Aluminum Grades Explained: A Complete Guide to Aluminum Alloy Series and Their Properties

Aluminum Grades Explained: A Complete Guide to Aluminum Alloy Series and Their Properties

Depending on their alloying elements and heat treatment, aluminum grades can display a wide variety of properties. These range from attractive appearance, ease of fabrication, and good corrosion resistance to a high strength-to-weight ratio, good weldability, and high fracture toughness. Ultimately, selecting the proper aluminum grade depends on the intended application and the working conditions it must withstand.

The sections below outline each aluminum alloy series in turn, summarizing the defining characteristics, typical grades, and common uses that guide material selection.

Table 1. Comparison of Different Aluminum Alloy Series

Aluminum Grades Series 1xxx

The 1xxx aluminum grades (1050, 1060, 1100, 1145, 1200, 1230, 1350, and others) are characterized by excellent corrosion resistance, high thermal and electrical conductivity, low mechanical properties, and excellent workability. Moderate increases in strength can be achieved through strain hardening. Iron and silicon are the major impurities in this series.

Aluminum Grades Series 2xxx

The 2xxx aluminum alloys (2011, 2014, 2017, 2018, 2124, 2219, 2319, as well as cast grades such as 201.0, 203.0, 206.0, 224.0, and 242.0) require solution heat treatment to reach their optimum properties. In the solution heat-treated condition, their mechanical properties are similar to—and sometimes exceed—those of low-carbon steel. In some cases, precipitation heat treatment (aging) is applied to raise mechanical properties further. This treatment increases yield strength, though at the cost of some elongation, while its effect on tensile strength is comparatively smaller.

The 2xxx series does not offer corrosion resistance as good as most other aluminum alloys, and under certain conditions these alloys may be subject to intergranular corrosion. Even so, they perform well in parts requiring good strength at temperatures up to 150°C (300°F). With the exception of grade 2219, these alloys have limited weldability, although some offer superior machinability. Aluminum grade 2024 is the most popular alloy in this series and is widely used in aircraft construction.

Aluminum Grades Series 3xxx

The 3xxx aluminum alloys (3003, 3004, 3105, and cast grades such as 383.0, 385.0, A360, and 390.0) are generally non-heat-treatable but offer roughly 20% more strength than the 1xxx series. Because only a limited amount of manganese (up to about 1.5%) can be effectively added to aluminum, manganese serves as the major element in only a few alloys.

Aluminum Grades Series 4xxx

Silicon is the major alloying element in the 4xxx series (4032, 4043, 4145, 4643, and others) and can be added in quantities of up to 12%, substantially lowering the melting range. For this reason, aluminum-silicon alloys are used in welding wire and as brazing alloys for joining aluminum, where a lower melting range than the base metal is required. Alloys containing appreciable amounts of silicon turn dark gray to charcoal when anodic oxide finishes are applied, making them popular for architectural applications.

Aluminum Grades Series 5xxx

Magnesium is the major alloying element in the 5xxx series. When used on its own or together with manganese, it produces a moderate-to-high-strength, work-hardenable alloy. Magnesium is considerably more effective than manganese as a hardener—about 0.8% Mg is equal to 1.25% Mn—and it can be added in significantly higher quantities. Aluminum alloys in this series (5005, 5052, 5083, 5086, and others) offer good welding characteristics and relatively good resistance to corrosion in marine atmospheres. However, the amount of cold work and the operating temperature (around 150°F) should be limited for the higher-magnesium alloys to avoid susceptibility to stress-corrosion cracking.

Aluminum Grades Series 6xxx

The 6xxx aluminum alloys (6061, 6063) contain silicon and magnesium in roughly the proportions needed to form magnesium silicide (Mg₂Si), which makes them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, the 6xxx series offers good formability, weldability, machinability, and relatively good corrosion resistance, along with medium strength. Grades in this heat-treatable group can be formed in the T4 temper (solution heat treated but not precipitation heat treated) and then strengthened after forming to full T6 properties through precipitation heat treatment.

Aluminum Grades Series 7xxx

Zinc, in amounts of 1 to 8%, is the major alloying element in the 7xxx series (7075, 7050, 7049, and cast grades such as 710.0 and 711.0). When combined with a smaller percentage of magnesium, the result is a heat-treatable alloy of moderate to very high strength. Other elements, such as copper and chromium, are usually added in small quantities as well. The 7xxx series is used in airframe structures, mobile equipment, and other highly stressed parts. Higher-strength 7xxx alloys show reduced resistance to stress-corrosion cracking and are therefore often used in a slightly overaged temper to achieve a better balance of strength, corrosion resistance, and fracture toughness.

Aluminum Grades Series 8xxx

The 8xxx series (8006, 8111, 8079, and cast grades such as 850.0, 851.0, and 852.0) is reserved for alloying elements other than those used in the 2xxx through 7xxx series. Iron and nickel increase strength without significant loss in electrical conductivity, which makes them useful in conductor alloys such as 8017. Aluminum-lithium alloy 8090, notable for its exceptionally high strength and stiffness, was developed for aerospace applications. Alloys in the 8000 series correspond to Unified Numbering System designations such as A98XXX.

Aluminum Grades Series 9xxx

The 9xxx series is not currently in use.