Understanding Aluminum Alloys

July 14, 2015
aluminum alloys

Aluminum can be manufactured in more variety than almost any other metal in the industry. People in the architectural and industrial industries seem most interested in aluminum because of its inherent combination of being both lightweight and durable.

There are 7 different alloys commonly used in aluminum manufacturing. Each series starts with a number 1-7 (1xxx, 2xxx, 3xxx, 4xxx, 5xxx, 6xxx & 7xxx). That number basically determines what alloying element has been added to the aluminum.

A very brief description of the different series is listed below:

  • 1000 Series is the most pure of aluminum—required to have 99% minimum aluminum. It is weldable but under narrow guidelines. Because of its superior corrosion resistance, it is mainly used in specialized chemical tanks or conductive bus bars.
  • 2000 Series aluminum is mixed with copper alloys and is often used for aircraft and aerospace industries.
  • 3000 Series is mixed with manganese and is very “formable” and heat treatable. This aluminum alloy is often used for cookware and heat exchangers in power plants and vehicles.
  • 4000 Series mixes aluminum with silicon, allowing for a lower melting point which improves fluidity when molten (sort of a fancy way of saying it melts well). The 4000 Series aluminum is often used as filler material for welding and brazing.
  • 5000 Series aluminum is mixed with magnesium (different than manganese) and has both a high tensile strength and formability; hence it is widely used in fabrication such as transportation, tanks, vessels and bridges.
  • 6000 Series is mixed with magnesium and silicone and used predominately in the form of extrusions and structural components like angles, beams and tubes.
  • 7000 Series is mixed with zinc alloys. It comprises very high strength aluminum and is often used in high performance applications like aircraft, aerospace and competitive sporting equipment.

The most common aluminum used in the general fabrication industry is 3000, 5000 or 6000 series alloys.

building with aluminum metal work

It’s important for engineers and architects to have a strong understanding of different types of aluminum for aluminum welding and fabrication, and its many alloys when requesting a specific type for a project. For example, when it comes to the 6000 Series aluminum, engineers often request 6061-T6 aluminum. This type of aluminum alloy has a high tensile strength but is also quite brittle. So, it might meet the tensile requirements for a designed part, but fail when the part has to be formed or fabricated because the metal will fracture at the bend line.

Because of this fracturing issue, fabricated aluminum, like that used on wall panels, general industrial fabrication, etc., would be better engineered with 5000 Series aluminum, which forms very well (without cracking or fracturing) but also has a reliable tensile strength.

In many instances, extrusions like Aluminum angle, tubing or beams might be used in conjunction with flat sheet materials in which case the alloys will not be exactly the same. In these cases, fabricators need to make sure the welding filler materials are accurately selected to manage both alloys. For example, 6000 Series aluminum should not be welded with 3000 series filler materials.

There are other aluminum fabricating and manufacturing issues as well—laser cutting already tempered aluminum can be a factor, correct aluminum welding and fabrication procedures as mentioned above, paint and finish—all of these require special attention to manufacture aluminum well.

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