This article takes an in-depth look at the types of aluminum.
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Aluminum is the most abundant metal on the Earth’s crust, but it rarely exists as an elemental form. Aluminum and its alloys are valued because of their low density and high strength-to-weight ratio, durability, and corrosion resistance. Aluminum is 2.5 times less dense than steel, making it an excellent alternative in applications requiring mobility and portability. Generally, aluminum alloys are highly ductile and malleable; they are easily formed and machined. They are also good electrical and thermal conductors, non-sparking, and non-magnetic. Aluminum materials have many applications in the industry and our everyday living. These materials are highly recyclable, requiring low re-melting energy, which is only 5% of the energy needed to produce the primary metal. Seventy-five percent of the aluminum is recovered for reuse without losing its desirable properties. Hence, aluminum materials are very sustainable.
In the succeeding chapters, we will explore the grades and forms of aluminum alloys and their applications.
Pure aluminum is combined with different alloying elements to modify its mechanical properties, corrosion resistance, and formability, and machinability. This practice results in various aluminum grades available commercially. The Aluminum Association created and is responsible for maintaining the nomenclature for the standard aluminum grades. Aluminum grades are categorized according to their main alloying element and their mechanical and thermal treatment response.
There are two main classifications of aluminum alloys: wrought aluminum and cast aluminum. Both categories have different designation systems.
Wrought aluminum is produced by smelting aluminum ingots together with a specific amount of alloying metals, resulting in the required grade's composition. The smelted aluminum alloy is cast and undergoes mechanical working processes such as rolling, forging, and extrusion.
A four-digit number code identifies each wrought aluminum grade:
The first digit indicates the primary alloying element added to the pure aluminum. The primary alloying element greatly affects the grades' properties in a series.
The second digit refers to the modification of a specific alloy. The modifications are registered with the IADS, which requires specific documentation. If the designated number is zero, the alloy is original or unmodified.
The third and fourth digits are arbitrary numbers assigned to a specific alloy in the series. For the 1000 series, these digits indicate the purity of the alloy.
The table below summarizes the wrought aluminum series. For aluminum 1060, for instance, is made of almost pure aluminum, containing 99.60% aluminum.
| Grade | Primary Alloying Element |
|---|---|
| 1XXX | 99.00% Aluminum (minimum) |
| 2XXX | Copper |
| 3XXX | Manganese |
| 4XXX | Silicon |
| 5XXX | Magnesium |
| 6XXX | Magnesium and Silicon |
| 7XXX | Zinc |
| 8XXX | Other Elements |
The following are the series of wrought aluminum grades:
The 1000 series is non-heat treatable and contains at least 99.0% aluminum with no significant alloying elements. The aluminum grades under this series have excellent corrosion resistance and the highest electrical and thermal conductivities. Due to their ductility and relative softness, they are highly formable and work-hardens very slowly. Hence, they are suitable for processes requiring severe deformation. They are weldable, but their narrow melting range must be considered during the welding. However, these grades have lower mechanical strength.
Aluminum 1100 is the most common grade and highest mechanical strength in the 1000 series. It is commonly known as pure commercial aluminum. This grade has good electrical and thermal conductivity, making them suitable for heat sinks and heat exchange equipment, respectively. This grade has excellent forming properties, making it suitable for coldworking processes such as drawing, bending, spinning, stamping, and roll forming. It has good ductility in the annealed temper condition. It can be formed into wires, plates, foils, bars, and strips. Coldworking is often performed, though hot forming is easily performed this grade. This grade can also be welded easily by conventional welding methods, including resistance welding. However, they are not suitable for high pressure applications. Like most alloys in this series, Aluminum 1100 cannot be hardened by heat treatment and is only hardened by coldworking.
2000 series aluminum grades contain 0.7-6.8% copper and small amounts of silicon, manganese, magnesium, and other elements. Copper is the alloying element for these grades that impart additional strength and hardness, improving their machinability. The high strength of these grades is maintained at a wide range of temperatures.
2000 series aluminum grades are high-performance and high-strength alloys; hence, they are suitable for aircraft and aerospace applications. However, copper addition also decreases the ductility and corrosion resistance.
