Aluminium
Property
Constituents
Aluminium, by reason of its chemical reactivity, is not found in its pure state, but in combination with other elements. It is the most common metallic element in the earth’s crust which contains approximately 15% of Al2O3 (8% aluminium).
Commercial aluminium is generally 99.0% – 99.6% pure.
Typical composition of commercially pure aluminium:
|
Al
|
Si
|
Fe
|
Cu
|
Mn
|
Mg
|
Zn
|
Ti
|
| 99.5% | 0.2% | 0.2 % max | 0.04% max | 0.03 % max | 0.03 % max | 0.03 % max | 0.03 % max |
Alloy Types
Aluminium is seldom used in its pure form but is normally alloyed with small proportion of other elements. Typical of those are:
- Copper
- Manganese
- Silicon
- Magnesium
- Zinc
In the alloying furnace, the aluminum ingot is melted, and mixed with alloying metals like Magnesium, silica, copper, etc to form an aluminium alloy which offers a wide range of specific material properties. The physical properties of the alloy are very much determined by the alloy content. For example:
- Manganese offers good corrosion resistance
- Magnesium is good for welding applications
- Copper yields excellent machinability
- Zinc tends to offer very high strength
Classification
According to BS 1490, casting alloys are designated by numbers in sequence of development which would be preceded by the letters LM (light metal), i.e. LM6.
In US, 4 digit system is used:
| First digit | Major alloying element |
| 1xx.x | Pure aluminium (> 99%) |
| 2xx.x | Copper |
| 3xx.x | Silicon + copper and/ or magnesium |
| 4xx.x | Silicon |
| 5xx.x | Magnesium |
| 6xx.x | Unused series |
| 7xx.x | Zinc |
| 8xx.x | Tin |
| 9xx.x | Other elements |
Examples of 4 digits numerical alloy nomenclature system:
| . | Alphanumerical system | Major alloying elements |
| 3103 | Al Mn1 | Manganese |
| 5083 | Al Mg 4.5Mn | Magnesium |
| 6082 | Al Si1 Mg Mn | Magnesium and silicon. |
In Asia, the most popular 6xxx series alloys are 6xxx Series Aluminum Extrusion Alloys:
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Typical Minimum Mechanical Properties of 6xxx Series
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Alloy
|
Properties
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Major Alloying Elements %
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Temper
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Ultimate Tensile Strength PSI
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Yield Tensile Strength PSI
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Elongation In 2 Inches%
|
|
6063 |
Good corrosion resistance, finishing response, weldability, machinability, formability
|
0.20 – 0.60 Si Max 0.35 Fe 0.45 – 0.90 Mg |
T1 T4 T5 T6 |
16000 18000 21000 30000 |
8000 9000 15000 25000 |
12 14 8 10 |
|
6060 |
Great balance of extrudability and mechanical properties. Provides good surface finishes, readily welded, good corrosion resistance and forms well.
|
0.30 – 0.60 Si 0.10 – 0.30 Fe 0.35 – 0.60 Mg |
T51 T61 |
22000 30000 |
16000 25000 |
8 8 |
|
6463 |
Produces a bright, mirror-like, high quality finish, good machinability and formability
|
0.20 – 0.60 Si Max 0.15 Fe Max 0.20 Cu 0.45 – 0.65 Mg |
T1 T5 T6 |
17000 22000 30000 |
9000 16000 25000 |
12 8 10 |
|
6061 |
Excellent strength, corrosion resistance and machinabilty, poor finishing response, good weldability and formability
|
0.40 – 0.80 Si Max 0.70 Fe 0.80 – 1.20 Mg |
T1 T4 T5 T6 |
26000 26000 35000 38000 |
14000 16000 30000 35000 |
16 16 8 10 |
|
6005 |
Excellent extrudability and strength, low impact resistance,good finishing response, weldability, formability, and machinability
|
0.50 – 0.75 Si Max 0.35 Fe 0.40 – 0.70 Mg |
T1 T5 |
25000 38000 |
15000 35000 |
16 10 |
|
6351 |
High strength structural alloy. Provides good fatigue and impact resistance
|
0.70 – 1.30 Si Max 0.50 Fe 0.40 – 0.80 Mg |
T1 T4 T5 T6 |
26000 32000 38000 42000 |
13000 19000 35000 37000 |
15 16 10 10 |
Si – Silicon
Fe – Iron
Mg – Magnesium
Cu – Copper
Generally, 6063 is the most common used extruded alloy, whereas 6061 or 6105 are used when higher strength required.
Temper
Temper is the combination of hardness and resilience in a piece of metal.
