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SAE J993-2018: Standardized Alloy and Temper Designation Systems for Aluminum đ ī¸
SAE J993-2018 defines the numerical and temper designation systems for aluminum and aluminum alloys used in wrought and cast forms. This stabilized standard reflects mature technology and remains vital for consistent material specification in engineering applications.
Designation Systems for Wrought and Cast Aluminum
Wrought Aluminum Alloys
Wrought aluminum and its alloys are identified using a four-digit numerical designation. The first digit indicates the alloy group based on the major alloying element (see Table 1). The last two digits identify the specific alloy or, for the 1xxx series, indicate aluminum purity. The second digit shows modifications from the original alloy or impurity limits: 0 for the original alloy or no special impurity control, and 1–9 for successive modifications or controlled impurities.
| Series | Major Alloying Element |
|---|---|
| 1xxx | 99.00% minimum aluminum |
| 2xxx | Copper |
| 3xxx | Manganese |
| 4xxx | Silicon |
| 5xxx | Magnesium |
| 6xxx | Magnesium and Silicon |
| 7xxx | Zinc |
| 8xxx | Other element |
| 9xxx | Unused series |
Experimental alloys carry the prefix X, which is dropped upon formal registration. National variations of wrought alloys are indicated by a serial letter before the numerical designation (e.g., A1xxx).
Cast Aluminum Alloys and Ingot
Cast aluminum alloys use a four-digit designation followed by a decimal point and a final digit. The first digit indicates the alloy group (see Table 2). The second two digits identify the alloy or, for the 1xx.x series, indicate purity. The last digit determines product form: .0 for castings, .1 for ingot with composition limits matching the casting, and .2 for ingot with slightly different limits. Alloy modifications are shown by a preceding serial letter (e.g., A356.0).
| Series | Major Alloying Element |
|---|---|
| 1xx.x | 99.00% minimum aluminum |
| 2xx.x | Copper |
| 3xx.x | Silicon, with added copper and/or magnesium |
| 4xx.x | Silicon |
| 5xx.x | Magnesium |
| 7xx.x | Zinc |
| 8xx.x | Tin |
| 9xx.x | Other element |
Note: This cast designation system is applicable to Aluminum Association (AA) and ANSI systems; it is not yet used for some SAE cast aluminum alloys.
🔍 Design Insight: Understanding the designation system allows engineers to accurately select alloys and tempers for manufacturing processes. The clear structure reduces errors in material ordering and heat treatment specifications. For example, confusing a wrought alloy (e.g., 6061) with a cast alloy (e.g., A356.0) can lead to improper applications. Always verify the decimal point for cast products and note that the second digit in non-1xxx wrought series indicates modification history, not composition.
Temper Designation System
The temper designation follows the alloy number separated by a hyphen and indicates the treatment sequence used to achieve the material’s properties. Basic temper letters include F (as fabricated), O (annealed), H (strain hardened), and T (thermally treated). Subdivisions add digits, such as T6, T651, or H14. The system applies to all wrought and cast products except ingot.
Frequently Asked Questions
What do the last two digits in the 1xxx series indicate?
In the 1xxx series, the last two digits represent the minimum aluminum percentage to the nearest 0.01%. For example, alloy 1050 has a minimum of 99.50% aluminum.
How are alloy modifications indicated for wrought and cast alloys?
For wrought alloys, the second digit indicates modifications: 0 for original, 1–9 for successive changes. For cast alloys, a serial letter (A, B, etc.) precedes the numerical designation.
What does the prefix X mean in an alloy number?
The prefix X indicates an experimental alloy. It is used temporarily and is removed once the alloy is fully registered and no longer experimental.
How are castings and ingot differentiated in cast alloy designations?
The digit after the decimal point indicates product form: .0 for castings, .1 and .2 for ingot with different composition limit requirements.
Common Mistakes: Ensure the decimal point is not omitted in cast alloy designations (e.g., write 356.0, not 3560). Do not assume the last two digits in non-1xxx series indicate purity — they are arbitrary identifiers. For cast alloys, the product form digit is critical for material specification.
For full details, refer to SAE J993-2018, which provides comprehensive guidance on alloy and temper designation systems for aluminum.