The 2000 series are heat treatable aluminum grades. Precipitation hardening can be performed to increase their strength. The precipitation of the intermetallic Al2Cu during heat treatment increases the hardness of the alloy. However, the intermetallic compounds can make these grades challenging to weld. Some 2000 series grades are not suitable for arc welding because of their susceptibility to hot cracking and stress corrosion cracking.
Aluminum 2011 is a free-machining alloy. It has excellent machinability properties (i.e., generates small chips and gives a better surface finish), making it suitable for the high-speed lathing process. This grade is a highly versatile alloy. However, it has poor corrosion resistance, which can be solved by coating or anodizing. They are not recommended for forming and welding.
Aluminum 2024 is one of the widely known high-strength aluminum alloys. This alloy has good fracture resistance, fracture toughness, and low fracture crack growth. It is ideal for heavy-duty applications under stress for prolonged periods. However, it also has poor corrosion resistance, which can be mitigated by cladding or anodizing.
3000 series aluminum grades contain 0.05-1.5% manganese, the main alloying element. Manganese gives the alloy higher mechanical strength than pure aluminum, which is maintained at a wide range of temperatures. They have good corrosion resistance, high ductility, and formability. They are non-heat-treatable and can be hardened by cold working. They are suitable for welding.
Aluminum 3003 is the most widely used aluminum grade that contains 1.5% manganese and 0.1% copper. It has the excellent mechanical properties of Aluminum 1100 with 20% higher tensile strength. This grade can be deep drawn, spun, welded, and brazed.
4000 series aluminum grades contain 3.6-13.5% silicon and small amounts of copper and magnesium. Silicon is the main alloying element that lowers the alloy's melting point, resulting in improved fluidity during the molten state. This makes the 4000 series grades good filler material for welding and brazing.
Some grades under the 4000 series are heat treatable depending on the amounts of copper and magnesium in the alloy. Such additions will give a favorable response to heat treatment. The heat-treatable grades can be used for welding if combined with the aluminum grades under a heat-treatable series.
5000 series aluminum grades contain 0.5-5.5% magnesium. These grades are non-heat-treatable and can be hardened by cold working. They have moderate-to-high strengths and high ductility in annealed conditions. They are readily weldable and have high corrosion and alkaline resistance. The grades in this series containing 3.5% magnesium are not suitable for high-temperature applications as they are prone to stress corrosion.
Aluminum 5005 is used in general sheet metal work. This grade has good formability and is easy to bend, spin, draw, stamp, and roll-form. It has good corrosion resistance and can withstand marine environments.
Aluminum 5083 contains traces of manganese and chromium. It is highly resistant to most industrial chemicals and seawater. It retains its high strength after welding.
Aluminum 5052 has the highest strength among the non-heat-treatable aluminum grades. It exhibits good finishing qualities. It offers better resistance to marine environments compared to other aluminum grades. It can be drawn and formed into intricate shapes due to its excellent workability.
6000 series aluminum grades contain 0.2-1.8% silicon and 0.35-1.5% magnesium as the major alloying elements. These grades can be solution heat-treated to increase their yield strength. The precipitation of magnesium-silicide during aging hardens the alloy. A high silicon content enhances precipitation hardening, which can result in reduced ductility. Still, this effect may be reversed by the addition of chromium and manganese, which depresses recrystallization during heat treatment. These grades are challenging to weld because of their sensitivity to solidification cracking, and proper welding techniques must be employed.
Aluminum 6061, also known as the “work-horse” alloy, is the most versatile among the heat treatable aluminum alloys. It has excellent formability (using bending, deep drawing, and stamping) and corrosion resistance. It can be welded using any method, including arc welding.
Aluminum 6063 has high tensile strength and corrosion resistance and excellent finishing qualities. This alloy is commonly used for aluminum extrusion. It is suitable for anodizing because it can produce smooth surfaces after forming intricate shapes. It also has good weldability and average machinability.
Aluminum 6262 is a free-machining alloy that has excellent mechanical strength and good corrosion resistance.
