Aluminium Alloy Specifications
There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. The section below describes the system for wrought alloys. Cast alloys have similar designations and use a five digit system.
Designations for Wrought Aluminium Alloys
Aluminium is most commonly alloyed with copper, zinc, magnesium, silicon, manganese and lithium. Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities.
There are over 300 wrought alloys with 50 in common use. They are normally identified by a four figure system which originated in the USA and is now universally accepted. Table 1 describes the system for wrought alloys. Cast alloys have similar designations and use a five digit system.
- Alloying Element None (99%+ Aluminium) - 1XXX
- Alloying Element Copper - 2XXX
- Alloying Element Manganese - 3XXX
- Alloying Element Silicon - 4XXX
- Alloying Element Magnesium - 5XXX
- Alloying Element Magnesium + Silicon - 6XXX
- Alloying Element Zinc - 7XXX
- Alloying Element Lithium/Other - 8XXX
For unalloyed wrought aluminium alloys designated 1XXX, the last two digits represent the purity of the metal. They are the equivalent to the last two digits after the decimal point when aluminium purity is expressed to the nearest 0.01 percent. The second digit indicates modifications in impurity limits. If the second digit is zero, it indicates unalloyed aluminium having natural impurity limits and 1 through 9, indicate individual impurities or alloying elements.For the 2XXX to 8XXX groups, the last two digits identify different aluminium alloys in the group. The second digit indicates alloy modifications. A second digit of zero indicates the original alloy and integers 1 to 9 indicate consecutive alloy modifications.
The only exception to this is where a customer orders a grade of material for which the applicable Chinese, British, European or International material standard requires the level of one or more of these substances to exceed the limits specified in GB/T 26572. In such cases, the material will contain a value of each such substance in line with the requirements of the relevant material standard.
Physical Properties
Density
Aluminium has a density around one third that of steel or copper making it one of the lightest commercially available metals. The resultant high strength to weight ratio makes it an important structural material allowing increased payloads or fuel savings for transport industries in particular.
Strength
Pure aluminium doesn’t have a high tensile strength. However, the addition of alloying elements like manganese, silicon, copper and magnesium can increase the strength properties of aluminium and produce an alloy with properties tailored to particular applications. Aluminium is well suited to cold environments. It has the advantage over steel in that its’ tensile strength increases with decreasing temperature while retaining its toughness. Steel on the other hand becomes brittle at low temperatures.
Corrosion Resistance
When exposed to air, a layer of aluminium oxide forms almost instantaneously on the surface of aluminium. This layer has excellent resistance to corrosion. It is fairly resistant to most acids but less resistant to alkalis.
Thermal Conductivity
The thermal conductivity of aluminium is about three times greater than that of steel. This makes aluminium an important material for both cooling and heatingapplications such as heat-exchangers. Combined with it being non-toxic this property means aluminium is used extensively in cooking utensils and kitchenware.
Electrical Conductivity
Along with copper, aluminium has an electrical conductivity high enough for use as an electrical conductor. Although the conductivity of the commonly used conducting alloy (1350) is only around 62% of annealed copper, it is only one third the weight and can therefore conduct twice as much electricity when compared with copper of the same weight.
Reflectivity
From UV to infra-red, aluminium is an excellent reflector of radiant energy. Visible light reflectivity of around 80% means it is widely used in light fixtures. The same properties of reflectivity makes aluminium ideal as an insulating material to protect against the sun’s rays in summer, while insulating against heat loss in winter.
