Aluminum is the most abundant metal and the third most abundant chemical element in the earth's
crust, comprising over 8% of its weight. Only oxygen and silicon are more prevalent. Yet, until about
150 years ago aluminum in its metallic form was unknown to man. The reason for this is that
aluminum, unlike iron or copper, does not exist as a metal in nature. Because of its chemical activity
and its affinity for oxygen, aluminum is always found combined with other elements, mainly as
aluminum oxide. As such it is found in nearly all clays and many minerals. Rubies and sapphires
are aluminum oxide colored by trace impurities, and corundum, also aluminum oxide, is the second
hardest naturally occurring substance on earth—only a diamond is harder.
It was not until 1886 that scientists learned how to economically extract aluminum from aluminum
oxide via electrolytic reduction. Yet in the more than 100 years since that time, aluminum has become
the second most widely used of the approximately 60 naturally occurring metals, behind only iron.
One property of aluminum that everyone is familiar with is its light weight or, technically, its low
specific gravity. The specific gravity of aluminum is only 2.7 times that of water, and roughly one third that of steel or copper. An easy number to remember is that 1 in.3 of aluminum weighs 0.1 Ib;
1 ft3 weighs 170 Ib compared to 62 Ib for water and 490 Ib for steel. The following are some other
properties of aluminum and its alloys that will be examined in more detail in later sections:
Formability. Aluminum can be formed by every process in use today and in more ways than
any other metal. Its relatively low melting point, 122O0F, while restricting high-temperature
applications to about 500-60O0F, does make it easy to cast, and there are over 1000 foundries
casting aluminum in this country.
Mechanical Properties. Through alloying, naturally soft aluminum can attain strengths twice
that of mild steel.
Strength-to-Weight Ratio. Some aluminum alloys are among the highest strength to weight
materials in use today, in a class with titanium and superalloy steels. This is why aluminum
alloys are the principal structural metal for commercial and military aircraft.
Cryogenic Properties. Unlike most steels, which tend to become brittle at cryogenic temperatures,
aluminum alloys actually get tougher at low temperatures and hence enjoy many cryogenic
applications.
Corrosion Resistance. Aluminum possesses excellent resistance to corrosion by natural atmospheres
and by many foods and chemicals.
High Electrical and Thermal Conductivity. On a volume basis the electrical conductivity of
pure aluminum is roughly 60% of the International Annealed Copper Standard, but pound for
pound aluminum is a better conductor of heat and electricity than copper and is surpassed
only by sodium, which is a difficult metal to use in everyday situations.
Reflectivity. Aluminum can accept surface treatment to become an excellent reflector and it
does not dull from normal oxidation.
Finishability. Aluminum can be finished in more ways than any other metal used today
electrical conductors, chemical equipment, and sheet metal work, it is a relatively weak material, and
its use is restricted to applications where strength is not an important factor. Some strengthening of
the pure metal can be achieved through cold working, called strain hardening. However, much greater
strengthening is obtained through alloying with other metals, and the alloys themselves can be further
strengthened through strain hardening or heat treating. Other properties, such as castability and machinability,
are also improved by alloying. Thus, aluminum alloys are much more widely used than is
the pure metal, and in many cases, when aluminum is mentioned, the reference is actually to one of
the many commercial alloys of aluminum.
The principal alloying additions to aluminum are copper, manganese, silicon, magnesium, and
zinc; other elements are also added in smaller amounts for metallurgical purposes. Since there have
been literally hundreds of aluminum alloys developed for commercial use, the Aluminum Association
formulated and administers special alloy designation systems to distinguish and classify the alloys
in a meaningful manner
The wrought category is a broad one, since aluminum alloys may be shaped by virtually every known
process, including rolling, extruding, drawing, forging, and a number of other, more specialized
processes. Cast alloys are those that are poured molten into sand (sand casting) or high-strength steel
(permanent mold or die casting) molds, and are allowed to solidify to produce the desired shape.
The wrought and cast alloys are quite different in composition; wrought alloys must be ductile for
fabrication, while cast alloys must be fluid for castability.
In 1974, the Association published a designation system for wrought aluminum alloys that classifies
the alloys by major alloying additions. This system is now recognized worldwide under the
International Accord for Aluminum Alloy Designations, administered by the Aluminum Association,
and is published as American Standards Institute (ANSI) Standard H35.1. More recently, a similar
system for casting alloys was introduced.
Each wrought or cast aluminum alloy is designated by a number to distinguish it as a wrought
or cast alloy and to categorize the alloy. A wrought alloy is given a four-digit number. The first digit
classifies the alloy by alloy series, or principal alloying element. The second digit, if different than
O, denotes a modification in the basic alloy. The third and fourth digits form an arbitrary number
Designation System for
Wrought Aluminum Alloys
Alloy Series Description or Major Alloying Element
Ixxx 99.00% minimum aluminum
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesium and silicon
7xxx Zinc
8xxx Other element
9xxx Unused series
which identifies the specific alloy in the series.* A cast alloy is assigned a three-digit number followed
by a decimal. Here again the first digit signifies the alloy series or principal addition; the second and
third digits identify the specific alloy; the decimal indicates whether the alloy composition is for the
final casting (0.0) or for ingot (0.1 or 0.2). A capital letter prefix (A, B, C, etc.) indicates a modification
of the basic alloy.