7000 series aluminum grades contain 0.8-8.2% zinc as the primary alloying element. This series comprises some of the highest strength aluminum alloys. The 7000 series grades are heat treatable; solution heat treatment followed by aging can be performed to increase their yield strength. The precipitation of MgZn2 and Mg3Zn3Al2t intermetallic compounds hardens the alloy. The 7000 series grades have high corrosion resistance, which is enhanced by the addition of copper. Most grades in this series are not weldable due to their susceptibility to stress corrosion cracking and hot cracking.
Aluminum 7075 is a high-performance alloy with one of the highest strengths among the aluminum grades. It is harder and has higher tensile strength than Aluminum 6061. It can withstand prolonged periods of stress. It can be welded using spot or fuse methods.
Cast aluminum is produced by a casting process. This process involves pouring molten aluminum, together with specific amounts of the alloying elements, into a mold to form the desired shape of the alloy. Cast aluminum alloys generally have lower tensile strength than wrought aluminum. They are susceptible to cracking and shrinkage. However, they are more cost-effective. These alloys can be formed into a wide variety of shapes because molten aluminum can flexibly take the shape of the mold cavities.
A four-digit code that includes a decimal value is assigned to each cast aluminum grade:
The first digit indicates the primary alloying element of the grade or series.
| Series | Primary Alloying Element |
|---|---|
| 1XX.X | 99.00% Aluminum (minimum) |
| 2XX.X | Copper |
| 3XX.X | Silicon with added copper and/or magnesium |
| 4XX.X | Silicon |
| 5XX.X | Magnesium |
| 7XX.X | Zinc |
| 8XX.X | Tin |
| 9XX.X | Others |
The 6XX.X series is not used.
The second and third digits are arbitrary except for the 1XX.X series. For these series, these digits indicate the purity of the pure aluminum alloy.
The last digit indicates whether the alloy is a casting (“.0”) or an ingot (“.1” or “.2”).
The following are the cast aluminum alloy series:
1XX.X series aluminum grades have high electrical and thermal conductivity, good weldability, and excellent corrosion resistance and finishing properties.
2XX.X series aluminum grades are heat-treatable. They have high strength and low fluidity. However, they have low corrosion resistance and ductility and are susceptible to hot cracking.
3XX.X series aluminum grades are heat-treatable. They have high strength and good wear and cracking resistance. However, the increased copper content can make the grade less resistant to corrosion. They also have lower ductility.
4XX.X series aluminum grades are non-heat-treatable and have moderate strength. They have good machinability due to their high ductility. They also have good impact resistance, corrosion resistance, and casting properties.
5XX.X series aluminum grades are non-heat-treatable. They have good corrosion resistance and a very attractive appearance when anodized. They have moderate-to-high strength, good machinability, and casting properties.
7XX.X series aluminum grades are heat-treatable. They have high strength, good corrosion resistance, good dimensional stability, and good finishing qualities. However, they have poor casting properties.
8XX.X series aluminum grades are non-heat-treatable. They have good machinability and wear resistance due to their low coefficient of friction. However, they have low strength.
The temper designation system is useful in determining the response of a certain alloy to welding and other fabrication processes, which depends on the strengthening and hardening processes it has undergone. This system is used by both wrought and cast aluminum alloys.
The temper designation of an aluminum alloy is composed of a capital letter, followed by a two-digit number for strain hardened and thermally treated alloys. It is separated by a hyphen to the alloy numbering designation (e.g., 5052-H32).
The first character in a temper designation indicates the main classification of treatment.
| Letter | Treatment |
|---|---|
| F | As fabricated alloys, no treatment was performed. |
| O | Annealed |
| H | Strain-hardened or cold-worked |
| W | Solution heat-treated |
| T | Thermally treated |
For strain-hardened alloys, the first and second digits indicate the operation after straining hardening and the degree of strain hardening, respectively.
For thermally-treated alloys, the first digit indicates the thermal treatment condition.
Aluminum 1100 is used in fin stocks, heat exchangers, and heat sinks due to their high thermal conductivity. They are used in rivets, deep-drawn parts (e.g., pots, kitchen sinks), railroad tank cars, and reflectors. This grade is suitable for electrical applications.
Aluminum 2011 is used in the production of machine and automotive parts, weapons, munitions, fasteners, pipe and tube fittings, and atomizer parts. It is used to make screw machine products.
