How to Choose the Alloy and Temper of Aluminum Extrusion
Pure aluminum has limited usage for extrusion purposes due to its low strength and softness. As such, aluminum is alloyed with other elements to give it various mechanical properties suitable for different applications. The common alloying substances include iron, silicon, manganese, magnesium, zinc, and copper.
As an aluminum profile extruder, you must be competent in metallurgy to ensure you use the right alloy based on your production needs. Aside from alloy selection, the temper designation of the metal also influences the performance of aluminum extrusions. Temper refers to the strength or hardness that thermal or mechanical treatment gives the metal.
Manufacturers can further hone the physical properties of an aluminum alloy with an appropriate temper. These properties may include ductility and corrosion resistance. There are more than 600 aluminum alloys and a wide variety of tempers to consider. Below is a comprehensive guide on how to select the right alloy and temper for aluminum extrusion.
Types of Aluminum Alloys and Their Applications
An in-depth understanding of the types of aluminum alloys available helps manufacturers choose the most suitable for different applications. The alloys are categorized in grades, which are denoted with a 4-digit identifier. The first digit identifies the series of the alloy based on the primary alloying elements.
Note that aluminum alloys can be heat treatable or non-heat-treatable. Heat treatable alloys allow for precipitation hardening. Non-heat-treatable options depend on cold working and strain hardening for their strength properties.
1xxx Series - Pure Aluminum
This series of alloys represents commercially pure aluminum with a minimum of 99% aluminum content. 1xxx series alloys are strain harden able and have very high formability. They also have exceptional electrical conductivity and corrosion resistance.
Manufacturers can readily join products made from these alloys by soldering, brazing, and welding. 1xxx series alloys are not an ideal option if strength is a major consideration. The main uses of these aluminum alloys are applications where workability and high corrosion resistance are important.
They are great options for extrusions used in chemical equipment, automobile bodies, and food packaging. The alloys are also well suited for electrical applications. This is because certain alloys in the series, such as 1350, have minimal impurities that can affect electrical conductivity.
2xxx Series - Aluminum Copper Alloys
These alloys are heat treatable and have a beneficial combination of high strength, durability, and machinability. 2xxx series alloys have especially high strength at elevated temperatures.
This makes extruded products suitable for aeronautical and truck body applications, where high strength and toughness are crucial. Applications that utilize 2xxx series aluminum alloys include:
● External and internal aircraft structures
● Structural beams of trucks and trailers
● Booster rockets and fuel tanks in aerospace
● Structural members in railroad vehicles
3xxx Series - Aluminum Manganese Alloys
The main properties of this series of alloys are medium strength, high workability, and excellent corrosion resistance. They are non-heat-treatable and can be readily joined by the usual fabrication methods.
3xxx series alloys are primarily used in chemical equipment, builder’s hardware, and cooking utensils. Due to their formability, these alloys are also applied in heat exchangers in power plants and vehicles.
4xxx Series - Aluminum Silicon Alloys
These alloys are heat treatable and have great flow characteristics. They have medium strength and are readily joined by soldering and brazing.
The main applications of 4xxx series aluminum alloys come from its flow characteristics, provided by the silicon content. The alloys are ideal for forgings as well as structural and automotive body applications. However, manufacturers generally don’t use these alloys for extrusion purposes.
5xxx Series - Aluminum Magnesium Alloys
5xxx series alloys have low to moderate strength and are strain harden able. Other characteristics include exceptional corrosion resistance, durability, and weldability. The toughness of these alloys means extruded products are suitable for building and construction, of road structures like bridges, pressure vessels, storage tanks, and marine applications.
6xxx Series - Aluminum Silicon Magnesium Alloys
The 6xxx series aluminum alloys are by far the most popular option for extrusion. These moderate strength alloys are heat treatable and have excellent extrudability and corrosion resistance. The alloys enable manufacturers to produce complex architectural forms in single shapes. They also allow producers to design extrusions that bear high compressive and tensile stress.
These characteristics are crucial for structural and architectural members where stiffness is vital. Extruding 6xxx alloys places less stress on and reduces wear in extrusion dies and associated tooling. The alloys also provide excellent surface finishes and favor production economics due to their relatively low cost.
For many manufacturers, the first choice for extrusion processes is alloy 6063. It is easily extruded and therefore suitable for complex geometries, including hollow shapes. It’s the best choice for tubing, window and door frames, and heat sinks.
Higher strength alloys in the series such as 6061 are ideal for welded structural components. These include railroad cars, pipelines, marine and truck frames, and medical equipment.
