Aluminum Heat Treatment: the Ultimate Guide

Aluminum heat treatment improved mechanical and physical properties of aluminum. This guide takes you through the vital aspects of heat treating aluminum. Whether you wish to learn about annealing, quenching, natural aging or any other form of heat treatment – you will find all information right here.

What Is Aluminum Heat Treatment?

This refers to a method of enhancing the strength and toughness of a particular aluminum alloy subcategory to attain the required level. It is a process, which makes aluminum hardy and durably, thus suitable for different applications where such aspects are vital considerations.

Types Of Aluminum Alloys Suitable For Heat Treatment

2XXX Series Alloys; ordinarily, they contain copper additions ranging from 0.7 to 6.8% and exhibit high performance and strength but are relatively lightweight.

6XXX Series Alloys; they have an ultimate tensile strength of 18 to 58 ksi and are typically aluminum/magnesium silicon alloys. Aluminum alloys under this category are highly machinable and often used in welding fabrication industry.

7XXX Series Alloys; these alloys are wrought aluminum based on aluminum-zinc-magnesium-copper system.

8XXX Series Alloys; this series uses additions of silicon, magnesium, zinc, copper, iron, and boron.

Mostly, they exhibit high conductivity and excellent strength.

Types Of Aluminum Alloys Suitable For Heat Treatment
Aluminum Heat Treatment Standards

Aluminum Heat Treatment Standards

They include the following;

ISO 2107:2007(en): This standard establishes temper designations as required for identification of a wide range of product forms of aluminum alloys and wrought aluminum.

ASM2705E:ASM2705E,  or Aerospace Material Specifications standards, is quite common in aluminum heat treatments. Ideally, the ASM2705E standard certifies and audits heat treating equipment used specifically in automotive and aviation production and manufacturing.

This standard figures out elements like thermocouples and placement types utilized in system accuracy, calibration, and furnace temperature.

Advantages Of Heat Treating Aluminum

Advantages Of Heat Treating Aluminum
Advantages Of Heat Treating Aluminum

It offers several benefits in different applications, but the main ones are as follows;

Enhances Workability And Machinability

It improves manufacturability by eliminating internal stresses from the initial fabrication processes such as welding, stamping, and machining.

Increases Durability And Wear Resistance

The process typically hardens the surface material making it stronger, more durable, tougher, and more resistant to wear.

Improves Strength And Toughness

Heat treatment comes in handy in increasing the overall strength of aluminum material.

In essence, it makes the material suitable for various applications that require strength and toughness.

Enhances Magnetic Properties

Different aluminum variants tend to gain more magnetic properties when heat-treated.

A specific heat treatment method reduces the magnetic permeability, which is specifically vital if the part is used in electronic surroundings.

Makes Lightweight And Low-Density Material

Ideally, the process involves altering several mechanical properties of aluminum, making it more lightweight.

Creates Good Surface Finish

Aluminum heat treatment ensures you attain an ideal surface finish, which is fundamental in improving the overall application aesthetics.

Enhances Corrosion Resistance

It creates a layer on the surface material, which is significant in resisting corrosion substances.

Increases Design Flexibility

When you heat treat aluminum material, it increases its ability to design it into different shapes and sizes easily.

Improves Overall End Product Quality

Aluminum heat treating infuses different mechanical properties into the material.

Ultimately, all these beneficial properties tend to reflect in the final product, thus enhancing the quality to desired levels.

Annealing Aluminum Alloys Process

Annealing Aluminum Alloys Process
Annealing Aluminum Alloys Process

Often, a wide range aluminum alloys are exposed to work hardening, commonly referred to as strain hardening. It takes place when plastic deformation shapes aluminum alloy.

Plastic deformation triggers grain arrangements within aluminum material to slide beside each other along the sections known as slip planes. The more the process of plastic deformation continues, the fewer the slip planes remaining, which tend to be easy to deform. Therefore, additional pressure is needed to attain more deformation.

Once an aluminum alloy part attains this state, it is recognized to be work-hardened.  It is recommended to remove strain hardening from part as an ideal way of continuing deforming the material plastically.