Typical Properties of Aluminium
| Property | Value |
| Atomic Number | 13 |
| Atomic Weight (g/mol) | 26.98 |
| Valency | 3 |
| Crystal Structure | FCC |
| Melting Point (oC) | 660.2 |
| Boiling Point (oC) | 2480 |
| Mean Specific Heat (0-100oC) (cal/g.oC) | 0.219 |
| Thermal Conductivity (0-100oC) (cal/cms.oC) | 0.57 |
| Co-efficient of Linear Expansion (0-100oC) (x10-6/oC) | 23.5 |
| Electrical Resistivity at 20oC μΩ.cm | 2.69 |
| Density (g/cm3) | 2.6898 |
| Modulus of Elasticity (GPa) | 68.3 |
| Poissons Ratio | 0.34 |
Mechanical Properties
Aluminium can be severely deformed without failure. This allows aluminium to be formed by rolling, extruding, drawing, machining and other mechanical processes. It can also be cast to a high tolerance. Alloying, cold working and heat-treating can all be utilised to tailor the properties of aluminium. The tensile strength of pure aluminium is around 90 MPa but this can be increased to over 690 MPa for some heat-treatable alloys.
Mechanical Properties of Selected Aluminium Alloys
| Alloy | Temper | Proof Stress 0.2% (MPa) | Tensile Strength (MPa) | Shear Strength (MPa) | Elongation A5 (%) | Hardness Vickers (HV) |
| AA1050A | H12 | 85 | 100 | 60 | 12 | 30 |
| H14 | 105 | 115 | 70 | 10 | 36 | |
| H16 | 120 | 130 | 80 | 7 | - | |
| H18 | 140 | 150 | 85 | 6 | 44 | |
| O | 35 | 80 | 50 | 42 | 20 | |
| AA2011 | T3 | 290 | 365 | 220 | 15 | 100 |
| T6 | 300 | 395 | 235 | 12 | 115 | |
| AA3103 | H14 | 140 | 155 | 90 | 9 | 46 |
| O | 45 | 105 | 70 | 29 | 29 | |
| AA4015 | O | 45 | 110-150 | - | 20 | 30-40 |
| H12 | 110 | 135-175 | - | 4 | 45-55 | |
| H14 | 135 | 160-200 | - | 3 | - | |
| H16 | 155 | 185-225 | - | 2 | - | |
| H18 | 180 | 210-250 | - | 2 | - | |
| AA5083 | H32 | 240 | 330 | 185 | 17 | 95 |
| O/H111 | 145 | 300 | 175 | 23 | 75 | |
| AA5251 | H22 | 165 | 210 | 125 | 14 | 65 |
| H24 | 190 | 230 | 135 | 13 | 70 | |
| H26 | 215 | 255 | 145 | 9 | 75 | |
| O | 80 | 180 | 115 | 26 | 46 | |
| AA5754 | H22 | 185 | 245 | 150 | 15 | 75 |
| H24 | 215 | 270 | 160 | 14 | 80 | |
| H26 | 245 | 290 | 170 | 10 | 85 | |
| O | 100 | 215 | 140 | 25 | 55 | |
| AA6063 | O | 50 | 100 | 70 | 27 | 85 |
| T4 | 90 | 160 | 11 | 21 | 50 | |
| T6 | 210 | 245 | 150 | 14 | 80 | |
| AA6082 | O | 60 | 130 | 85 | 27 | 35 |
| T4 | 170 | 260 | 170 | 19 | 75 | |
| T6 | 310 | 340 | 210 | 11 | 100 | |
| AA6262 | T6 | 240 | 290 | - | 8 | - |
| T9 | 330 | 360 | - | 3 | - | |
| AA7075 | O | 105-145 | 225-275 | 150 | 9 | 65 |
| T6 | 435-505 | 510-570 | 350 | 5 | 160 |
Aluminium Standards
The old BS1470 standard has been replaced by nine EN standards. The EN standards are given in the table below.
CN Standards for Aluminium
| Standard | Scope |
| GB/T 3880.1 | Technical conditions for delivery of wrought aluminium and aluminium alloy plates, sheets and strips (general inspection, delivery requirements). |
| GB/T 3880.2 | Mechanical properties of wrought aluminium and aluminium alloy plates, sheets and strips. |
| GB/T 3880.3 | Dimensions and tolerances for wrought aluminium and aluminium alloy plates, sheets and strips (covers thickness, width, length and form tolerances for hot- and cold-rolled products in one standard, instead of EN 485-3 / 485-4 split). |
| GB/T 16475 (commonly used) | Temper designations for wrought aluminium and aluminium alloys (Chinese temper system corresponding to T4, T6, H14, etc.; similar role to EN 515). |
| GB/T 3190 | Chemical composition of wrought aluminium and aluminium alloys (defines alloy series such as 1050, 3003, 5052, 6061, 7075, etc.; functionally covers the “chemistry” part of EN 573-3). |
- The CN standards differ from the old standard, BS1470 in the following areas:
- Chemical compositions – unchanged.
