The aluminum designation system commonly employs a four-character code to define the grades of cast and wrought aluminum alloys. In this four-character system, the first, third, and fourth characters are Arabic numerals, while the second is an uppercase English letter.  

These two types of aluminum alloys can be further subdivided into more categories based on their chemical composition and temper parameters.  

Alloying pure aluminum with other metals can yield a wide range of physical and mechanical properties. Based on the alloying elements, aluminum alloys are classified into two major categories: non-heat-treatable and heat-treatable alloys.  

Most aluminum standards define alloy grades as follows:  

- First character: Principal alloying element  

- Second character: Modification of the original pure aluminum or aluminum alloy  

- Third and fourth characters: Different alloys within the same group or indicating aluminum purity (the digits themselves carry no inherent meaning and are solely used to distinguish between materials).  

Wrought Aluminum Specifications:

Wrought aluminum alloys are classified as:  

1xxx – Pure aluminum (99.00% or higher);  

2xxx – Aluminum-copper alloys;  

3xxx – Aluminum-manganese alloys;  

4xxx – Aluminum-silicon alloys;  

5xxx – Aluminum-magnesium alloys;  

6xxx – Aluminum-magnesium-silicon alloys.  

Cast Aluminum Specifications:  

The standard and designation system for cast aluminum alloys are similar to those for wrought alloys. Cast aluminum alloy grades also consist of four characters, with the first indicating the principal alloying element. However, a decimal point is used between the third and fourth digits to clearly distinguish between castings (0) and ingots (1, 2).  

A letter prefix is used before the numerical designation to indicate the degree of modification to the original alloy or impurity limits. These letters start with A and proceed in alphabetical order, excluding I, O, Q, and X, where X is reserved for experimental alloys.  

Cast aluminum alloys are classified as:  

1xx.x – Pure aluminum (99.00% or higher);  

2xx.x – Aluminum-copper alloys;  

3xx.x – Aluminum-silicon + copper or magnesium alloys;  

4xx.x – Aluminum-silicon alloys;  

5xx.x – Aluminum-magnesium alloys;  

7xx.x – Aluminum-zinc alloys;  

8xx.x – Aluminum-tin alloys;  

9xx.x – Aluminum and other element alloys;  

6xx.x – Unused series.  

Temper Designation System for Aluminum Alloys:  

Temper is critically important in aluminum specifications as it significantly influences material properties. The temper designation system is based on the sequence of mechanical or thermal treatments applied. The temper code always follows the alloy designation, connected by a hyphen (e.g., 2014-T6, 3003-H14, 1350-H19 (extra hard)).  

The first character of the temper designation is an uppercase letter indicating the general heat treatment process:  

F – As-fabricated (no special treatment after shaping);  

O – Annealed;  

H – Strain-hardened;  

W – Solution heat-treated;  

T – Heat-treated to produce stable tempers.  

Note that the temper designations differ for non-heat-treatable and heat-treatable alloys, with specific meanings as follows.  

Non-Heat-Treatable Aluminum Alloys:  

The designation for non-heat-treatable alloys consists of the letter H followed by two or three digits. The first digit indicates the method of strain-hardening:  

H1 – Strain-hardened only;  

H2 – Strain-hardened and partially annealed;  

H3 – Strain-hardened and stabilized.  

The second digit indicates the degree of hardening:  

2 – 1/4 hard;  

4 – 1/2 hard;  

6 – 3/4 hard;  

8 – Full hard;  

9 – Extra hard.  

Based on their principal alloying elements, non-heat-treatable alloys primarily include the 1xxx, 3xxx, 4xxx, and 5xxx series.  

Heat-Treatable Aluminum Alloys (e.g., F, O, or T): 

The designation for heat-treatable alloys consists of the letter T followed by one or more digits. These digits represent the specific sequence of treatments applied to achieve stable tempers:  

T3 – Solution heat-treated and cold-worked;  

T4 – Solution heat-treated and naturally aged;  

T5 – Artificially aged only;  

T6 – Solution heat-treated and artificially aged; etc.  

Heat-treatable alloys primarily include the 2xxx, 6xxx, and 7xxx series.