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T1
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Cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition. Usually associated with extruded products and limited to certain of the 6xxx series alloys. |
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T2
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Cooled from an elevated temperature shaping process, cold worked, and naturally aged to a substantially stable condition. Usually associated with cast products. |
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T3
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Solution heat-treated, cold worked, and naturally aged to a substantially stable condition. The working serves to increase the strength (T4 + cold work) |
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T4
|
Solution heat-treated and naturally aged to a substantially stable condition. |
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T5
|
Cooled from an elevated temperature shaping process and artificially aged. Usually associated with extruded products in certain of the 6xxx series alloys. (T1 + artificial age) |
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T6
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Solution heat-treated and artificially aged. A stable temper. (T4 + artificial age) |
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T7
|
Solution heat-treated and overaged/stabilized. Applies to alloy products which are thermally over-aged after solution heat-treatment to carry them beyond the point of maximum strength to provide control of some special characteristic. A stable temper. |
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T8
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Solution heat-treated, artificially aged, and cold worked. A stable temper. (T3 + artificial age) |
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T9
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Solution heat-treated, artificially aged, and cold worked. A stable temper. (T6 + cold work) |
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T10
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Cooled from an elevated temperature shaping process, cold worked, and artificially aged. Usually associated with cast products. A stable temper. (T2 + artificial age) |
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T-51
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Applies to extruded products when stress-relieved by stretching the indicated amount. Stretching is performed after solution heat treatment or after cooling from an elevated temperature shaping process. No straightening takes place after stretching. |
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T-510
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Applies to extruded products and to drawn tube when stress-relieved by stretching the indicated amount. Stretching is performed after solution heat treatment or after cooling from an elevated temperature shaping process. No straightening takes place after stretching. |
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T-511
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Applies to extruded products, and to drawn tube when stress-relieved by stretching the indicated amount. Stretching is performed after solution heat treatment or after cooling from an elevated temperature shaping process. These products may receive minor straightening after stretching to comply with standard tolerances. |
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T-52
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Applies to products stress-relieved by compressing. |
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T-54
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Applies to die forgings stress-relieved by restriking cold. |
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H1
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Strain-hardened only. Applies to products which are strain-hardened or cold worked to obtain the desired strength level without supplementary thermal treatments. The number following this designation indicates the degree of strain-hardening. |
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H2
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Strain-hardened and partially annealed. Applies to products strain-hardened or old worked more than the desired final amount and then reduced in strength to that desired level by partial annealing. The number following this designation indicates the degree of strain hardening remaining after the partial annealing operation. |
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H3
|
Strain hardened and stabilized. Applies to products in the magnesium-aluminum class which will age-soften at room temperature after strain hardening. These products are strain-hardened to the desired amount and then subjected to a low temperature thermal operation which results in a stable but slightly lower tensile strength and improved ductility. The number following this designation indicates the degree of strain-hardening remaining after the stabilization treatment. |
Structure Use of Aluminium
Heat-treatable Alloys
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Alloy
|
Chemical Composition of Alloys
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Condition
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Mechanical Characteristics of the Alloys
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Product
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Thickness
|
|
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Over mm |
Up to and including mm |
|||||
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6061
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T6
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Extrusion*
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–
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150
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||
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Drawn
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–
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6.0
|
||||
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Tube
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6.0
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10
|
||||
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6063
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T4
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Extrusions
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–
|
150
|
||
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Drawn tube
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–
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10
|
||||
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Forgings
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–
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150
|
||||
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T5
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Extrusions
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–
|
150
|
|||
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T6
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Extrusions
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–
|
150
|
|||
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Drawn tube
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–
|
10
|
||||
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Forgings
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–
|
150
|
||||
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6082
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T4
|
.
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Extrusions
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–
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150
|
|
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Sheet
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0.2
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3.0
|
||||
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Plate
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3.0
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25
|
||||
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Drawn tube
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– |
6.0 |
||||
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6.0
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10
|
|||||
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Forgings
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–
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150
|
||||
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T6
|
.
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Extrusions
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–
|
20
|
||
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20
|
150
|
|||||
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Sheet
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0.2
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3.0
|
||||
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Plate
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3.0
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25
|
||||
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Drawn tube
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– |
6.0 |
||||
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6.0
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10
|
|||||
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Forgings
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–
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150
|
||||
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7020
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T4
|
.
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Extrusions
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–
|
25
|
|
|
Sheet and plate
|
.
|
25
|
||||
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T6
|
.
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Extrusions
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–
|
25
|
||
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Sheet and plate
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.
|
25
|
||||
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LM25
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.
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TB7
|
.
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Sand cast
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–
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–
|
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Chill cast
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–
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–
|
||||
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TF
|
.