The designation systems for wrought and cast aluminum alloys are shown in Tables
Specification of an aluminum alloy is not complete without designating the metallurgical condition,
or temper, of the alloy. A temper designation system, unique for aluminum alloys, was developed
by the Aluminum Association and is used for all wrought and cast alloys. The temper designation
follows the alloy designation, the two being separated by a hyphen. Basic temper designations consist
of letters; subdivisions, where required, are indicated by one or more digits following the letter. The
basic tempers are:
F—As-Fabricated. Applies to the products of shaping processes in which no special control
over thermal conditions or strain hardening is employed. For wrought products, there are no
mechanical property limits.
O—Annealed. Applies to wrought products that are annealed to obtain the lowest strength
temper, and to cast products that are annealed to improve ductility and dimensional stability.
The O may be followed by a digit other than zero.
Alloy Description or Major Alloying Element
Series
Ixx.x 99.00% minimum aluminum
2xx.x Copper
3xx.x Silicon plus copper and /or magnesium
4xx.x Silicon
5xx.x Magnesium
6xx.x Unused series
7xx.x Zinc
Sxx.x
9xx.x Tin
Other element
H—Strain-Hardened (Wrought Products Only). Applies to products that have their strength
increased by strain hardening, with or without supplementary thermal treatments to produce
some reduction in strength. The H is always followed by two or more digits. (See Table 3.3.)
W—Solution Heat Treated. An unstable temper applicable only to alloys that spontaneously
age at room temperature after solution heat treatment. This designation is specific only when
the period of natural aging is indicated; for example: W l/2 hr.
T—Thermally Treated to Produce Stable Tempers Other than F, O, or H. Applies to products
that are thermally treated, with or without supplementary strain hardening, to produce stable
tempers. The T is always followed by one or more digits.
Nonheat-treatable alloys are those that derive their strength from the hardening effect of
elements such as manganese, iron, silicon, and magnesium, and are further strengthened by strain
hardening. They include the Ixxx, 3xxx, 4xxx, and 5xxx series alloys. Heat-treatable alloys a
First digit indicates specific sequence of treatments:
Tl—Cooled from an elevated-temperature shaping process and naturally aged to a substantially
stable condition
T2—Cooled from an elevated-temperature shaping process, cold worked, and naturally aged to a
substantially stable condition
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 artifically aged
T6—Solution heat-treated and then artifically aged
T7—Solution heat-treated and overaged/stabilized
T8—Solution heat-treated, cold worked, and then artificially aged
T9—Solution heat-treated, artificially aged, and then cold worked
TlO—Cooled from an elevated-temperature shaping process, cold worked, and then artificially
aged
Second digit indicates variation in basic treatment:
Examples:
T42 or T62—Heat treated to temper by user
Additional digits indicate stress relief:
Examples:
TX51 or TXX51—Stress relieved by stretching
TX52 or TXX52—Stress relieved by compressing
TX54 or TXX54—Stress relieved by combination of stretching and compressing strengthened by a combination of solution heat treatment and natural or controlled aging for precipitation
hardening, and include the 2xxx, some 4xxx, 6xxx, and 7xxx series alloys. Castings are not
normally strain hardened, but many are solution heat-treated and aged for added strength.
In Table 3.5 typical mechanical properties are shown for several representative nonheat-treatable
alloys in the annealed, half-hard and full-hard tempers; values for super purity aluminum (99.99%)
are included for comparison. Typical properties are usually higher than minimum, or guaranteed,
properties and are not meant for design purposes but are useful for comparisons. It should be noted
that pure aluminum can be substantially strain hardened, but a mere 1% alloying addition produces
a comparable tensile strength to that of fully hardened pure aluminum with much greater ductility
in the alloy. And the alloys can then be strain hardened to produce even greater strengths. Thus, the
alloying effect is compounded. Note also that, while strain hardening increases both tensile and yield
strengths, the effect is more pronounced for the yield strength so that it approaches the tensile strength
in the fully hardened temper. Ductility and workability are reduced as the material is strain hardened,
and most alloys have limited formability in the fully hardened tempers.
Table 3.6 lists typical mechanical properties and nominal compositions of some representative
heat-treatable aluminum alloys. One can readily see that the strengthening effect of the alloying
ingredients in these alloys is not reflected in the annealed condition to the same extent as in the
nonheat-treatable alloys, but the true value of the additions can be seen in the aged condition. Presently,
heat-treatable alloys are available with tensile strengths approaching 100,000 psi.
