Various Aluminum Alloys for Manufacturing
Aluminum is one of the most versatile and widely used metals in manufacturing and production today. Its unique properties of being lightweight, highly conductive, durable, corrosion resistant, and easily machined make aluminum suitable for a vast range of applications across many industries. However, not all aluminum alloys exhibit the same characteristics and properties. There are numerous different aluminum alloys available, each with its own advantages, disadvantages, and ideal uses. In this comprehensive guide, we will examine the most common aluminum alloys used in manufacturing and discuss their compositions, properties, applications, and production methods.
Alloy Classifications
Aluminum alloys are broadly classified into two categories – wrought and cast alloys. Wrought alloys are produced by mechanical working methods like rolling, extrusion, and forging. They exhibit directional properties and are stronger than cast alloys due to the alignment of grains and working. Cast alloys are produced by casting methods like permanent mold, sand, and die casting. They are isotropic but weaker than wrought alloys.
Within wrought and cast alloys, there are thousands of specific alloy compositions categorized by a four-digit numbering system issued by the Aluminum Association. The first digit in the 1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx, 7xxx, and 8xxx series indicates the major alloying elements present.
1xxx – Minimum 99% pure aluminum (1xxx series)
2xxx – Copper (2xxx series)
3xxx – Manganese (3xxx series)
4xxx – Silicon (4xxx series)
5xxx – Magnesium (5xxx series)
6xxx – Magnesium and Silicon (6xxx series)
7xxx – Zinc (7xxx series)
8xxx – Other elements like lithium, iron, nickel, etc. (8xxx series)
Let’s take a closer look at some of the most commonly used aluminum alloys from the 1xxx, 2xxx, 5xxx, 6xxx, and 7xxx series.
1xxx Series Alloys
The 1xxx series alloys consist of 99% or higher aluminum content with only tiny amounts of other alloying elements. They exhibit excellent corrosion resistance, electrical and thermal conductivity, reflectivity, and workability. However, their strength is low compared to other alloy series. Some common 1xxx alloys include:
1100 – Commercially pure aluminum (99% min Al), excellent corrosion resistance and conductivity. Used for chemical equipment, electrical applications, and jewelry. Easy to machine and ductile.
1350 – Alloyed with 1% manganese, higher strength than 1100 while maintaining conductivity. Used for electrical applications and welding wire.
1200 – Alloyed with 99% Al and 0.05% silicon to prevent aluminum crystallization during casting. Used for chemical and food industry applications.
They are popular in electrical applications and foil products due to their high purity and conductivity. Limitations include low strength, hardness, and susceptibility to work hardening during machining.
2xxx Series Alloys
2xxx alloys are alloyed with copper, plus other elements like magnesium and silicon. Copper improves strength and machinability significantly while maintaining good corrosion resistance. Common 2xxx alloys are:
2024 – Alloyed with 4.4% copper, 1.5% magnesium, 0.6% manganese. Highest strength of 2xxx alloys, used for aircraft structures. Prone to corrosion.
2014 – Alloyed with 4.4% copper, 0.8% silicon, 0.8% magnesium. Lower strength than 2024 but has better machinability and corrosion resistance. Used for hardware and fasteners.
2219 – Alloyed with 6% copper, 0.3% manganese, and trace amounts of iron and silicon. Excellent weldability and higher strength than in 2014 and 2024. Used for fuel tanks, and structures.
2xxx alloys offer a good balance of medium to high strength, good formability and machinability, and reasonable corrosion resistance. Limitations are susceptibility to stress corrosion cracking. Used extensively in the aerospace industry.
5xxx Series Alloys
5xxx alloys contain magnesium as the major alloying element, which significantly improves their strength through solid solution strengthening while retaining good corrosion resistance compared to 2xxx alloys. Common 5xxx alloys include:
5005 – Alloyed with 0.8% magnesium. Moderate-strength alloy used for chemical tanks and marine hardware. Low cost, good welding, and finishing qualities.
5052 – Alloyed with 2.5% magnesium. Highest strength 5xxx alloy, used for marine and aircraft sheet metal, fuel tanks, and rivets. Good corrosion resistance and formability.
5454 – Alloyed with 3.1% magnesium. Excellent resistance to corrosion including marine atmospheres. Used for boat hulls, gangplank, and masts.
5xxx alloys offer excellent corrosion resistance, moderate strength, weldability and formability, and an attractive finish. Limitations are susceptibility to stress corrosion cracking and low elevated temperature strength. Used for marine components, storage tanks, and sheet metal work.
