This article is an investigation of the aluminum extrusion process and its basic elements.
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Extruded aluminum involves a process where a heated or cold aluminum billet is pushed through a die with a specified cross-sectional design. This technique creates aluminum components using an initial two-dimensional profile with defined width, height, and thickness. The profile's third dimension is established during the post-extrusion stage, which encompasses pulling the profile along a runout table and cutting it to the desired lengths.
Aluminum extrusion can occur through two methods: hot heading and cold heading. During hot heading, the billet is heated to roughly 25% below its melting point, whereas in cold heading, the billet is processed at ambient temperature. Each extrusion method has its advantages; hot heading is generally faster, while cold heading results in more durable products.
The extrusion of aluminum has gained recognition for its cost-efficiency in manufacturing, allowing for the production of parts with remarkable precision, tight tolerances, and consistent accuracy. Every extruded piece exhibits unwavering dimensions from the starting piece to the final cut, ensuring uniformity in all aspects.
Aluminum is highly valued for its lightweight properties, excellent strength, and corrosion resistance. In its natural state, it is relatively soft, but it gains enhanced mechanical characteristics when alloyed with elements such as copper, magnesium, manganese, and silicon. Moreover, aluminum may undergo heat treatments to reach its peak strength and workability.
The roots of metal extrusion can be traced back to the late 18th century, with Joseph Bramah, an English inventor, obtaining the first patent for the process. Initially used for creating lead pipes and cable sheaths, early extrusion methods were suitable for softer metals.
Extrusion of tougher, more robust metals like aluminum needed higher temperatures and pressures. It was not until Alexander Dick developed the hot extrusion process in 1894 that aluminum became feasible for extrusion purposes.
Aluminum extrusion is now widely utilized, with a global market value surpassing $67 billion. The market is expected to expand at an annual pace of 3.8% from 2020 to 2027. Extruded aluminum finds significant applications in sectors such as construction, automotive, transportation, consumer products, and electrical and energy industries.
Aluminum is the most widely used metal for extrusion forming due to its unique combination of mechanical properties, including high strength, low density, and excellent workability. Its favorable properties are maintained across a wide range of temperatures, making it an extremely versatile material for diverse industrial and engineering applications. Additional valuable characteristics such as high electrical conductivity, strong reflectance, environmental sustainability, and paramagnetic behavior further broaden the range of industries and product categories where aluminum alloys are preferred. These critical qualities explain why aluminum is integral to sectors such as aerospace manufacturing, automotive engineering, construction, electronics production, and consumer goods.
Below, we explore the core physical and chemical properties that make aluminum a go-to metal in modern manufacturing:
High Strength-to-Weight Ratio: Aluminum is widely popular due to its light weight—its density is about one-third that of steel—paired with high strength. Depending on the specific grade or alloy, aluminum can out-perform steel in strength by up to a factor of five. Due to this combination, aluminum is extensively used in aerospace components, automobile chassis and body panels, high-speed trains, and performance bicycles. This makes aluminum extrusions and profiles highly sought after for lightweight engineering.
Corrosion Resistance: Aluminum features inherently strong corrosion resistance compared to most other metals. This durability results from its natural tendency to form a thin, robust oxide layer on its surface, providing long-term protection against moisture and harsh environmental conditions. Because of this, aluminum extrusions and products are especially valued in outdoor structures, marine equipment, window frames, and building facades, where resistance to rust and corrosion is a key requirement. Surface coatings and anodization processes can further enhance these anti-corrosive properties.
Electrical Conductivity: With electrical conductivity at around 61% that of copper, aluminum wires and bars are often favored in power transmission, overhead cables, electrical busbars, and wiring applications due to both lower material weight and reduced cost. The high strength-to-weight ratio also means that aluminum conductors can span longer distances with less sag, improving efficiency in power grid systems and electronics manufacturing.
Thermal Conductivity: Aluminum is an excellent conductor of heat, ranking above brass and outperforming steel by up to four times. As a result, aluminum heat sinks, radiators, and thermal management components are essential in electronics, LED lighting, computer hardware, power electronics, and refrigeration systems, where rapid heat dissipation ensures high performance and reliability.
Ductility and Workability: Aluminum can be easily shaped, extruded, and formed at room temperature, making it ideal for manufacturing complex profiles and precision parts. In addition to extrusion, aluminum can be processed using methods like rolling, drawing, stamping, forging, and machining. This versatility is a critical benefit for fabricators, designers, and manufacturing engineers seeking flexible production solutions for custom applications or high-volume production runs.
Low-Temperature Toughness: Unlike steel and many other metals, aluminum retains its toughness and ductility even in sub-zero environments. Its resistance to brittle fracture under low-temperature conditions makes it an excellent choice for cryogenic applications such as liquid gas transportation, storage tanks, and aerospace systems operating at altitude or in extreme climates. The mechanical properties of aluminum remain remarkably constant across a broad temperature range, ensuring structural integrity in challenging environments.