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Sand cast
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–
|
–
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||
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Chill cast
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–
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–
|
||||
* Extrusions refers to bars, extruded round tubes and sections
Non-heat-treatable Alloys
|
Alloy
|
Chemical Composition of Alloys
|
Condition
|
Mechanical Characteristics of the Alloys
|
Product
|
Thickness
|
|
|
Over mm |
Up to and including mm |
|||||
|
1200
|
H14
|
Sheet
|
0.2
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12.5
|
||
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3103
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H14
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Sheet
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0.2
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12.5
|
||
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H18
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Sheet
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0.2
|
3
|
|||
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3105
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H14
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Sheet
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0.2
|
3
|
||
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H16
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Sheet
|
0.2
|
3
|
|||
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H18
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Sheet
|
0.2
|
3
|
|||
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5083
|
O
|
Extrusion*
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–
|
150
|
||
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Sheet and plate
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0.2
|
80
|
||||
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Drawn tube
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–
|
10
|
||||
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F
|
.
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Extrusion
|
–
|
150
|
||
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Sheet and plate
|
3
|
25
|
||||
|
Forgings
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–
|
150
|
||||
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H22
|
.
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Sheet and plate
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0.2
|
6
|
||
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Drawn tube
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–
|
10
|
||||
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5154A
|
O
|
Extrusion
|
–
|
150
|
||
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Sheet and plate
|
0.2
|
6
|
||||
|
Drawn tube
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–
|
10
|
||||
|
F
|
.
|
Extrusion
|
–
|
150
|
||
|
Forgings
|
–
|
150
|
||||
|
H22
|
.
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Sheet and plate
|
0.2
|
6
|
||
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H24
|
.
|
Sheet and plate
|
0.2
|
6
|
||
|
Drawn tube
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–
|
10
|
||||
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5251
|
F
|
.
|
Seam welded tube
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0.8
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1.0
|
|
|
1.2
|
2.0
|
|||||
|
Forgings
|
–
|
150
|
||||
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H22
|
.
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Sheet and plate
|
0.2
|
6
|
||
|
H24
|
.
|
Sheet and plate
|
0.2
|
6
|
||
|
5454
|
O
|
Extrusion
|
–
|
150
|
||
|
Sheet and plate
|
0.2
|
6
|
||||
|
F
|
.
|
Extrusion
|
–
|
150
|
||
|
H22
|
.
|
Sheet
|
0.2
|
3
|
||
|
H24
|
.
|
Sheet
|
0.2
|
3
|
||
|
LM5
|
.
|
F
|
.
|
Sand cast
|
–
|
–
|
|
Chill cast
|
–
|
–
|
||||
|
LM6
|
.
|
F
|
.
|
Sand cast
|
–
|
–
|
|
Chill cast
|
–
|
–
|
||||
* Extrusions refers to bars, extruded round tubes and sections
Dimension
BS 1161 standard extruded sections- range of sizes:
| Section type | Size range (mm) |
| Equal angles | 30 x 30-120 x 120 |
| Unequal angles | 50 x 38-140 x 105 |
| Channels | 60 x 30-240 x 100 |
| T-sections | 50 x 38-120 x 90 |
| I-sections | 60 x 30-160 x 80 |
| Equal bulb angles | 50 x 50-120 x 120 |
| Unequal bulb angles | 50 x 37.5-140 x 105 |
| Lipped channels | 80 x 40-140 x 70 |
| Bulb T-sections | 90 x 75-180 x 150 |
For curtain wall and cladding framing member, the dimension of the aluminium extrusion would be modified and custom-made.
Workability
It can be riveted, bolted, welded, brazed and soldered.
Solubility of Other Metals
Silicon, copper, iron, zinc, tin, manganese dissolve readily in aluminium. Sodium and potassium are practically insoluble in it, and titanium, vanadium, boron, nickel, and chromium have low solubility. Hydrogen is the only gas soluble in aluminium to any extent.
Manufacturing Process
The term extrusion is usually applied to both the process, and the product obtained, when a hot cylindrical billet of aluminium is pushed through a shaped die (forward or direct extrusion, see Figure 1). The resulting section can be used in long lengths or cut into short parts for use in structures, vehicles or components.
Aluminium alloys are delivered in the form of long cylinders called logs. And logs are cut into billets by log shears, which are inserted into extrusion press.
Pre-cut billets can be also ordered. The advantage of the log shear in workshop is, billet can be cut in the size most fit to the press in order to maximize the run-out table utilization, and to reduce the wastage.In many of extrusion plants in Asia, especially in China, ingots, instead of logs and billets are ordered, and smelted and cast into logs and billets in house.
Finishes
Finishes of aluminium extrusion affect its durability against weathering condition.
Anodized
The durability of anodising is a direct result of it fusing into the surface of the aluminium forming a hard oxide coating. It comes in a wide range of colours and recently it comes with much tighter control for colour matching.
It is difficult to obtain regularity in colour. However, anodising is being increasingly specified by architect for its durability and because it allows the metallic quality of the aluminium to remain visible.
Anodizing is an electrolytic coating process, and the metal deposit and colour is dependent upon time and current passed.
