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.

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 heating
applications 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.

EN Standards for Aluminium

Standard Scope

EN485-1

Technical conditions for inspection and delivery

EN485-2

Mechanical properties

EN485-3

Tolerances for hot rolled materials

EN485-4

Tolerances for cold rolled materials

EN515

Temper designations

EN573-1

Numerical alloy designation system

EN573-2

Chemical symbol designation system

EN573-3

Chemical compositions

EN573-4

Product forms in different alloys

The EN 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.

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