The properties and characteristics of wrought aluminium alloy products are significantly influenced by their complete thermal history, with the most critical effects established by final heat treating operations. Heat treating encompasses all controlled heating and cooling operations performed on metals in solid state to alter structure or properties. The temper designation system, according to ANSI H35.1(M), applies to all forms of wrought and cast aluminium alloys except ingot, based on sequences of basic treatments used to produce various tempers. This system uses letter-based basic temper designations followed by digits that indicate specific treatment sequences, with the T designation representing heat-treated conditions through various controlled thermal processes that significantly influence product characteristics.
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 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 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:
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. |
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.
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:
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.
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