Aluminum Alloy Tempers
1Key Takeaways
The purpose of this SAE Aerospace Standard (AS) is to provide a description of the temper nomenclature system for aluminum alloys used in the aerospace industry by combining information from different sources for the benefit of the user.
2Expert Interpretation
This article provides an in-depth interpretation of the SAE AS1990D aerospace standard for aluminum alloy condition codes, detailing the meanings of the five basic conditions (F/O/H/W/T) and their sub-codes. It also includes a complete classification system for strain hardening and heat treatment processes, providing professional technical guidance for aerospace material selection and process development.
SAE AS1990D Standard Overview and Technical Background
SAE AS1990D, "Aluminum Alloy Condition Designations," is a key material standard specification for the aerospace industry. The standard was declared stabilized in 2016, meaning its technical content will no longer be updated, but it remains a reference for the industry. The standard primarily defines a condition designation system for aluminum alloys, providing a unified technical language for material selection, process development, and quality control of aluminum alloys used in aerospace applications.
Standard Status Evolution and Technology Replacement
The AS1990D standard has undergone a complete technical lifecycle, from initial publication in 1990, revisions in 2003, reaffirmation in 2013, to stabilization in 2016. The primary reason for stabilization is that equivalent technical requirements have been incorporated into other standards, particularly the American National Standards ANSI H35.1/H35.1M. When using this standard, users should refer to the relevant engineering organization's opinions on any issues, including exceptions listed in the certification.
| Standard Version | Release Status | Technical Update Content | Applicability |
|---|---|---|---|
| AS1990D (2016) | Stabilized | Last technical update in January 2003 | Historical reference, not recommended for new projects |
| ANSI H35.1/H35.1M | Currently valid | Includes equivalent technical requirements | Recommended for new procurement projects |
| EN 515 | European Standard | Forged Product Condition Code | Applicable to European Projects |
| ISO 2107 | International Standard | Forged Product Condition Code | Applicable to International Projects |
Details of the Aluminum Alloy Condition Code System
The aluminum alloy condition code system is based on rules established by The Aluminum Association and uses codes to represent the basic sequence of processing steps that a material undergoes, including mechanical treatment, heat treatment, or thermo-mechanical treatment.
Five basic state codes
| State code | Meaning | Application range | Characteristics description |
|---|---|---|---|
| F | Assembly state | All products | No special thermal control or strain hardening, no mechanical property restrictions for forgings |
| O | Annealed state | All products | Obtain the lowest strength state, improve ductility and dimensional stability |
| H | Strain hardening | Forgings only | |
| T | Heat treatment | All products | Stable state achieved by heat treatment, which may be supplemented by strain hardening |
| W | Solution treatment | Specific alloys | Unstable state, only applicable to alloys naturally aged at room temperature |
| T | Heat treatment | All products | Stable state achieved by heat treatment, which may be supplemented by strain hardening |
Subdivision rules of H condition code
The H condition code is followed by two or more digits, the first digit indicates the specific combination of basic operations:
| Code | Treatment process | Technical features | Application Examples |
|---|---|---|---|
| H1X | Strain hardening only | No supplementary heat treatment, the number indicates the degree of strain hardening | 5083-H116 marine aluminum alloy plate |
| H2X | Strain hardening + partial annealing | First strain hardening and then partial annealing to the required strength | 3003-H24 heat exchanger fins |
| H3X | Strain hardening + stabilization | Mechanical properties stabilized by low temperature heat treatment | 5052-H32 automotive body plate |
| H4X | Strain Hardened + Painted | Paint Cured During Thermal Operation | Architectural Coated Aluminum Sheet |
The second digit indicates the degree of strain hardening: the number 8 indicates the ultimate tensile strength achieved by approximately 75% cold reduction, the number 4 indicates a value intermediate between the O and 8 tempers, the number 2 indicates a value intermediate between the O and 4 tempers, and the number 6 indicates a value intermediate between the 4 and 8 tempers. The number 9 indicates a strength exceeding the 8 temper by at least 2.0 ksi.
Detailed classification of T state code
T state code represents a specific basic processing sequence through numbers 1-10:
| Code | Processing sequence | Process characteristics | Typical application |
|---|---|---|---|
| T1-T4 | Natural aging series | Achieving basic stable state through natural aging | 2024-T3 aviation structural parts |
| T5 | High temperature forming + artificial aging | Direct artificial aging after cooling from high temperature forming | Die castings, such as A380-T5 |
| T6 | Solution treatment + artificial aging | The most commonly used heat treatment strengthening process | 6061-T6 structural profiles |
| T7 | Solution treatment + overaging | Exceeding the peak strength point to control specific properties | 7075-T73 high stress corrosion resistance parts |
| T8-T10 | Combined treatment series | Complex process combining cold working and heat treatment | High strength fasteners |
Guide to the Application of Aluminum Alloy Tempers for Aerospace
Chapter 5 of the standard lists in detail the alloy-temper combinations of interest to the aerospace industry, including specific treatment process codes for castings and forgings:
| Alloy Series | Typical Tempers | Treatment Process | Aerospace Applications |
|---|---|---|---|
| 2xxx Series | 2024-T3, 2014-T6 | Solution Treatment + Cold Working + Natural Aging | Aircraft Skin, Structural Parts |
| 7xxx Series | 7075-T6, 7075-T73 | Solution treatment + artificial aging/overaging | High-strength structural parts, landing gear |
| Casting alloys | A356-T6, A357-T6 | Solution treatment + artificial aging | Engine components, cabin structures |
| 5xxx series | 5083-H116, 5086-H32 | Strain hardening + stabilization | Ship structures, fuel tanks |
Standard implementation recommendations and precautions
Although AS1990D has been stabilized, the following points should still be noted in actual applications:
Material Selection Recommendations
For new project procurement, it is recommended to give priority to the ANSI H35.1/H35.1M standard, which contains equivalent and updated technical requirements. For existing projects or historical data inquiries, AS1990D can still be used as a reference.
Certification and Exceptions
Users should be aware of possible exceptions to the standard, which are usually clearly listed in the certification documents. The purchaser may represent a sub-supplier rather than the relevant engineering organization. In this case, special attention should be paid to the accuracy of the technical requirements.
Application of Special Condition Codes
The standard appendix details the marking method for three-digit H condition, additional digits for T condition, and unregistered condition codes. For example:
- H116: Applicable to 5xxx series alloys with a magnesium content ≥3%, with specific exfoliation corrosion resistance
- T73/T74/T76: Conditions with varying degrees of overaging, achieving a balance between strength and corrosion resistance
- Txx2: Indicates a heat treatment condition performed by the user
Technical Document Update Requirements
Since this standard has been stabilized, relevant technical documents should clearly indicate the applicable status of the standard to avoid directly citing stabilized standard requirements in new projects. It is recommended to establish a standard version management mechanism to ensure the use of the latest valid standard version.
Conclusion
SAE AS1990D provides a complete classification system for the condition codes of aerospace aluminum alloy materials. Although it has now been stabilized, its technical content still has important reference value. A thorough understanding of the meaning of the status codes and their corresponding treatment processes is crucial for selecting the right materials, developing process specifications, and ensuring product quality. In practical applications, updated standards such as ANSI H35.1/H35.1M should be combined to form a complete technical requirements system.