Resilience and Impact Strength: Thanks to its natural toughness and resilience, aluminum has high impact resistance. Engineered aluminum parts can absorb forces from dynamic loads, vibrations, and shocks—making them suitable for crash protection systems, portable devices, heavy equipment frames, and safety barriers. Its ability to elastically flex and recover strengthens its reliability in demanding industrial settings.
Non-magnetic & Paramagnetic: Unlike ferromagnetic metals such as steel, aluminum is only paramagnetic, so it will not develop a magnetic charge when exposed to strong electromagnetic fields. This property is critical for electronic enclosures, shielding components, MRI equipment, electrical housings, and precision instruments where magnetic interference must be minimized. With its non-magnetic nature and electrical conductivity, aluminum is ideal for creating electromagnetic interference (EMI) shields in high-tech applications.
Reflectance: Aluminum exhibits the highest reflectance of any metal in the 200 to 400 nm ultraviolet range—outperforming gold and silver. Its superior optical properties make aluminum film or foil coatings a standard for producing mirrors, lighting fixtures, solar reflectors, and even advanced electronic displays. Depending on its surface finish and treatment, aluminum can reflect up to 90% of visible light, maximizing brightness and energy efficiency in architectural and industrial lighting design.
Recyclability & Environmental Sustainability: Aluminum stands out as one of the most environmentally responsible engineering materials. It is infinitely recyclable with no loss in its physical or chemical properties, making it central to sustainable manufacturing and green building initiatives. Recycling aluminum requires just 5% of the energy needed to refine new (virgin) aluminum, dramatically reducing the carbon footprint for manufacturers. As industries and governments prioritize eco-friendly materials and practices, recycled aluminum gains further importance in supply chains committed to sustainability.
Conclusion: Understanding the unique properties of aluminum—such as its high strength-to-weight ratio, corrosion resistance, exceptional conductivity, adaptability in fabrication, and environmental benefits—empowers engineers, designers, and manufacturers to make informed material choices for their projects. As demand for lightweight, energy-efficient, and eco-friendly materials grows, aluminum’s role will only continue to expand across industries. For those sourcing aluminum extrusions, custom profiles, or value-added aluminum fabrication services, a deeper knowledge of these fundamental properties ensures optimal product performance, cost-efficiency, and long-term sustainability.
The extrusion process, when combined with the properties of aluminum, offers distinct advantages that benefit both manufacturers and end-users. This process excels in producing parts with intricate cross-sections and can handle brittle materials that are challenging for other forming processes.
Ease of creating complex cross-sections. Complex parts can be made provided that it has the same cross-section throughout its length. The increment in operating cost for producing more complex parts is minimal compared to with other forming processes.
Seamless hollow parts can be formed: Hollow profiles can be made by extruding the aluminum through combinations of dies and mandrels. These profiles do not require mechanical joints or welded seams that are potential weak points for the product.
Good surface finish. Secondary operations can be integrated easily to create various kinds of finishes. The product's surface can be buffed or polished to achieve a mirror-like surface or brushed for a matte finish. Aside from polishing, aluminum extrusions can also be anodized, painted, powder-coated, electroplated, or laminated.
The standard finish is mill finishing, where the product is deburred and cleaned and made ready for anodizing, powder coating, or other secondary surface finishing. Sandblasting is a common surface treatment completed before anodizing. The types of anodizing finishes include clear and black, which are the most common anodizing finishes, with custom colors also available.
Anodizing is a finish that combines to the underlying aluminum with unmatched adhesion. The finishes are chemically stable, non-toxic; and heat-resistant. The thickness of anodizing is 6 ÎĽm to 18 ÎĽm and comes in black or clear, with customized colors available. The limitation of the anodizing process is the length of the extrusion since long extruded aluminum will not fit in the anodizing tank. Electrostatic spray coatings are also used to coat extruded aluminum and produce the highest quality products in a variety of colors.
Extrusion is classified as a bulk-forming process that involves a substantial change in the surface-to-volume ratio of the metal being formed. This process uses compressive forces applied to the billet using rams, punches, tools, and dies. The plastic theory is employed to ensure the production of the desired profile with a predictable grain structure, governing the mechanics of the metal's plastic deformation.
The characteristics of the formed product depend significantly on several variables, with extrusion pressure being a primary factor. This pressure is influenced by other parameters including temperature, extrusion ratio, and extrusion speed. The key extrusion variables are listed below:
Type of extrusion process: The two major categories are direct and indirect. Direct extrusion is a process where the ram travel and metal flow are in the same direction, while indirect extrusion is the opposite. Each process has its advantages and disadvantages. Other types of aluminum extrusion technologies have been developed such as hydrostatic and impact extrusion.
