Aluminum and aluminum alloys

Aluminum is found on the earth in its oxidized form known as Bauxite. Bauxite is further refined to produce Alumina (Aluminium Oxide – Al2O3). Approximately 40% – 60% Alumina i.e. Aluminium Oxide (Al2O3) can be extracted from Bauxite.

The Hall-Héroult electrolysis process (invented in 1886) further processes Alumina (Aluminum Oxide-Al2O3) to separate it from oxygen. This process made possible the production of Aluminium on a large scale and significantly reduced the production cost too.

Some of the very important properties of Aluminum which makes it a very lucrative metal are;

  • It is highly resistant to corrosion
  • It is non-toxic
  • Possesses good electrical and thermal conductivity
  • It is nonmagnetic.
  • Retains good ductility at sub-zero temperatures

Aluminum and aluminum alloys are very suitable for critical applications such as;

  • Space, aircraft and marine industries
  • Vessels and storage tanks
  • Automotive industries
  • Structural applications and many such consumer products.

[NOTE: ‘Aluminum’ and ‘Aluminium’ are essentially the same. The word ‘Aluminium’ is very popular in Non-American English.]

Melting point of Aluminium:

The melting point of pure Aluminum is 660°C (1220°F).  However, the melting point of the Aluminum alloys varies from  480°C to 660°C (900°F to 1220°F), depending on the alloying element.

Major alloying elements (with Aluminium):

Major alloying elements are copper, manganese, silicon, magnesium, and Zinc, etc.

Aluminum alloys are identified by a 4 digit number. The first digit represents the major alloying element, please see the table below;

aluminium designation identification

As explained above, the first digit represents the major alloying elements. However, the last three digits represent the following;

For 1XXX series (Pure Aluminum group)

  • The second digit indicates a consecutive modification of an original alloy
  • The last two digits indicate the minimum percentage of Aluminium

For alloys in 2XXX – 9XXX series (Aluminum with major alloying elements)

  • The second digit indicates a consecutive modification of an original alloy
  • The last two digits have no significance, it only shows that this particular series of metal belongs to the Aluminium alloy group.

1XXX Series:

  • This series is often regarded as the pure aluminum group. These alloys have the following characteristics;
  • The aluminum content shall be more than 99.0% in this group of alloys
  • Ultimate tensile strength for this group of alloys is between 69 MPa to 186 MPa (10 ksi to 27 ksi)
  • They have superior corrosion resistance and hence suitable for specialized chemical tanks and pipings
  • Good electrical conductivity hence suitable for bus bar applications
  • Comparatively poor mechanical properties hence not suitable for structural applications
  • These alloys are not heat treatable
  • They have very narrow melting range but are weldable
  • Can be welded with a matching filler metal (1XXX series) or with the filler alloys of 4XXX

Most common alloys in this group are the following;

  • 1060 (99.60% minimum aluminum) – Used in chemical process equipment, tanks, and piping.
  • 1100 (99.00% minimum aluminum) – Used in architectural and decorative applications, furniture, deep drawn parts, etc.
  • 1350 (99.50% minimum aluminum) – Used in electrical conductor wire, bus, and cable

2XXX Series:

Major Alloying element in this group of materials is copper along with aluminum, also called as Aluminium-Copper (Al-Cu) group.

  • The amount of copper varies from 0.7% to 6.8%. These alloys have the following characteristics;
  • Possesses high strength over a wide range of temperatures hence suitable for aerospace and aircraft applications
  • Some of the alloys in the 2XXX series are not considered weldable by arc welding processes because of their susceptibility to hot cracking and stress-corrosion cracking; however, other alloys in this series can be welded by arc processes.
  • These alloys are heat treatable
  • Can be welded with a matching filler metal (High strength filler of 2XXX series) or with the filler alloys of 4XXX series, which contain silicon (Si) or silicon and copper.

Most common alloys in this group are the following;

  • 2014 – Used in structures, structural and hydraulic fittings, hardware, and heavy-duty forgings for aircraft or automotive uses.
  • 2017 – Usage similar to 2014 and screw machine parts.
  • 2024 – Used in structural, aircraft sheet construction, truck wheel and used for cladding for good corrosion resistance
  • 2036 – Used in the automotive body sheet.
  • 2090 – Used in Structural work, high strength, and damage tolerant aerospace applications.
  • 2218 – Used in pistons, engine cylinders, forging alloy and parts which require good strength and hardness at a higher temperature.
  • 2219 – Used in structural work, aerospace tanks

3XXX Series:

Major Alloying element in this group of materials is manganese along with aluminum, also called as aluminium-manganese (Al-Mn) alloys group.