6xxx Series Alloys
6xxx alloys contain both magnesium and silicon, which together produce substantial precipitation hardening and strength improvements. They offer a good balance of medium to high strength coupled with excellent corrosion resistance. Common 6xxx alloys are:
6061 – Alloyed with 1% magnesium and 0.6% silicon. The most popular 6xxx alloy, provides good strength, machinability, weldability, and corrosion resistance at moderate cost. Used for structural applications, marine frames, pipelines, aerospace, and automotive components.
6063 – Alloyed with 0.7% magnesium and 0.4% silicon. Used for architectural extrusions, hardware, and ornamental parts. Good extrudability, high corrosion resistance, and excellent finishing. Low strength compared to 6061.
6005A – Alloyed with 0.6% magnesium and 0.6% silicon. Similar properties as 6061 but better extrudability and improved finishing. Used for architectural applications and custom extrusions.
6xxx alloys exhibit an excellent combination of good workability, machinability, strength, and corrosion resistance. They are one of the most versatile and widely used aluminum alloy series today. Limitations include moderate loss of strength when heated.
7xxx Series Alloys
7xxx alloys contain zinc as the primary alloying element, plus smaller amounts of magnesium and copper in some alloys. Zinc significantly increases strength through precipitation hardening. These are the highest-strength aluminum alloys but also the toughest to weld and machine. Some common 7xxx alloys are:
7075 – Alloyed with 5.6% zinc, 2.5% magnesium, 1.6% copper, and 0.23% chromium. Highest strength of all aluminum alloys, used for highly stressed aircraft components. Susceptible to stress corrosion cracking.
7050 – Alloyed with 6.2% zinc, 2.3% magnesium, 2.3% copper, and 0.12% zirconium. Slightly lower strength than 7075 but better stress corrosion resistance. Used for aircraft structural parts.
7475 – Alloyed with 5.7% zinc, 2% magnesium, 1.9% copper, and 0.19% chromium. Similar strength to 7075 but better fracture toughness. Used for aircraft structures and components.
7xxx alloys provide the highest strength but are the most difficult to machine and weld. They are susceptible to stress corrosion cracking and have lower resistance to corrosion than 2xxx and 6xxx alloys. Extensively used when high strength is critical like aircraft structures.
Aluminum Alloy Production
Now that we have examined the major wrought aluminum alloy series and their applications, let’s discuss how they are commercially produced. There are two main steps – melting and refining the alloy compositions, and mechanical working by processes like rolling, extrusion, and forging to create the desired product forms.
Melting and Refining
Aluminum alloys are first melted to the desired composition specifications in gas- or oil-fired reverberatory furnaces. The liquid metal may undergo fluxing with chlorine or other agents to remove dissolved gases and dissolved iron, which can cause defects. Once the molten alloy is refined, it is transferred to a holding furnace until ready for casting or further alloy preparation.
Additional alloying elements like magnesium, copper, and zinc may be added to the holding furnace to achieve the target composition. The melt is degassed using argon or nitrogen to remove dissolved hydrogen, which can cause porosity in castings. Final alloy chemistry is checked using spectroscopy before pouring the metal into molds or transferring it to casting equipment.
Mechanical Working
For wrought alloys, the refined molten metal is cast into ingots, slabs, billets, rods, or other shapes. It is then mechanically worked by processes like rolling, forging, extrusion, and drawing to create the desired wrought product forms. Rolling produces sheet, plate, and foil products. Forging makes pre-shaped parts like fasteners and fittings. Extrusion creates lengthy sections like rods, bars, pipes, and hollow or shaped profiles. The wire is made by drawing the alloy through successively smaller dies to reduce diameter.
Mechanical working aligns the grains and imparts strength through cold working. Heat treating and aging may be done after working to further enhance properties like strength. The finished product is checked against specifications and packaged for shipment to manufacturers and end users.
Summary
In summary, aluminum is infinitely recyclable and among the most sustainable of modern metals. There are numerous wrought and cast aluminum alloy compositions to match the needs of nearly any manufacturing or production application. The major alloy series – 1xxx, 2xxx, 3xxx, 5xxx, 6xxx, and 7xxx offer their own combinations of properties like strength, corrosion resistance, machinability, weldability, and conductivity. Aluminum alloys can be tailored through alloying additions and thermo-mechanical processing to achieve desired attributes. They are produced through melting, alloying, casting, and mechanical working steps to create versatile wrought and cast product forms. Aluminum alloys play a vital role in modern manufacturing across transportation, construction, packaging, industrial machinery, consumer products, electrical systems, and more.