Die Type and Design: Dies are the components that deform the metal. Die design determines the mechanical working of the metal as it is being extruded. Extrusion dies can be solid, semi-hollow, or hollow dies.
The most widely used alloy for extrusion is the 6xxx series alloy.
Temperature: Aluminum extrusion is usually carried out in elevated temperatures, known as hot extrusion. High temperatures enhance metal flow producing extrudates without defects. However, the downside of using high temperatures is the increased rate of oxidation. Aluminum hot extrusion can range from 705 ° F to 932 ° F (375°C to 500°C).
Extrusion Ratio: This is defined as the ratio between the billet and the die opening cross-sectional areas. A larger extrusion ratio means larger deformation. This requires higher extrusion pressures. Moreover, higher deformation results in higher exit temperatures.
The manufacturing of aluminum extrusions begins with the production of aluminum billets, which are fed into the extrusion machine. Aluminum is refined from bauxite to produce alumina, or aluminum oxide. Oxygen is then separated from the aluminum through a reduction process to obtain pure aluminum. The virgin aluminum is smelted into ingots, which are used to create billets along with recycled aluminum.
Aluminum billets are supplied to manufacturing plants for creating end-use parts through various metal forming processes. In aluminum extrusion, the billet is typically heated to increase the metal's plasticity. The heated billet is then placed into a cylindrical chamber equipped with a ram on one end and a die on the other. The ram, powered either mechanically or hydraulically, applies sufficient compressive force to plastically deform the billet, forcing it to flow through the die. The setup may vary depending on the specific type of extrusion process employed.
Aluminum extrusions can be produced through different processes. These can be categorized according to the method of applying pressure to the billet, as summarized below.
As described by the graph, at the start of the extrusion, the required pressure starts to increase rapidly to its peak value known as the breakthrough pressure. Once the flow is initiated, the pressure decreases, and steady-state extrusion proceeds. When the loaded billet is almost consumed, the extrusion pressure reaches a minimum value, followed by a sharp rise as the remaining is compacted. The remaining billet that is not extruded is called the butt or discard, which is 5 to 15% of the billet.
Indirect Extrusion: In contrast with the direct extrusion process, instead of pressing the billet against the die, the die is pressed against the billet. A hollow ram is attached to the die, which compresses the aluminum billet, forcing it to flow. The direction of metal flow is opposite to the direction of ram travel. Regarding the generated frictional force, since there is no relative displacement between the billet and the chamber, there is no friction between the billet and the extruder chamber. The effect of the absence of this initial frictional force is described by the pressure-displacement curve shown in the image below.
As seen in the graph, the required pressure only rises to the steady-state extrusion pressure. Indirect extrusion proves to be a more energy-efficient process than direct extrusion. Despite this advantage, indirect extrusion fails to be a replacement for direct extrusion. This is because of the requirement to use a hollow ram which is weaker compared to a solid press. This limits the loads that can be applied to compress the billet. Hence, this process is only applicable for producing extrudates with small cross-sections.
Hydrostatic Extrusion: This process involves the use of a working fluid to force the billet through the die. In this process, the working fluid is compressed inside a sealed chamber that completely surrounds the billet, except at the tapered end, which is initially fitted to the die opening. The pressurization can be achieved by either pressing the fluid with a ram or plunger or by pumping more fluid inside the chamber. The former is known as constant-rate extrusion, while the latter is constant-pressure extrusion. Oil is typically used as the working fluid, with modified properties to resist degradation from high temperatures due to the heat from forming and compression.
Hydrostatic extrusion offers the best of both worlds from direct and indirect extrusion. This process solves the problem of the high frictional forces experienced in direct extrusion and the limitation on the cross-sectional area of the indirect process. However, they also suffer from disadvantages such as lower throughput due to the longer preparation per extrusion cycle and sealing difficulties at high pressures. Lower throughput is the consequence of the additional billet tapering process and the necessary injection and removal of fluid for every cycle. In some setups, instead of removing the fluid, the discard is retained to prevent the sudden release of the extrusion fluid. This discard is usually tougher due to cold working and will require additional compression to extrude. Sealing difficulties are from the tighter seal between the chamber and ram and the seal between the billet and die.
Cold Extrusion: In contrast with hot extrusion, cold extrusion is done below recrystallization temperatures, typically at room temperatures. The metal is initially at room temperature. As it is being compressed, heat is generated from the continuous deformation. The advantages of cold extrusion are superior hardness and strength, lower oxidation, better surface finish, and closer tolerances.
Enumerated below are the classifications of the extrusion process according to the direction of metal flow relative to the motion of the ram.
