Heat treatment is the process of heating or chilling to an extreme temperature to achieve a desired shape through the hardening or softening of a material.
Heat treatment of aluminum and copper undergoes almost the same heat-treating process. But their results are different. The methods of annealing, homogenizing, and solution heat treatment on copper and aluminum give different results.
Since there are different applications made with aluminum, meeting the requirements of the items will require aluminum to undergo heat treatment. Heat treatment alters the properties of aluminum to achieve a desired characteristic. In this reading, we’ll explore how to heat treat aluminum and aluminum alloy, and their methods
Let’s begin!
Learn about Heat Treatment with this detailed guide!
Heat Treatment of Aluminum & Aluminum Alloys
Heat treatment of aluminum and copper undergoes almost the same heat-treating process. but their result is different. The processes of annealing, homogenizing, and solution heat treatment on copper and aluminum give different results.
As previously explained, copper undergoes annealing to soften hardened materials. It is done on aluminum to achieve strain-hardened material, unlike copper, which loses its hardening (strain hardening) when annealed.
The same occurs with homogenizing. Heat treatment of aluminum is carried out to increase the strength and hardness of a certain subset of aluminum alloys that are hardened by precipitation.
Heat treatment involves subjecting metal parts to specific temperatures for predetermined durations to modify their properties. This treatment can harden, soften, or relieve stress from the metal without altering its physical shape.
Aluminum tempering designations, like W, T4, or T6, indicate the desired level of treatment. One common treatment takes an O metal to a W temper, and after being heated for an hour, the part is dipped into a quench tank to cool. Further treatments can strengthen the metal, remove stress, or make it easier to form.
Methods of Aluminum Heat Treatment
Different requirements for aluminum properties lead to various heat-treating processes. Below are the heat treatments for aluminum and aluminum alloys: annealing, homogenizing, solution heat treatment, natural aging, and artificial aging.
Annealing
Aluminum alloys obtain strain hardening when subjected to work. It occurs when the material is plastically deformed, which causes the grain structure within the aluminum to slide against each other along the slip plane area.
The purpose of such aluminum alloys is to restore the crystalline grain structure and the slip plane. Helping the continuation of the shaping with low force. In other words, to relieve internal stresses that are developed during operation, such as cold forging or casting.
Annealing is achieved on aluminum alloys when the material is heated at about 570 to 770 degrees Fahrenheit, which takes about 30 minutes to 3 hours.
The composition of the alloys and the size of the material determine the temperature and time. The rate of cooling is not critical. That is, it has no effects after the annealing process is achieved.
Learn about Annealing with this detailed guide!
Homogenizing
Homogenizing is done to distribute the precipitation elements more evenly in an aluminum part. It is achieved by raising its temperature below its melting point, usually between 900 degrees Fahrenheit and 1000 degrees Fahrenheit.
If the homogenizing temperature reaches 100 °C, the aluminum is allowed to slowly cool.
Solution heat treatment
The purpose of solution heat treatment is to allow the metal part to easily work. The process involves heating the aluminum part at a specific temperature, which varies based on the alloy composition of the aluminum.
The temperature should specifically be within the range of 825 degrees Fahrenheit to 980 degrees Fahrenheit. If we cannot obtain the exact temperature, the operation will not be successful.
If the temperature is too low, strength is lost; if too high, the part may melt and discolor. Alternatively, the part may experience an increase in strain. When the part reaches the target temperature, it saturates.
This soaking time can range from 10 minutes for the materials to 12 hours for longer or thicker parts. At this point, the part undergoes quenching.
The quenching or rapid cooling, helps to preserve the final distribution of dissolved elements in the alloy that was achieved. that is, to “freeze” the trapped elements or cool the aluminum part fast enough to keep the alloying element from precipitating out. The part is commonly cooled with water.
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Natural aging
Aluminum that undergoes solution heat treatment will precipitate out after some time, which will cause the grain to lock into position, helping to increase the natural strength of the part.
The natural aging or age-hardening process takes place at room temperature within four to five days, obtaining at least 90 percent of the hardening within the first day. For this reason, aluminum materials are shaped rather quickly after they undergo solution heat treatment.
Artificial Aging (Precipitation Hardening)
Artificial hardening is done when an aluminum part needs maximum hardness, which is not achieved during natural aging at room temperature.
To achieve this, the dissolved elements need to be fully precipitated out, which is done by subjecting aluminum to heat in an alloy at a specific temperature. Typically, this process occurs at temperatures of 240 degrees Fahrenheit and 460 degrees Fahrenheit, respectively.
At this point, it is soaked for about six to twenty-four hours and then cooled to room temperature. the aluminum part will then increase in yield strength, show a slight increase in tensile strength, and decrease in ductility.
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Conclusion
Heat treating aluminum and its alloys is a precise process that enhances strength, corrosion resistance, and workability, making it ideal for aerospace, automotive, and structural applications. Unlike steel, aluminum requires controlled heating and aging cycles such as solution heat treatment, quenching, and artificial aging (precipitation hardening).
Not all aluminum alloys are heat-treatable, so it’s crucial to know the specific alloy series before starting. With proper heat treatment, aluminum can deliver a perfect balance of lightweight performance and durability tailored to specific engineering needs.
FAQs
Can all aluminum alloys be heat treated?
No. Only heat-treatable aluminum alloys, mainly from the 2xxx, 6xxx, and 7xxx series, can be strengthened through heat treatment. Non-heat-treatable series like 1xxx, 3xxx, and 5xxx are typically strengthened by cold working instead.
What is solution heat treatment?
It involves heating the aluminum alloy to a high temperature (typically 900–1000°F or 480–540°C) to dissolve alloying elements, followed by rapid quenching to retain those elements in solution.
Why is aluminum quenched after heat treatment?
Quenching “freezes” the alloying elements in place, creating a supersaturated solid solution. This sets the stage for further strengthening during the aging process.
What is aging or precipitation hardening?
Aging is a post-quench process where the aluminum is heated to a lower temperature (around 250–375°F or 120–190°C) to allow fine particles (precipitates) to form, which strengthens the metal.
What’s the difference between natural and artificial aging in aluminum?
Natural aging occurs at room temperature over time, while artificial aging uses controlled heating for faster and more consistent results.
How do I know the right heat treatment for my aluminum alloy?
Refer to the specific alloy designation and manufacturer’s datasheet, as each alloy has its own recommended temperatures and durations for solution treatment and aging.