Aluminum 6061 is the most commonly used aluminum alloy in the world—and for good reason. In addition to its light weight, excellent corrosion resistance, and other desirable properties, it also tends to be highly workable, weldable, and machinable, making it great for all types of manufacturing processes.
However, not all 6061 aluminum is the same. The machining properties of 6061 aluminum depend on its temper or how it is heat-treated, and understanding the effects of these tempers is essential for anyone working with 6061.
In this post, we’ll look at the various tempers available and how they affect the machining properties of 6061 aluminum.
What Are Aluminum Tempers?
To understand the machining properties of 6061 aluminum, it’s important to understand the temper and how it affects the material. Tempering is a heat treatment applied to aluminum to increase its strength and hardness. It improves the workability and ductility of the material by relieving stresses that may have accumulated during the hardening process. Tempering helps create the desired characteristics, such as machinability and durability, that are required by the end application.
There are five main aluminum tempers, each designated by a letter and a description of the type of treatment the alloy received to achieve its desired properties:
- F: As Fabricated
- O: Annealed
- H: Strain-Hardened
- W: Solution Heat-Treated
- T: Thermally Treated
An aluminum alloy’s temper designation appears at the end of the alloy designation. For example, annealed 6061 aluminum is 6061-O. The T group includes several variations designated by additional characters—for example, 6061-T6. The H designation is used primarily for non-heat-treatable alloys and doesn’t apply to 6061, which is heat-treatable.
Now, let’s look at each temper in more detail to see how they are achieved and how they affect the welding, forming, and machining properties of 6061 aluminum.
6061-F: As Fabricated
6061-F is produced with no special control over the thermal conditions and typically no specified mechanical properties. Most 6061-F products are considered semi-finished and must be subsequently worked, finished, or processed to achieve other tempers.
Annealed aluminum has been heated to a temperature high enough to reset the grain structure of the material, which removes the effects of any prior working or thermal treatments. The material is then allowed to cool slowly and recrystallize. This removes dislocations and internal stresses, resulting in a low-strength, low-hardness condition.
6061-O is soft and ductile, making it great for forming and welding operations. However, its machining properties are poor. The soft material produces gummy chips that can cause galling, and the workpiece can be easily deformed by the heat generated by the cutting tool.
6061-W: Solution Heat-Treated
Solution heat-treated alloys are heated to a high temperature, held there for a certain amount of time, and then quenched rapidly. As with the F temper, the W temper usually doesn’t have specified properties and is treated as a semi-finished product.
After it’s quenched, the yield strength of 6061-W gradually increases over time until it is further treated to stabilize its properties. This natural aging process distinguishes it from the T temper, which can be given additional treatments after quenching.
6061-TX: Thermally Treated
The T temper applies to any heat-treatable alloy that has been solution heat-treated, quenched, and aged either naturally or in a furnace. This is the most commonly used type of temper for 6061 aluminum.
The T temper has many variants, each designated by a number representing the way it was heat-treated, cold worked, and aged. The first digit after the T indicates the basic type of treatment, and any additional digits indicate whether and how it was stress-relieved and whether it received any other special treatments.
The table below shows some of the more common aluminum 6061 T temper designations:
|Solution heat-treated and aged naturally to a stable condition||Good||Poor||Excellent|
|6061-T51||Extruded, cooled, and artificially aged||Poor||Fair||Excellent|
|Solution heat-treated and artificially aged||Poor||Good||Excellent|
6061-T6 is one of the most commonly requested tempers of aluminum 6061 for machining applications. To produce this temper, a 6061-O billet is heated to about 900˚F, quenched in water, and then artificially aged for several hours in a furnace. The artificial aging process permits precipitation hardening, which increases the surface hardness and makes the material less gummy and easier to machine.
Compared to other tempers, the machining properties of 6061-T6 aluminum make it much easier to cut. However, the properties that improve its machinability also reduce its formability, making it more difficult to shape.
Helping Our Customers Understand the Machining Properties of 6061 Aluminum
With all of the different tempers of 6061 aluminum, it can be a challenge to select the right one for a particular application. It’s important to understand the various tempers available so you can make an informed decision on your next raw material order.
At Industrial Metal Service, we’ve been supplying aluminum and other metals to customers in the San Francisco Bay Area for over two decades. We also ship to manufacturers and metalworkers nationwide with no minimum order quantities. We stock highly machinable aluminum 6061-T6 as well as other aluminum alloys and tempers, stainless steel, titanium, and many other metals and alloys.