Liquid organic coating (i.e. Fluorocarbon or PVDF or PVF2)
Polyester powder coating
When using polyester powder coating careful specification and monitoring is required to ensure that a thoroughly tested polymer is used and good adhesion achieved. The powder coating process consists of three main stages:
- Pre-treatment (involves the application of zinc phosphate conversion coatings)
- Spraying the powder
- Fusing the powder by heat treatment
It is possible to specify polyester powder coating, which includes anti-bacterial agents in the coating. This will kill common bacteria, such as Escherica coli, Salmonella and MSRA, which comes into contact with the coated component.
Mill finished (= unfinished)
This is not a sufficient protection for a corrosive or marine environment and has a relatively consistent grey appearance, which can be describe as sugary. Marine cast aluminium component is often specified as polished, which can be expensive finish and needs regular maintenance.
Density
The density of aluminium is approximately one-third that of steel and copper. The density of pure aluminium is 2.6898 g/cm3. Trace amounts of alloying elements produce cast and wrought alloys in the density range of 2.66-2.80 g/cm3.
Modulus Elasticity
Aluminium is found to be resistant to the attack of nitric acid, dissolves slowly in concentrated sulphuric acid and is soluble in hydrochloric acid. At normal temperature, it is not affected by sulphur, carbonic acid, carbonic oxide, vinegar, sea water, etc. But it is rapidly corroded by caustic alkalis.
Thermal Expansion
Pure aluminium has a coefficient of thermal expansion approximately twice that of steel at 23.5 x 10-6 /ºC in the range 10-100 ºC.
Alloying elements have a small effect on this value. Figures in the range 20-25 x 10-6 /ºC (for casting alloys) to 20-24 x 10-6 /ºC for wrought alloys.
Thermal Conductivity
Aluminium is a good conductor of heat with conductivity for pure aluminium of 244 W/m ºC (about 4.5 times that of steel).
The thermal conductivity reduces with the increased alloying to 109 W/m ºC for wrought alloys and to below 100 W/m ºC for some casting alloy.
Service Temperature Limit
Melting point: 658.7 ºC (but the melting point of some alloys can as low as 530ºC)
Boiling point: 2467 ºC
At temperature below zero, aluminium and aluminium alloys exhibit higher tensile strength and elongation than at room temperatures. No alloys suffer low temperature brittleness and there is no point below which brittle fracture occurs.
Aluminium and its alloys show considerable reduction of strength at temperature above 100ºC. At 200ºC the strength is approximately half of that at room temperature. By 350ºC, most alloys will have lost most of their strength. Strength is not restored as temperature falls as the effect of work hardening will have been removed.
Strength
The strength of aluminium depends on the composition and on the thermal and mechanical treatment to which it has been subjected.
Its strength can be increased by alloying and proper working to as high as 689.5 MN/m².
Specific Gravity
2.6989 at 20ºC.
Tensile Strength
48.265 MN/m2 for 99.996% pure aluminium
Corrosion Resistance
Aluminium combines readily with oxygen and is made corrosion resistance by the transparent film of aluminium oxide that quickly forms and is relatively inert to further chemical action.
Aluminium is readily attacked by alkalis and hydrochloric acid and slowly attacked by dilute acids. It is inert to sulphur. In direct contact with metals other than zinc, cadmium, magnesium, and on magnetic stainless steel, aluminium is subject to certain types of galvanic action and should therefore be electrically insulated from other metals.
Electrical Resistance and Conductivity
Pure aluminium has a high electrical conductivity at 63% of IACS and an electrical resistivity of 2.69 µ cm at 20ºC. These values increase with alloying to a resistance of over 6 µ cm at 20ºC for some alloys and conductivity down to below 28% IACS.
Fire Resistance
Where fire resistance is required, sufficient insulation must be provided to prevent the temperature of metal from rising above 200ºC.
Acid Resistance
Aluminium is found to be resistant to the attack of nitric acid, dissolves slowly in concentrated sulphuric acid and is soluble in hydrochloric acid. At normal temperature, it is not affected by sulphur, carbonic acid, carbonic oxide, vinegar, sea water, etc. But it is rapidly corroded by caustic alkalis.
Fatigue
Typical value of fatigue strength at 50 x 106 cycles range from 20MPa for annealed commercially pure aluminium to 124 MPa for 6082-TG material. Alloys with high manganese contents will exhibit higher values. Fatigue strength may be drastically reduced by unsatisfactory weld details.
Creep
Only commercially pure aluminium shows significant creep at room temperature. However, if the working temperature is held at around 200-250ºC, then the creep of some alloys will be significant.
Reflectivity
For pure aluminium with a clean bright surface 80%-85% of visible incident radiation and about 90% of heat will be reflected. Emissivity is typically 0.30 for a wavelength of 0.65 µmm.