Characteristics and comparison of the five aluminium alloy series

Aluminium alloys are the backbone of modern industry due to their light weight, high strength, easy processing and corrosion resistance. Different combinations of alloying elements have created series with different properties to meet diversified needs. The following is an in-depth analysis and comPArison of the five core aluminium alloy series:

• 2xxx Series (Al-Cu alloys)

——the backbone of the sky, a pioneer in strength and heat resistance

Aluminium alloys of the 2xxx series are based on copper and magnesium as the main added elements. Its most striking feature is its extremely high strength, which, especially after heat treatment (age-hardening), ranks among the strongest of the commonly used aluminium alloys.

At the same time, the series possesses excellent heat resistance and maintains good mechanical properties in higher temperature environments, which gives it an advantage in high-temperature application scenarios.

However, the other side of the coin is that its relatively poor corrosion resistance makes it susceptible to corrosion when exposed to harsh environments, so additional surface protection treatments (e.g. coatings or aluminium cladding) are often required. In terms of joining process, its welding performance is average, and mechanical connections such as riveting are more often used.

Common grades are 2024 and 2219.

• 3xxx Series(Al-Mn alloys)

——guardians of architecture, models of economy and corrosion resistance

The main element added to the 3xxx series is manganese.

The core competence of this series lies in excellent corrosion resistance and excellent forming and processing properties (especially deep-drawn and rolled processes). It has excellent resistance to atmospheric conditions, especially industrial and marine atmospheres, and is easy to machine into a wide range of complex shapes. In addition, it has good welding properties, an excellent surface finish and a relatively low cost.

Its main limitation is that the strength is medium and it is not well suited for use as a primary load-bearing structural member.

Common grades are 3003 and 3105.

• 5xxx Series(Al-Mg alloys)

——the shield of the sea, the benchmark for corrosion resistance and welding

5xxx Seriesuses magnesium as the main alloying element.

The most outstanding advantage of this series is its unrivalled corrosion resistance, especially in salt-containing marine environments as well as in chlorinated environments. It also has excellent weldability, with strong welded joints and good corrosion resistance. Its strength ranges from medium to high (increasing with magnesium content), and it has good work-hardening capacity (strength can be further improved by cold working) and formability.

However, some grades may be sensitive to stress corrosion cracking under certain conditions when the magnesium content is very high.

Common grades are 5052 and 5754.

• 6xxx series (Al-Mg-Si alloys)

——all-rounders, balancers of all-round performance

The main additive elements of the 6xxx series are magnesium and silicon, which form the reinforcing phase Mg2Si.

The most important feature of this series is its excellent balance of properties. It has good medium strength (which can be significantly increased by solution treatment and ageing heat treatment), excellent corrosion resistance (generally better than 2xxx and 7xxx) and excellent extrudability, which makes it ideal for producing profiles with complex cross-sections.

At the same time, it has good welding properties (especially in the T6 heat-treated condition), good machinability, and a surface anodising effect that is very pleasing to the eye. It is not as strong as the 2xxx and 7xxx series, but it is strong enough for many applications.

Common grades are 6061 and 6082.

• 7xxx Series(Al-Zn-Mg-Cu alloys)

——the king of strength, the ultimate load-bearer

The 7xxx series is usually based on zinc and magnesium, sometimes with copper added.

This series is rightly called the ‘king of strength’ among aluminium alloys. It has the highest room-temperature strength of all aluminium alloys, especially when properly heat-treated (aged) to aerospace grade. It also has excellent fracture toughness and can withstand high loads and impacts.

However, the price for the pursuit of extreme strength is relatively average corrosion resistance, especially sensitive to stress corrosion cracking, and in the high-strength state especially need to pay attention to the environment and conditions of use. In addition, its welding properties are poor and the welding process is complex, usually requiring special welding techniques and post-weld treatment.

Common grades are 7075 and 7050.

• A brief comparison of the core features of the five series:

These five aluminium alloy series are like different tools in a material toolbox, each with its own unique edge and best use:

2xxx and 7xxx are the power players, specialising in high strength, heat resistance and extreme load bearing.

3xxx and 5xxx are the corrosion experts, guarding the buildings and oceans.

6xxx is the master of equilibrium, striking the optimal balance between strength, corrosion resistance and workmanship, which is widely used in daily projects.

When selecting materials, it is important to consider multiple factors such as load, corrosive media, temperature, forming process (stamping, extruding, forging), joining method (welding, riveting), and cost budget.