For most people aluminum is simply aluminum, a silvery white metal that is lightweight 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 certain properties and minimize others. The different aluminum alloys are then given a heat treatment to further enhance their strength and corrosion resistance. The combination of these additional metals and treatments results in different aluminum grades and properties.
The difference in these grades are what makes the difference between sophisticated jet aircraft, and the beverage container crushed on the forehead of a youth trying to prove something. These differences are worth knowing, and exploring in depth. There are differences between wrought aluminum alloy and cast aluminum alloy grades.
Aluminum Grades and Properties
How cast aluminum alloys are designated depends on how they are formed. There are different designations for wrought—pure aluminum that is drawn, rolled, or otherwise mechanically formed—and cast—molded while molten. These designations are not an exact science. The categories are very broad and always expanding. New formulations are periodically developed, and are given a designation based on the additional metals added to the formulation. One logical number set—the 6000—in the sequence for cast aluminums is skipped over entirely due to 6061, 6062, and 6063 wrought aluminums being so widely used. In structural use and machining 6061 aluminum is effectively the default.
|Aluminum Alloy Designations
|Wrought Aluminum Alloys
|Cast Aluminum Alloys
|99% Pure Aluminum
|99% Pure Aluminum
|Silicon Plus Copper and/or Magnesium
|Magnesium and Silicon
|*6XX.X series not used for cast aluminums
In addition to these series there are additional considerations. Tempers that harden the metal through the use of heat, 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.
|As fabricated—no additional treatments
|Annealed-heated to increase ductility and improve dimensional stability
|Strain Hardened—Strained to produce plastic deformations “prestressed” and strengthen the metal. Additional treatments may be applied
H2-Strain Hardened and Annealed
H3-Strain hardened and stabilized
H4-Strain Hardened and coated
|Solution Heat Treated—Chemically treated to induce tempering at room temperature. Tempering may be unstable.
|Thermally Treated—Tempered by elevated heat in order to produce a stable temper.
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.
allowed to cool naturally from elevated temperatures
Maintained at elevated temperatures for an extended period of time
Overaged, maintained at elevated temperatures for an extended period to work out instabilities potentially sacrificing strength.
Not only are the differences between series substantial. The addition of 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. Understanding all the difference between the different types of aluminum alloys is important. However, most work with aluminum uses a relatively few aluminum grades that have a good general use profile.
The Common Aluminum Grades for Daily Work
One of the reasons that pure aluminum is just aluminum for most people is that the difference between certain grades of aluminum only really comes up in highly specialized applications. If you work with aluminum as an architectural welder T6-6061 aluminum is going to be the aluminum grade that you see most often. Likewise if you are a machinist. The difference between grades isn’t really going to come up unless there is an issue of some type. A job where the typical aluminum grade that is commonly used won’t suffice.
In machining an example is found in high precision parts like making the molds used in injection and vacuum forming molds for plastic. While 6061 aluminum does an admirable job in most machining tasks it does suffer a fault as a result of 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. In this example switching to cast aluminum provides a solution. As it is a molded product it doesn’t have the same internal forces that wrought products do, and can be machined more accurately without the risk of distortion.
Knowing aluminum grades and properties matter when these issues arise. As is knowing where the correct aluminum grade with the needed properties can be found. A good aluminum, and metal supplier overall, is the key to finding the right metals including the aluminum grades and properties that you need to complete tight tolerance and high specification jobs.
Industrial Metal Service is a nationwide aluminum supplier for machinists, welders, and fabricators with an extensive inventory of 6061 aluminum and cast aluminums like Alca 5 and ACP 5080. Available in both standard sizes.