7xxx Aluminum Zinc Alloys
7xxx series alloys are heat treatable and have very high strength. It has the highest strength of any aluminum alloy but poor corrosion resistance. These alloys are primarily used in the aircraft industry, where lightweight strength and fracture toughness are critical. For instance, various aircraft wing structures utilize stiffened 7xxx aluminum extrusions.
Considerations When Selecting Alloys for Aluminum Extrusion
Manufacturers consider several factors when choosing aluminum alloy to ensure extrusions can handle their application needs. Strength and weight requirements are especially crucial. When aluminum extrusions are used as structural components, manufacturers select alloys based on the stress they can withstand.
The strongest aluminum alloys are heat-treated 7xxx and 2xxx series alloys. Pure 1xxx series alloys have the lowest strength ratings. However, the most commonly used alloy for structural purposes is alloy 6061, which can be heat-treated to enhance its strength further. Also, aluminum alloys have different densities. This can determine the overall weight of extruded products.
Design factors include the complexity of the profile shape and the wall thickness of the extrusion. 6xxx series alloys are the best choice for products with thin walls and complex shapes. These alloys, particularly 6063 and 6360, have less distortion and produce uniform extrusion shapes.
Corrosion resistance is also important for aluminum extrusions. It encompasses chemical corrosion, environmental elements, and other aspects. 1, 3, 5, and 6xxx series alloys have good corrosion resistance. The 2xxx and 7xxx alloys have poor corrosion resistance. Manufacturers can apply various finishes and treatments like anodizing, powder coating, and painting to improve the corrosion resistance of aluminum extrusions.
Finishing requirements is also an important consideration. For many applications, the aesthetics of the final extruded products matter. Again, the 6xxx series alloys allow for a wide range of mechanical and chemical finishing that enhances the appearance of extrusions. These alloys produce a lustrous finish making them ideal for architectural and decorative applications.
Another key factor that manufacturers look at is follow-on machinability. This includes cutting performance, formability, and weldability, which facilitate the fabrication of a functional end product. Generally, non-heat-treatable alloys have superior machinability compared to their heat-treated counterparts.
Choosing the Right Aluminum Alloy Tempers
In addition to the type, the temper designation of an aluminum alloys affords it different properties and characteristics. Tempering refines the mechanical properties of aluminum alloy. This can influence performance aspects such as toughness, hardness, and yield strength.
It also determines how the alloy will react to fabrication processes including forming, punching, and welding. Aluminum alloys have alphanumeric temper designations, which indicate the methods of thermal or mechanical treatment used to achieve its specific properties. There are five general classes denoted by characters:
● T – Heat-treatable alloys that have been thermally treated, quenched, and aged.
● O – Annealing treatment is used to produce low strength tempers for better workability and ductility.
● H – Strain hardening tempers. These alloys have improved strength following work hardening. The products may undergo additional heat-treating.
● F – Fabricated or free machining temper. Semi-finished alloys that manufacturers thermally treat, finish, and shape to produce other tempers or finished products.
● W – Naturally aging alloys that have undergone solution heat treatment.
These aluminum alloy tempers have further classifications denoted by single, double, or triple digits after the respective characters. The digits indicate various aspects such as heat treatment methods, work hardening methods, and degree of hardening. Alloy tempers offer the metal additional strength, enabling aluminum to be a viable alternative to steel.
Overall, the choice of temper for extrusion projects depends on various factors. The most important include strength requirements, formability, and corrosion resistance. Heat-treated tempers (especially T6) are the strongest and stiffest tempers. This alloy temper is ideal for structural extrusions where strength and impact resistance are crucial. F temper alloys are relatively soft but have moderate strength and workability.
Tempers can improve or reduce the formability of extrusion alloy. Annealed (O) temper is the most ductile and softest temper. It’s therefore suitable for products where ductility is a priority over strength. Tempers such as T4 and T5 also have good formability, making them ideal for shaping during extrusion.
Tempering can also influence an alloy’s resistance to corrosion. Heat-treated tempers enhance corrosion resistance and are suitable for products used in challenging environments. Generally, extrusion manufacturers prefer heat-treated tempers since they provide the best blend of strength, workability, and corrosion resistance.
Conclusion
Selecting the right aluminum alloy and temper for extrusion plays a major role in the performance of the final product. This crucial aspect of the extrusion process helps mitigate potential design and functionality issues saving time and resources. A reputable manufacturer has extensive metallurgy knowledge to ensure their products deliver the required performance for specific applications.