- Alloy numbering system – unchanged.
- Temper designations for heat treatable alloys now cover a wider range of special tempers. Up to four digits after the T have been introduced for nonstandard applications (e.g. T6151).
- Temper designations for non heat treatable alloys – existing tempers are unchanged but tempers are now more comprehensively defined in terms of how they are created. Soft (O) temper is now H111 and an intermediate temper H112 has been introduced. For alloy 5251 tempers are now shown as H32/H34/H36/H38 (equivalent to H22/H24, etc). H19/H22 & H24 are now shown separately.
- Mechanical properties – remain similar to previous figures. 0.2% Proof Stress must now be quoted on test certificates.
- Tolerances have been tightened to various degrees.
Heat Treatment
- A range of heat treatments can be applied to aluminium alloys:
- Homogenisation – the removal of segregation by heating after casting.
- Annealing – used after cold working tos often work-hardening alloys (1XXX ,3XXX and 5XXX).
- Precipitation or age hardening (alloys 2XXX, 6XXX and 7XXX).
- Solution heat treatment before ageing of precipitation hardening alloys.
- Stoving for the curing of coatings
- After heat treatment a suffix is added to the designation numbers.
- The suffix F means “as fabricated”.
- O means “annealed wrought products”.
- T means that it has been “heat treated”.
- W means the material has been solution heat treated.
- H refers to non heat treatable alloys that are “cold worked” or “strain hardened”.
- The non-heat treatable alloys are those in the 3XXX, 4XXX and 5XXX groups.
Heat Treatment Designations for Aluminium & Aluminium Alloys
| Term | Scope |
| T1 | Cooled from an elevated temperature shaping process and naturally aged. |
| T2 | Cooled from an elevated temperature shaping process cold worked and naturally aged. |
| T3 | Solution heat-treated cold worked and naturally aged to a substantially stable condition. |
| T4 | Solution heat-treated and naturally aged to a substantially stable condition. |
| T5 | Cooled from an elevated temperature shaping process and then artificially aged. |
| T6 | Solution heat-treated and then artificially aged. |
| T7 | Solution heat-treated and overaged/stabilised. |
Work Hardening
The non-heat treatable alloys can have their properties adjusted by cold working. Cold rolling is a typical example.
These adjusted properties depend upon the degree of cold work and whether working is followed by any annealing or stabilising thermal treatment.
Nomenclature to describe these treatments uses a letter, O, F or H followed by one or more numbers. As outlined in the table below, the first number refers to the worked condition and the second number the degree of tempering.
Non Heat Treatable Alloy Designations
| Term | Description |
| H1X | Work hardened |
| H2X | Work hardened and partially annealed |
| H3X | Work hardened and stabilised by low temperature treatment |
| H4X | Work hardened and stoved |
| HX2 | Quarter hard - degree of working |
| HX4 | Half hard - degree of working |
| HX6 | Three quarter hard - degree of working |
| HX8 | Full hard - degree of working |
Temper Codes for Plate
| Code | Description |
| H112 | Alloys that have some tempering from shaping but do not have special control over the amount of stain hardening or thermal treatment. Some strength limits apply. |
| H321 | Strain hardened to an amount less than required for a controlled H32 temper. |
| H323 | A version of H32 that has been specially fabricated to provide acceptable resistance to stress corrosion cracking. |
| H343 | A version of H34 that has been specially fabricated to provide acceptable resistance to stress corrosion cracking. |
| H115 | Armour plate. |
| H116 | Special corrosion resistant temper. |