Annealing aluminum alloys is essential since it helps in resetting crystalline grain structure and slip planes’ restoration. This enables continuous part shaping without the need for excessive force.

Aluminum alloy must be heated to around 570-770° F for a predetermined time to anneal it accordingly. The annealing time would range from 30 minutes to up to three hours, depending on various factors.

Primarily, time and temperature depend on two major aspects; part size being annealed and its alloy composition. Besides, annealing relieves possible internal stresses likely to change in part during different methods such as casting or cold-forging.

This stabilizes the aluminum alloy part and resolves concerns arising from internal strains like warping. Additionally, you can successfully perform annealing on aluminum alloys successfully considered as non-heat treatable. Annealing aluminum is best suited for cast, forged, or extruded parts.

Homogenizing Aluminum Alloys Process

Homogenizing Aluminum Alloys Process
Homogenizing Aluminum Alloys Process

Homogenizing aluminum refers to redistributing precipitating elements more uniformly throughout the metal material. The process entails heating the aluminum alloy part to a temperature close to its melting point, between 480 and 540°C.

Afterward, it is closely cooled and this trigger precipitating elements to become more uniformly redistributed all over the material. As such, it leads to a more workable part with a more even internal structure.

The process yields a skin of aluminum crystals or grains on the surface material. While the part cools inwards, it leads to a reasonably pure aluminum near the skin and a few areas close to the middle.

Hence, the elements of alloying precipitate out, locking aluminum grains intact. Cast parts result in a few areas within the material softening and others relatively sturdy.

It is possible to reduce segregation between regions and the resultant part regarded more workable for effective for forming by homogenizing. Typically, homogenizing aluminum part occurs by raising its temperature merely below its melting point.

Once the entire part attains the homogenizing temperature, it starts cooling gradually. It thus results in cast part with unbroken internal structure. Homogenizing aluminum alloy is beneficial in many ways, such as facilitating further working or eliminating imperfections.

It also creates a more workable material since it is flexible and easier to work with to make it an ideal material for producing the desired product. The other benefit of this process is it redistributes the alloying elements uniformly throughout the part.

In essence, this makes the part’s strength highly consistent, which is important in attaining desired results in different applications. And more importantly, homogenizing aluminum heat treatment facilitates auxiliary heat treatment processes like solution heat treatment.

Solution Heat Treatment For Aluminum

Solution Heat Treatment For Aluminum
Solution Heat Treatment For Aluminum

This process aims at attaining aluminum parts that are easy to work with but achieves it by adding a quenching step. It works by dissolving the different elements within the part, which are responsible for age-hardening process.

After these elements dissolve, they diffuse throughout the part until the internal structure becomes homogenous. This diffusion of elements thus leads to temporary material softness to make it easy to be worked.

The ultimate result of the attained softness is then locked in for a reasonable duration upon the part’s rapid cooling. As the aluminum part returns to the ambient temperature, dissolved elements begin to clump together, allowing the part to age-harden once more.

Primarily, the precise temperature for this process is dependent on aluminum alloy composition. However, it typically takes place within a range of 440°C to 527°C, but the ideal temperature should be within 154°C of objective temperature.

Failure to attain this temperature, solution heat treatment becomes unsuccessful. And if the temperature is relatively low aluminum alloy part is likely to lose its strength. On the other hand, too high a temperature leads to discoloration of the part, and critical elements are likely to melt.

Moreover, excessively high temperatures could lead to enhanced strain within the part. After aluminum alloy part reaches the constricted window for the objective temperature, it needs soaking. Soaking duration may vary from merely 10 minutes to up to 12 hours for relatively large and thick parts.

Quenching Of Aluminum Alloy

Quenching Of Aluminum Alloy
Quenching Of Aluminum Alloy

This process is carried out after solution heat treatment to allow postponing resumption of age-hardening process. In this case, the essence of quenching aluminum alloy is to freeze the trapped elements.

