Aluminum Grades And Properties

For most people, aluminum is simply aluminum, a silvery-white lightweight metal used in aircraft and beverage cans. This is, however, a mostly inaccurate assessment. Metals are never simply one metal. They are almost always alloyed with other metals to enhance mechanical properties and minimize others. The different grades of aluminum alloys are then given a heat treatment to improve their strength and excellent corrosion resistance further. Combining these additional metals and treatments results in different aluminum grades and properties with varying levels of corrosion resistance.

The difference in these grades distinguishes sophisticated jet aircraft from the beverage container crushed on the forehead of a youth trying to prove something. These differences are worth knowing and exploring in depth. The corrosion resistance in different aluminum grades plays a significant role in their applications, including marine applications and aerospace applications. There are differences between wrought aluminum alloy and cast aluminum alloy grades, exhibiting good corrosion resistance characteristics.

Understanding the nuances of heat treatment and corrosion resistance in these aluminum alloys is crucial for their effective use in various industries. Heat treatment is important in developing the desired properties of aluminum alloys, including their corrosion resistance and mechanical strength. This is especially vital in marine and aerospace applications, where durability and performance are paramount.

Aluminum Alloy Designations and Temper Types

The designation of cast alloys depends on their formation process. Different designations exist for wrought alloys—pure aluminum drawn, rolled, or otherwise mechanically formed—and cast alloys—molded while molten. These designations are not an exact science. The categories are very broad and constantly expanding. New formulations, including heat-treatable alloys, are periodically developed and designated based on the additional metals added to enhance corrosion resistance. The primary alloying element in these formulations often dictates the specific properties of the alloy, including its corrosion resistance and strength-to-weight ratio.

One logical number set—the 6000—in the sequence for cast aluminum is skipped over entirely because 6061, 6062, and 6063 wrought aluminum are so commonly used. In structural use and machining, 6061 aluminum, known for its corrosion resistance, excellent strength-to-weight ratio, and heat-treatable, is the default. The development of silicon alloys and magnesium alloys continues to expand the range of available aluminum alloys, offering improved performance in various applications, including the automobile industries.

The international alloy designation system plays a crucial role in these classifications, and understanding the international alloy designation system is essential for proper identification. Additionally, developing a high mechanical strength alloy with good corrosion resistance is often a goal in these new formulations to meet specific application needs.

Aluminum Alloy Designations
Wrought Aluminum Alloys		Cast Aluminum Alloys
Series	Alloying Element	Series	Alloying Element
1XXX	99% Pure Aluminum	1XX.X	99% Pure Aluminum
2XXX	Copper	2XX.X	Copper
3XXX	Manganese	3XX.X	Silicon Plus Copper and/or Magnesium
4XXX	Silicon	4XX.X	Silicon
5XXX	Magnesium	5XX.X	Magnesium
6XXX	Magnesium and Silicon	7XX.X	Zinc
7XXX	Zinc	8XX.X	Tin
8XXX	Other Elements	9XX.X	Other Elements
*6XX.X series not used for cast aluminum

In addition to these series, there are additional considerations. Tempers that harden the metal through heat treatment, chemicals, and even stressing the material. Alternatively, there are treatments that technically soften the metal but improve its ductility and flexibility or its thermal or dimensional stability over time.

Temper Type	Description	Subtypes	Subdivision
F	As fabricated—no additional treatments	NA	NA
O	Annealed-heated to increase ductility and improve dimensional stability	NA
H	Strain Hardened—Strained to produce plastic deformations “prestressed” and strengthen the metal. Additional treatments may be applied	H1-Strain Hardened H2-Strain Hardened and Annealed H3-Strain hardened and stabilized H4-Strain Hardened and coated	HX2-1/4 Hard HX4-1/2 Hard HX6-¾ Hard HX8-Full Hard Hx9-Extra Hard
W	Solution Heat Treated—Chemically treated to induce tempering at room temperature. Tempering may be unstable.
T	Thermally Treated—Tempered by elevated heat to produce a stable temper.	T1-Naturally aged T2-Cold worked T3-Solution treated, cold worked, naturally aged T4-Solution heat-treated and naturally aged T5-Artificially aged after shaping and cooling T6-Solution heat-treated and artificially aged T7-Solution heat-treated and stabilized T8-Solution heat-treated, cold-worked, and artificially aged T9-Solution heat-treated, artificially aged, and cold-worked T10-Cold-worked after cooling from hot shaping and then artificially aged.	Naturally Aged— allowed to cool naturally from elevated temperatures Artificially Aged— Maintained at elevated temperatures for an extended period of time Stabilized— Overaged, maintained at high temperatures for an extended period to work out instabilities potentially sacrificing strength.

Not only are the differences between aluminum alloy series substantial, but adding a temper to these aluminum alloys can also substantially change the mechanical properties of an alloy type in a series. The 6061 aluminum properties for naturally aged T4 aluminum are quite different from solution-treated and artificially aged T6 aluminum grade.

It is important to understand all the differences between the different grades of aluminum alloys. However, most aluminum work typically involves a few alloys with a good general-use profile.

The Common Aluminum Grades for Daily Work

One reason pure aluminum is just aluminum for most people is that the difference between a specific aluminum grade only really comes up in highly specialized applications. If you work with aluminum for architectural applications, T6-6061 aluminum, known for its excellent corrosion resistance and thermal conductivity, is going to be the aluminum grade that you see most often. 

Likewise, if you are a machinist, the excellent corrosion resistance and thermal conductivity of 6061 aluminum make it a frequent choice. The difference between aluminum alloys isn’t really going to come up unless there is an issue—a job where the typical aluminum grade that is commonly used won’t suffice.

In machining, an example is found in high-precision parts, such as making the molds used in injection and vacuum forming molds for plastic. While 6061 aluminum does an admirable job in most machining tasks, it suffers a fault due to the forging process. It creates internal tensions that are balanced within the material. When one side is removed during machining, this balance is altered, and the piece can become distorted. This is an issue in most applications, but especially big when the part that is being machined will directly affect the tolerances of additional parts.

There are other, even more demanding applications, such as in the aerospace industry. In this example, switching to cast aluminum, which possesses excellent corrosion resistance and superior thermal conductivity, provides a solution. As it is a molded product, it doesn’t have the same internal forces that wrought products do, and it can be machined more accurately without the risk of mechanical deformation. The excellent corrosion resistance of cast aluminum also ensures durability in various environments. Thus, the excellent corrosion resistance and thermal conductivity of aluminum alloys are significant factors in their selection for specialized applications, such as marine applications and aerospace applications.

These properties also benefit the automotive engineering field, ensuring high performance and longevity in vehicle components and effective thermal conductivity to manage heat dissipation in engines and other critical parts.

Knowing each aluminum grade and its properties matters when these issues arise, as does knowing where the correct aluminum alloy with the needed properties can be found. A good aluminum and metal supplier is the key to finding the right metals, including the aluminum grades and properties that you need to complete tight tolerance and high-spec jobs.

Industrial Metal Service is a nationwide aluminum supplier for machinists, welders, and fabricators with an extensive inventory of 6061 aluminum and cast aluminum such as Alca 5 and ACP 5080. Available in both standard sizes.