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What Are Aluminum Extrusions?

What Are Aluminum Extrusions

Aluminum extrusions are elongated aluminum products created by the method of aluminum extrusion. But what is aluminum extrusion then? Aluminum extrusion is the process of forming shapes by pressing heated aluminum alloy through a die. This process hardens the metal and makes it much more durable.

What Is Aluminum Extrusion Process?

The aluminum extrusion process begins with a basic cylindrical form called a billet or ingot. During extrusion, aluminum in the form of billets is heated in an oven until becoming malleable enough to be formed. The temperature of billets must usually be at the vicinity of 500°C (930°F), it varies based on the alloy and is crucial for the final result. A hot aluminum billet is then placed on the hydraulic press where it gets subjected to the enormous pressure of 1,500 to 15,000 tons. The press squeezes the billet through a special orifice, called a die. Dies determine the final shape of a profile. After a profile is extruded, it gets cooled down, straightened, hardened, cut to size, and possibly subjected to a post-processing treatment.

What Is Needed to Make Aluminum Extrusions?

Aluminum: Aluminum is extracted from bauxite. Once mined, aluminum within the bauxite ore is chemically extracted into alumina through the Bayer process. In the second phase, aluminum is obtained by electrolysis. To improve the properties of the material, alloys are used, normally of the 6000 series (i.e. aluminum-magnesium-silicon) which are heat treatable.

Hydraulic press: An extrusion press provides over 1,500 tons of pressure, it is made up of a container, a die holder, and a piston.

Die or matrix: The components of a die are made of steel resistant to high temperatures. The openings are made by electrical discharge machining. For cleaning, they are subjected to nitriding, which also gives them surface hardness.

Pressure: Pressure is a factor that depends on multiple variables; raw material, the shape, the press itself and the temperature, and the diameter of a billet, and the surface of a die.

Aging oven: To get desired physical properties a process known as age hardening is performed. A temperature in such an oven is typically between 121°C (250°F) and 204°C (400°F).

What Alloys Are Used For Aluminum Extrusions?

The ease or difficulty of extruding a profile, which ultimately determines its price, is shown in this table:

Alloy

Extrudability index

EN AW 1080

160%

EN AW 1050

135%

EN AW 1200

135%

EN AW 3003

120%

EN AW 6060/6063

100%

EN AW 6082

60%

IN AW 2011

35%

EN AW 5086

25%

IN AW 2014

20%

EN AW 5083

20%

EN AW 2024

15%

EN AW 7075

10%

EN AW 6060 and 6063 alloys have the best extrudability index. This means they are the best choice for making profiles with complex sections.

Alloys with a high extrudability index can cause deformation of the profiles during handling, in addition to the impossibility of maintaining their shape, because they are very soft and cannot be heat treated.

Alloys with low extrudability do not flow well through a die, which does not allow profiles with complex sections to be made. In addition to their low productivity, this type of alloy requires heat treatment with very strict control, which also means a higher price.

What Are Aluminum Extrusions Used for?

Products manufactured by extruding aluminum represent more than 50% of the European market of aluminum products. Aluminum can be extruded in various geometries. Aluminum lends itself well to any aesthetic requirement. In addition to a wide choice of colors, various finishes can recreate different effects such as glossy, matte, or ones that recreate a surface very similar to that of wood.

Today, aluminum extrusions are widely used in architectural elements and structures such as doors, windows, partitions, fences, translucent façades, etc.

Furthermore, aluminum has a high electrical, thermal, and sound conductivity. This makes aluminum extrusions the ideal material for the construction of radiators, heat-conditioning equipment, food containers, and some musical instruments.

Custom aluminum extrusions with complex cross-sections are used to meet high precision requirements in the fields of electrical equipment, industrial machinery, or the automobile industry.

What Are Extrusion Dies?

Dies used for the extrusion of aluminum are disks made of heat-treated steel able to withstand great pressure and high temperatures. A die is placed at the end of a press. The shape of the die opening defines the shape of the cross-section of the final product required by the customer. From time to time dies have to be cleaned. In order to do that they are put in a vessel and are rinsed with a solution of heated NaOH.

Types of Extrusion Dies

Generally, the three types of dies are solid, hollow, and semi-hollow.

Solid Dies

Solid dies are utilized to extrude aluminum shapes without any hollows. The most common examples of these shapes are aluminum angles, trims, and beams. Such shapes are often a cheaper option.

Hollow Dies

Hollow dies create extrusions with sections fully circumscribed by metal. An example of this would be a hollow tube.

Semi-Hollow Dies

Shapes with voids partially circumscribed by metal are manufactured with semi-hollow dies. These shapes have more than one void. Due to a more complex design, the costs of making this type are higher.

Surface Finishes Applied for Aluminum Extrusions

Surface finishes must be applied to ensure the best quality of the final product. Surface treatments such as anodization and powder coating are the most common ones.

A whole aluminum profile gets immersed in electrolytic liquid, which brings forth an oxide layer that covers the material and gives it greater resistance to corrosion. The thickness of the layer that is formed and the processing time depend on the desired use of the product.

Anodized and powder-coated aluminum profiles are applied in multiple and diverse fields thanks to their advantages:

  • They are resistant to corrosion: once subjected to anodization, in fact, aluminum profiles enhance their natural characteristics becoming even more resistant and long-lasting;
  • Anodizing is often used as a necessary treatment for coloring: the anodized aluminum profiles welcome the paint more easily and make the color more stable;
  • They are long-lasting as exterior elements because they are very resistant to temperature fluctuations;
  • They are completely recyclable.

What Material Can Be Extruded?

Since the process of extrusion uses an iron die, the material must be softer than iron. Aluminum is the most commonly used material for extrusion.

The extrusion process can be applied to plastic, copper, bronze, brass, stainless steel, or titanium. Although it is the extrusion of aluminum that has become widespread due to its low melting point of about 500°C or 930°F.