Also, you can use it for cooling aluminum parts fast enough that the alloying features fail to precipitate out as part cools. Ordinarily, the quench medium often varies based on different factors.

However, in many instances, the part can be submerged in cold or boiling water. In other cases, it can submerged in water-polymer solutions, forced air, or merely sprayed with water.

Nonetheless, water is regarded as the most effective quenchant for aluminum alloys. Even so, such parts can be stored at relatively low temperatures to extend the duration of softening from solution heat treatment lasts.

Quenching alone allows the softened state to last for a few hours. Thus, it is essential to ensure any form of quenching in solution heat treatment is done immediately after completing quenching. Or else, natural ageing begins, and the part is likely to become more complex to work with.

Other Techniques Of Aluminum Heat Treatment

Natural Aging Aluminum Alloy
Natural Aging Aluminum Alloy

This technique happens once aluminum alloy has undergone solution heat treatment. Ordinarily, the dissolved elements begin to precipitate out over time. As such, it makes the grains start locking into position, and this, in turn, enhances the natural strength of aluminum alloy, a process known as natural ageing.

Also known as age-hardening, it takes place at room temperature for about 4-5 days, with approximately 90% of total hardening taking place in the first day. Hence, it is advisable to shape aluminum parts faster after solution heat treatment.

Natural Aging Aluminum Alloy
Precipitation Hardening Aluminum Alloy

It is artificial hardening aimed at strengthening the aluminum alloy up to the optimum level. This is an important process since some alloys rarely attain maximum hardness when subjected to natural hardening.

Thus, precipitation ensures such aluminum alloys are heated to a specific temperature between 116°C and 238°C. However, the target temperature is usually within 35°F. The alloy then soaks for up to 24 hours, followed by cooling to room temperature. It leads to significant increase in the aluminum yield strength, marginally less of a decrease in ductility, and an increase in tensile strength.

Application Of Aluminum Heat Treatment

Automotive Industry
Automotive Industry

Several typical parts used in assembling motor vehicles such as engines, transmissions, suspensions, and exterior and interior trims are processed through this technique.

Aviation Industry
Aviation Industry

It comes in handy in making aircraft components, including turbines, engine cases, interior trims, etc.

Computer Industry
Computer Industry

Most parts of computer systems and related appliances are manufactured using heat-treated aluminum material to enhance their strength.

Heavy Machinery
Heavy Machinery

Different parts and components of various heavy machinery also incorporate heat-treated aluminum materials for strength, durability, and wear resistance.

Marine Industry
Marine Industry

Often, the marine environment is quite unforgiving hence the need for parts that can endure such conditions. Aluminum heat treating produces highly corrosion-resistance parts ideal for such environments.

Cooking Ware
Cooking Ware

Many aluminum cooking utensils are heat treated using various techniques to make them suitable for the task.

Manufacturing Lines
Manufacturing Lines

Various production lines use different machines integrated to offer a single functional unit. Most parts and components of such units are made with heat treated aluminum materials due to strength, corrosion resistance, and durability.

People Also Ask:

Can You Quench Harden Aluminum?

Yes.

You can always use water or light brine but the ideal quenching period for hardened aluminum often depends on actual part.

How Strong Is Heat Treated Aluminum?

It varies based on the actual alloying composition of the heat treated aluminum. However, the ultimate tensile strength often ranges from 103 to 276 Mpa with a total yield strength of about 20% elongation.

What Happens When Aluminum Is Heat Treated?

The dissolved elements start to precipitate out over time. As such, it triggers the grains to lock in place, and this ultimately proliferates the overall natural aluminum strength.

Is Aluminum Toxic When Heat Treated?

Not necessarily.

Heat treated aluminum is never toxic and does not exhibit any form of health effects on humans or the surrounding.

Will Heat Treatment Weaken Aluminum?

No.

Mostly, the alloying elements used in aluminum heat treatment enhance the strength of the final product. Thus, on the contrary, heat treatment strengthens aluminum.

Related Resources:

Work Hardening

Heat Treating Aluminum

Heat Treating Of Aluminum Alloys

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