-bearing frameworks used in construction, the frame and floor of heavy-duty trucks, the skeleton and floor of train carriages, etc.

Using 2A06 alloy, profiles and structural components that can operate at temperatures ranging from 150 to 250 degrees Celsius can be manufactured. The large profiles and panels of 2A06 alloy, unlike 2A12 alloy, do not exhibit intergranular corrosion or corrosion cracking under the conditions of quenching and natural aging.

2A06 alloy can be used to manufacture the skins, beams, frames and other structural parts of aircraft that are subjected to intense heating during use.

2A70, 2A50, 5A05, and 5A06 alloys are mainly used to manufacture the walls of structures that bear moderate loads. 2A70 and 2A50 alloys are used after quenching and artificial aging, while 5A05 and 5A06 alloys are used after annealing. These alloys can be used to manufacture the frames of train carriages and bodies, welded fuel tanks, load-bearing suspended ceilings and partitions in buildings, ship decks, and other structures.

Using 6A02 and 6063 alloys that have undergone quenching and natural aging can produce decorative panels and civil building structures. These alloys have high corrosion resistance and can be well polished and anodized. Additionally, in certain cases, 5A06 and 5A03 alloys can also be used to manufacture civil building structures.

In some cases, 1035 industrial pure aluminum and 3A21 alloy panels can be used to manufacture decorative components for building structures.