Temper Designation System for Heat Treatable Aluminium Alloys

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Understanding Heat Treatment in Aluminium Alloys

Heat treating encompasses all controlled heating and cooling operations performed on metals or alloys in solid state for the purpose of altering their structure or properties. The thermal processes applied to ingots prior to working, during intermediate stages of fabrication, and after final working operations all fall under this comprehensive definition.

The properties and characteristics of wrought aluminium alloy products are significantly influenced by their complete thermal history, including the heating associated with hot working. However, the most important effects are those established by the final heat treating operations, which determine the ultimate performance characteristics of the finished product.

The ANSI H35.1(M) Temper Designation Framework

The temper designation system, according to ANSI H35.1(M), provides a standardized approach for all forms of wrought and cast aluminium and aluminium alloy products, except ingot. This system is fundamentally based on the sequences of basic treatments used to produce various tempers, ensuring consistency and clarity in material specification.

The temper designation follows the alloy designation, with the two components separated by a hyphen. This systematic approach allows engineers and manufacturers to quickly identify both the alloy composition and its thermal treatment history.

Basic Temper Designation Structure

Basic temper designations consist of letters that represent fundamental treatment categories. Subdivisions of these basic tempers are indicated by one or more digits following the letter when required. These digits designate specific sequences of basic treatments, but only operations recognized as significantly influencing the characteristics of the product are indicated in the designation system.

When variations of the same sequence of basic operations are applied to the same alloy, resulting in different characteristics, additional digits are added to the designation to maintain precise identification of the material condition.

The basic temper designations are as follows:

• F: As fabricated. Applies to wrought products that acquire some temper from shaping processes in which no special control is exercised over the amount of strain hardening or thermal treatment. For wrought products in this temper, there are no mechanical-property limits. Applies to castings in the as-cast condition if the alloy is also regularly produced in heat-treated tempers.
• O: Annealed (wrought products only). Applies to the softest temper of wrought products.
• W: Solution heat treated. An unstable temper applicable only to alloys that age at room temperature after solution heat treatment. This designation is specified only when the period of natural aging is indicated; for example: W (0.5 hr).
• T: Heat treated to produce stable tempers other than F or O. Applies to wrought and cast products that are heat treated, with or without supplementary cold working to produce stable tempers.

Heat-Treated Temper Classifications (T Designations)

The T designation is always followed by one or more digits, with numerals 1 through 10 indicating specific sequences of heat treatments. These numerical suffixes provide detailed information about the thermal processing history and resulting material properties, as shown in the table below.

An important consideration in T temper designations is that a period of natural aging may occur between the operations listed for tempers T3 through T10. Control of this natural aging period may be necessary to achieve the desired characteristics, particularly in applications requiring specific mechanical properties or dimensional stability.

Table 1. T1 to T10 designation system

Designation	Description
T1	Naturally aged to a substantially stable condition. Applies to products in which partial solution of the alloying elements is provided by elevated-temperature, rapid-cool fabrication.
T2	Annealed (cast products only). Designates a temper produced by a type of annealing treatment used to improve ductility and increase dimensional stability of castings.
T3	Solution heat treated, cold worked, and naturally aged to a substantially stable condition. Applies to products that are cold worked to improve strength, or in which the effect of cold work associated with flattening or straightening is recognized in applicable specifications. Different amounts of cold work are denoted by a second digit.
T4	Solution heat treated and naturally aged to a substantially stable condition. Applies to products that are not cold worked after solution heat treatment, or in which the effect of cold work associated with flattening or straightening may not be recognized in applicable specifications.
T5	Artificially aged only. Applies to products that are artificially aged after an elevated-temperature, rapid-cool fabrication process, such as casting or extrusion, to improve strength and/or dimensional stability.
T6	Solution heat treated and artificially aged. Applies to products not cold worked after solution heat treatment, or in which the effect of cold work associated with flattening or straightening may not be recognized in applicable specifications.
T7	Solution heat treated and averaged. Applies to products that are solution heat treated and artificially aged beyond the condition of maximum strength, to provide controlled special characteristics, such as dimensional stability, lower residual stresses, or improved resistance to corrosion.
T8	Solution heat treated, cold worked, and artificially aged. Applies to products that are cold worked to improve strength, or in which the effect of cold work associated with flattening or straightening is recognized in applicable specifications. Different amounts of cold work are denoted by a second digit.
T9	Solution heat treated, artificially aged, and cold worked. Applies to products that are cold worked as a final operation, to improve strength.
T10	Artificially aged and cold worked. Applies to products that are artificially aged after an elevated-temperature, rapid-cool fabrication process, such as casting or extrusion, and then cold worked to improve strength.

Stress-Relieved Temper Designations

The following designations involving additional digits are assigned to stress-relieved tempers of wrought products, where the letter x represents digits 3, 4, 6, or 8, whichever is applicable to the specific treatment sequence. This flexibility allows for precise specification of stress-relief treatments applied to various heat-treated conditions.

• Tx51: Stress relieved by stretching. Applies to products that are stress relieved by stretching the following amounts after solution heat treatment: plate - 0.5 to 3% permanent set; rod, bar and shapes -1 to 3% permanent set. This designation applies directly to plate and rolled or cold finished rod and bar. These products receive no further straightening after stretching. Additional digits are used in the designations for extruded rod, bar, shapes and tube as follows: Tx510 applies to products that receive no further straightening after stretching; Tx511 applies to products that receive minor straightening after stretching to comply with standard straightness tolerances.
• Tx52: Stress relieved by compressing. Applies to products that are stress relieved by compressing after solution heat treatment, to produce a nominal permanent set of 2.5%.
• Tx53: Stress relieved by thermal treatment.

User Heat-Treated Product Designations

Certain temper designations are assigned to wrought products that are heat treated by the user rather than the manufacturer. These designations provide guidance for end-users who perform additional thermal treatments to achieve specific application requirements. Examples include:

• T42: Solution heat treated
• T62: Solution heat treated and artificially aged

It should be noted that exceptions not conforming to standard definitions exist, such as 4032-T62 and 6101-T62, which represent special cases in the designation system developed for specific alloy and application combinations.