  • The amount of manganese ranges from 0.05% to 1.8%. These alloys have the following characteristics;
  • Ultimate tensile strength for this group of alloys is between 110 MPa to 283 MPa (16 ksi to 41 ksi).
  • These alloys are not heat treatable
  • Moderate strength, good corrosion resistance, excellent formability, suitable for use at elevated temperatures hence used for manufacturing of heat exchangers.
  • Due to moderate, not suitable for structural applications
  • Can be welded with filler alloys from the 1XXX, 4XXX, and 5XXX series, depending on their chemical compositions

Most common alloys in this group are the following;

  • 3003 – Used in Process and food handling equipment, chemical, and petroleum drums and tanks and general-purpose applications where slightly higher strength than 1100 is required.
  • 3004 – Used in sheet metal which requires higher strength than 3003.

4XXX Series:

Major Alloying element in this group of materials is silicon along with aluminum, also called as aluminum-silicon (Al-Si) alloys group.

The amount of silicon varies from 0.6% to 21.5%. These alloys have the following characteristics;

  • Ultimate tensile strength for this group of alloys is between 172 MPa to 379 MPa (25 ksi to 55 ksi)
  • This series of alloys are mainly used as filler metals for both fusion welding and brazing

5XXX Series:

Major Alloying element in this group of materials is magnesium along with aluminum, also called as aluminum-magnesium (Al-Mg) alloys group.

  • The amount of magnesium varies from 0.2% to 6.2%. These alloys have the following characteristics.
  • Ultimate tensile strength for this group of alloys is between 124 MPa to 352 MPa (18 ksi to 51 ksi)
  • They have the highest strength among the not heat treatable alloys
  • This series of alloys have good weldability
  • These alloys are used in a wide variety of structural applications, such as components of ships, vehicles, bridges and pressure vessels, etc.

Most common alloys in this group are the following;

  • 5005 – Used in the electrical conductor and architectural applications
  • 5050 – Similar to 3003 and 5005 but stronger. Good finishing qualities
  • 5052, 5652 – Used in Sheet metal applications which require higher strength than 5050. Good corrosion resistance, Storage tanks, boats, appliances.
  • 5083 – Used in cryogenics structures, unfired pressure vessels, marine components, tanks, railroad cars, drilling rigs.
  • 5086 – Used in marine components, tanks, tankers, truck frames.
  • 5154, 5254 – Used in unfired pressure vessels and tankers
  • 5454 – Used in structural applications and tanks for sustained high-temperature service
  • 5456 – Used in structures, tanks, unfired pressure vessels, marine components

6XXX Series:

Major Alloying element in this group of materials is magnesium and silicone along with aluminum, also called as Aluminium-Magnesium-silicon (Al-Mg-Si) alloys group.

  • The amount of magnesium and silicone is around 1.0%. These alloys have the following characteristics.
  • These alloys are heat treatable
  • Ultimate tensile strength for this group of alloys is between 124 MPa to 400 MPa (18 ksi to 58 ksi).
  • These alloys can be welded with filler metals from the 4XXX and 5XXX series

Most common alloys in this group are the following;

  • 6009 – Used in the automotive body sheet
  • 6010 – Used in the automotive body sheet
  • 6013 – Used in general structural applications, it has improved strength over 6061
  • 6061 – Used in structural work, architectural, automobile, railway, and marine applications, pipe, and pipe fittings. This alloy possesses good strength, corrosion resistance, good formability, and good weldability
  • 6063 – Used in Pipe, railings, hardware, and architectural applications
  • 6070 – Used in structural applications and piping
  • 6101 – Used for electrical conductors
  • 6262 – Used for Screw machine products and fittings
  • 6351 – Usage similar to 6061
  • 6951 – Used in brazing sheet core alloy

7XXX Series:

Major Alloying element in this group of materials is zinc along with aluminum, also known as Aluminum-zinc (Al-Zn) alloys group.

The amount of zinc varies from 0.8% to 12.0%. These alloys have the following characteristics;

  • These alloys are among the highest-strength aluminum alloys and very suitable for high-performance applications, such as aircraft and aerospace components.
  • The common base metals in this series are 7003 and 7005 and can be welded with the 5XXX series filler metal.

Most common alloys in this group are the following;

  • 7004 – Used in truck trailer and railcar extruded shapes
  • 7005 – Used in truck trailer and railcar extruded shapes
  • 7039 – used in Armor plate
  • 7075 – used in High-strength aircraft and other applications; cladding gives good corrosion resistance
  • 7079 – used in massive parts for aircraft and allied construction
  • 7178 – Used for Aircraft construction, strength slightly higher

Sandeep Anand

I am a Mechanical Engineer with more than ten years of work experience in the field of welding and NDT.

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