Lateral Extrusion: In a lateral extrusion process, the ram is oriented vertically while the extrudate flows horizontally. This is basically a modification of the forward extrusion process to save space or improve the pressurizing efficiency of the ram.
The aluminum extrusion process is inherently complex. Fortunately, there are numerous manufacturers of extruded aluminum equipment in the United States and Canada who have essentially perfected this process. Below, we highlight several of these manufacturers and their machines.
The SMS SmartExtruder is a technologically advanced extrusion machine manufactured by SMS Group. It is designed to enhance productivity and efficiency in aluminum extrusion. This model features intelligent control systems, energy-efficient operation, precise temperature control, and advanced automation capabilities. Known for its versatility, the SmartExtruder can handle a wide range of extrusion profiles while ensuring consistent quality.
The Presezzi Extrusion Press Series 7 is renowned for its advanced design and high precision in aluminum extrusion. It incorporates state-of-the-art automation, superior control over the extrusion process, and energy-efficient performance. This model offers versatility in handling various extrusion profiles and alloys, enabling reliable and high-quality production of extruded aluminum.
The UBE Aluminum Extrusion Press by UBE Machinery is celebrated for its advanced technology and superior performance in aluminum extrusion. It features precision control systems, efficient energy utilization, and high-speed capabilities. This model offers versatility in handling different aluminum alloys and extrusion profiles, ensuring precision and reliability throughout the extrusion process.
HPM (Hamilton Plastic Molding) manufactures the HPM Aluminum Extrusion Press, designed for high productivity and precision in aluminum extrusion. These presses feature advanced control systems, efficient energy consumption, and the capability to handle a wide range of extrusion profiles and alloys. HPM presses are known for their robust construction and reliability in industrial applications.
SMS Elotherm specializes in induction heating systems for aluminum extrusion processes. Their Induction Billet Heating Systems provide precise and efficient heating of aluminum billets. Incorporating advanced induction technology, these systems offer precise temperature control and energy-efficient operation. SMS Elotherm systems are designed to achieve uniform heating and optimal billet malleability, ensuring high-quality extrusions.
Please note that specific model availability may vary, and for the latest information on models and features, it's recommended to contact the manufacturers directly or consult their product catalogs.
In the design of aluminum products, choosing the right alloy is crucial for creating high-quality extruded aluminum. Alloy selection determines many aspects of the final product, especially its strength and durability. Heat treatment is applicable primarily to heat-treatable alloys, enhancing their mechanical properties.
Tempering is a process that involves mechanical, chemical, or thermal treatment of extruded aluminum. It can include softening or annealing, cold working, or spring tempering. There are five forms of tempering for aluminum, each of which is designated by the letters F, O, H, W, and T, with certain tempers having subdivisions. The various letters of the tempering designations refer to the potential physical properties that can be achieved.
Aluminum alloys in series 1xxx, 3xxx, and 5xxx are not heat treatable, while series 2xxx, 6xxx, and 7xxx are heat treatable. Series 4xxx comprises both heat treatable and non-heat-treatable alloys. The strength of non-heat-treatable alloys depends on their inherent properties and cold working. The chemical composition and metallurgical structure of alloy groups dictate their fabrication characteristics.
All aluminum products are distinguished by their properties, alloy, and temper designation. Understanding these aspects is crucial when selecting the appropriate aluminum alloy for producing an extruded aluminum profile. While various processes play a significant role in the selection process, the type of aluminum alloy and its temper designation are fundamental factors that must be carefully considered.
Alloy designations consist of four-digit numbers that denote the alloy's chemistry. The first digit indicates the primary alloying element, such as copper, manganese, silicon, or zinc. Pure aluminum, which starts the series, is denoted by the number 1. The second digit signifies modifications to one of the alloying elements. The last two digits, numbers 3 and 4, identify the specific alloy within the series, except for the 1xxx series where the last two digits indicate aluminum content between 99% and 100%.
| Aluminum Numbering System as Established by the Aluminum Association | |
|---|---|
| 1xxx | Pure Aluminum |
| 2xxx | Copper |
| 3xxx | Manganese |
| 4xxx | Silicon |
| 5xxx | Magnesium |
| 6xxx | Magnesium and Silicon |
| 7xxx | Zinc |
| 8xxx | Other |
Temper identifications are alphanumeric and are added with a dash after the alloy series number. The letter in the temper designation describes the mechanical and thermal treatments applied to the alloy. Each letter in the temper designation indicates a specific class of treatment.
The main purpose of tempering is to enable designers to achieve desired mechanical properties. The strength of an aluminum alloy can be significantly enhanced from a few thousand to several through the use of tempering. This increased strength is possible using a combination of solution heat treatment and artificial aging. Tempering can also change an alloy's characteristics and how it will react to different fabrication processes.
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