Depending on alloying elements and heat treatment, aluminum grades can exhibit a wide variety of properties, from good appearance, ease of fabrication, good corrosion resistance, to high strength-to-weight ratio, good weldability and high fracture toughness.
Selection of the proper aluminum grade ultimately depends on the application needed and working conditions.
Aluminum Grades Series 1xxx
These grades of aluminum (1050, 1060, 1100, 1145, 1200, 1230, 1350 etc.) are characterized by excellent corrosion resistance, high thermal and electrical conductivities, low mechanical properties, and excellent workability. Moderate increases in strength may be obtained by strain hardening. Iron and silicon are the major impurities.
Aluminum Grades Series 2xxx
These aluminum alloys (2011, 2014, 2017, 2018, 2124, 2219, 2319, 201.0; 203.0; 206.0; 224.0; 242.0 etc.) require solution heat treatment to obtain optimum properties; in the solution heat-treated condition, mechanical properties are similar to, and sometimes exceed, those of low-carbon steel. In some instances, precipitation heat treatment (aging) is employed to further increase mechanical properties. This treatment increases yield strength, with attendant loss in elongation; its effect on tensile strength is not as great.
The aluminum alloys in the 2xxx series do not have as good corrosion resistance as most other aluminum alloys, and under certain conditions they may be subject to intergranular corrosion. Aluminum grades in the 2xxx series are good for parts requiring good strength at temperatures up to 150°C (300°F). Except for the grade 2219, these aluminum alloys have limited weldability, but some alloys in this series have superior machinability. Aluminum grade 2024 is the most popular alloy and is commonly used in aircraft construction.
Aluminum Grades Series 3xxx
These aluminum alloys (3003, 3004, 3105, 383.0; 385.0; A360; 390.0) generally are non-heat treatable but have about 20% more strength than 1xxx series aluminum alloys. Because only a limited percentage of manganese (up to about 1.5%) can be effectively added to aluminum, manganese is used as a major element in only a few alloys.
Aluminum Grades Series 4xxx
The major alloying element in 4xxx series alloys (4032, 4043, 4145, 4643 etc.) is silicon, which can be added in sufficient quantities (up to 12%) to cause substantial lowering of 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 that of the base metal is required. The aluminum alloys containing appreciable amounts of silicon become dark gray to charcoal when anodic oxide finishes are applied and hence are in demand for architectural applications.
Aluminum Grades Series 5xxx
The major alloying element is magnesium; when it is used as a major alloying element or with manganese, the result is a moderate-to-high-strength work-hardenable alloy. Magnesium is considerably more effective than manganese as a hardener – about 0.8% Mg being equal to 1.25% Mn – and it can be added in considerably higher quantities. Aluminum alloys in this series (5005, 5052, 5083, 5086, etc.) possess good welding characteristics and relatively good resistance to corrosion in marine atmospheres. However, limitations should be placed on the amount of cold work and the operating temperatures (150°F) permissible for the higher-magnesium aluminum alloys to avoid susceptibility to stress-corrosion cracking.
Aluminum Grades Series 6xxx
Aluminum alloys in the 6xxx series (6061, 6063) contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, 6xxx series aluminum alloys have good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength. Aluminum grades in this heat-treatable group may be formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment.
Aluminum Grades Series 7xxx
Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series aluminum alloys (7075, 7050, 7049, 710.0; 711.0 etc.), and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to very high strength. Usually other elements, such as copper and chromium, are also added in small quantities. 7xxx series alloys are used in airframe structures, mobile equipment, and other highly stressed parts. Higher strength 7xxx aluminum alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in a slightly overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness.
Aluminum Grades Series 8xxx
The 8xxx series (8006; 8111; 8079; 850.0; 851.0; 852.0) is reserved for alloying elements other than those used for series 2xxx to 7xxx. Iron and nickel are used to increase strength without significant loss in electrical conductivity, and so are useful in such conductor alloys as 8017. Aluminum-lithium alloy 8090, which has exceptionally high strength and stiffness, was developed for aerospace applications. Aluminum alloys in the 8000 series correspond to Unified Numbering System A98XXX etc.
Aluminum Grades Series 9xxx
This series is not currently used.