Aluminum 2024 is the best aluminum grade for aircraft and aerospace applications. It is also widely used in marine equipment, wing tension members, bolts, nuts, hydraulic valve parts, gears, shafts, couplings, and pistons.
Aluminum 3003 is used in heat exchangers, pressure vessels, storage tanks, and fuel tanks. It can be used in food handling instruments such as cooking utensils, pans, pots, ice cube traps, and refrigerator panels. It is also manufactured into building products such as roofs, sidings, gutters, garage doors, insulation panels, and downspouts.
Aluminum 5005 is used as a construction material in roofing, sidings, and furniture and as an electric conductor. It is also used in chemical and food handling equipment, HVAC equipment, tanks, vessels, and high-strength foils. Due to its bright appearance, it is helpful in decorative applications.
Aluminum 5083 is used in shipbuilding, vehicles, rail cars, pressure vessels, and drilling rigs.
Aluminum 5052 is used in food processing equipment, cooking utensils, heat exchangers, and chemical storage tanks. This grade is used in automobile and truck panels and components, flooring panels, rivets, wires, treadplates, and containers.
Aluminum 6061 can be made into tubes, beams, and angles with rounded corners. They are used in pipelines, tank fittings, railroad cars, trucks, marine components, and furniture.
Aluminum 6063 is widely used in architectural applications such as stair rails, furniture, window frames, doors, and sign frames. They can also be made into tubes, beams, angles, and channels.
Aluminum 6262 is used in screw machine products, hinge pins, knobs, nuts, couplings, valves, marine fittings, pipeline fittings, and decorative hardware.
Aluminum 7075 is preferable in aerospace and aircraft applications due to its high strength. It is also used in bike parts, competitive sporting equipment, molds, and industrial tooling.
The 1XX.X series are manufactured into electrical rotors.
The 2XX.X series are used in making automotive and aircraft engine cylinder heads, diesel engine pistons, bearings, and exhaust system parts.
The 3XX.X series are used in compressor and pump parts, automotive cylinder blocks and heads, motor parts, and marine and aircraft castings.
The 4XX.X series are used in pump casings, pots, pans, and dental equipment.
The 5XX.X series are used for decorative architectural applications and sand casting parts.
The 7XX.X series are used in automotive parts and mining equipment.
The 8XX.X series are used in slide bearings and bushings.
The following are the forms of aluminum products:
Aluminum foils are manufactured by flattening and reducing the thickness of aluminum sheets using a roll mill. The thickness of aluminum foils ranges from 0.2 mm to 6 microns. Aluminum foils are malleable, pliable, and can be easily bent and wrapped around objects. They are used as a packaging and electromagnetic shielding material and in other industrial applications.
Aluminum bars, tubes, and pipes are produced by an extrusion process, in which an aluminum billet is passed through the opening of a die by compressive force. The shape of the billet is transformed as it passes through the die. The extrusion process can produce a variety of parts with different cross-sectional shapes; this process can produce round, rectangular, square, and hexagonal bars, as well as hollow tubes and pipes. Moreover, it can be used to create parts with complex shapes, as long as the cross-sectional shape is constant.
Aluminum bars, tubes, and pipes are used as structural, aircraft, aerospace, automotive, marine transportation, and HVAC equipment components.
Aluminum sheets are produced by rolling aluminum slabs several times under high pressure until they are thinner and flatter. The thickness of aluminum sheets is under 0.249 inches.
Aluminum sheets are the most widely used form of aluminum products. They are used to manufacture cans, packaging materials, truck and automotive parts, cookware, and construction parts such as roofing, siding, and gutters.
Aluminum plates are manufactured like aluminum sheets, except that their thickness is above 0.250 inches. Hence, they are more often used in heavy-duty applications. Aluminum plates are used in transportation, aerospace, aircraft, marine, and military industries. They are also used to manufacture storage tanks and fuel tanks.
Aluminum wires are produced by pulling aluminum ingots through a die which reduces the diameter of the ingot while increasing its length. Due to their good electrical conductivity and high strength-to-weight ratio, they are used as an alternative to copper in electrical applications. However, aluminum wires used in this application are oxidized easily, thus resulting in the deterioration of the electrical wiring and potential fire hazard.
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