Again, casting alloys cannot be work hardened and are either used in as-cast or heat-treated
conditions. Typical mechanical properties for commonly used casting alloys range from 20 to 50 ksi
for ultimate tensile strength, from 15 to 50 ksi tensile yield strength and up to 20% elongation. The
range of strengths available with wrought aluminum alloys is shown graphically
buildings to tanks and piping for handling cryogenic liquids, and even bridges and major buildings
and roof structures. In establishing appropriate working stresses the factors of safety applied to the
ultimate strength and yield strength of the aluminum alloy vary with the specific application. For
building and similar type structures a factor of safety of 1.95 is applied to the tensile ultimate strength
Typical Mechanical Properties of Representative Nonheat-Treatable Aluminum
Alloy Nominal Composition Temper Tensile stenght ( ksi) yiled Strength ( ksi) Elegotion(% in 2 in) Hardness (BHN)
1199 99.9+% Al O 6.5 1.5 50 —
H 18 17 16 5 —
1100 99+% Al O 13 5 35 23
H14 18 17 9 32
HIS 24 22 5 44
3003 1.2% Mn O 16 6 30 28
H14 22 21 8 40
HIS 29 27 4 55
3004 1.2% Mn O 26 10 20 43
1.0% Mg H34 35 29 9 63
H38 41 36 5 77
5005 0.8% Mg O 13 6 25 28
H14 23 22 6 41
HIS 29 28 4 51
5052 2.5% Mg O 28 13 25 47
H34 38 31 10 68
H38 42 37 7 77
5456 5.1% Mg O 45 23 24 70
0.8% Mn H321, H116 51 37 16 90
B443.0 5.0% Si F* 19 8 8 40
F* 23 9 10 45
514.0 4.0% Mg P 25 12 9 50
...........................
crust, comprising over 8% of its weight. Only oxygen and silicon are more prevalent. Yet, until about
150 years ago aluminum in its metallic form was unknown to man. The reason for this is that
aluminum, unlike iron or copper, does not exist as a metal in nature. Because of its chemical activity
and its affinity for oxygen, aluminum is always found combined with other elements, mainly as
aluminum oxide. As such it is found in nearly all clays and many minerals. Rubies and sapphires
are aluminum oxide colored by trace impurities, and corundum, also aluminum oxide, is the second
hardest naturally occurring substance on earth—only a diamond is harder.
It was not until 1886 that scientists learned how to economically extract aluminum from aluminum
oxide via electrolytic reduction. Yet in the more than 100 years since that time, aluminum has become
the second most widely used of the approximately 60 naturally occurring metals, behind only iron.
PROPERTIES OF ALUMINUM
Let us consider the properties of aluminum that lead to its wide use.One property of aluminum that everyone is familiar with is its light weight or, technically, its low
specific gravity. The specific gravity of aluminum is only 2.7 times that of water, and roughly one third that of steel or copper. An easy number to remember is that 1 in.3 of aluminum weighs 0.1 Ib;
1 ft3 weighs 170 Ib compared to 62 Ib for water and 490 Ib for steel. The following are some other
properties of aluminum and its alloys that will be examined in more detail in later sections:
Formability. Aluminum can be formed by every process in use today and in more ways than
any other metal. Its relatively low melting point, 122O0F, while restricting high-temperature
applications to about 500-60O0F, does make it easy to cast, and there are over 1000 foundries
casting aluminum in this country.
Mechanical Properties. Through alloying, naturally soft aluminum can attain strengths twice
that of mild steel.
Strength-to-Weight Ratio. Some aluminum alloys are among the highest strength to weight
materials in use today, in a class with titanium and superalloy steels. This is why aluminum
alloys are the principal structural metal for commercial and military aircraft.
Cryogenic Properties. Unlike most steels, which tend to become brittle at cryogenic temperatures,
aluminum alloys actually get tougher at low temperatures and hence enjoy many cryogenic
applications.
Corrosion Resistance. Aluminum possesses excellent resistance to corrosion by natural atmospheres
and by many foods and chemicals.
High Electrical and Thermal Conductivity. On a volume basis the electrical conductivity of
pure aluminum is roughly 60% of the International Annealed Copper Standard, but pound for
pound aluminum is a better conductor of heat and electricity than copper and is surpassed
only by sodium, which is a difficult metal to use in everyday situations.
Reflectivity. Aluminum can accept surface treatment to become an excellent reflector and it
does not dull from normal oxidation.
Finishability. Aluminum can be finished in more ways than any other metal used today
ALUMINUMALLOYS
While commercially pure aluminum (defined as at least 99% aluminum) does find application inelectrical conductors, chemical equipment, and sheet metal work, it is a relatively weak material, and
its use is restricted to applications where strength is not an important factor. Some strengthening of
the pure metal can be achieved through cold working, called strain hardening. However, much greater
strengthening is obtained through alloying with other metals, and the alloys themselves can be further
strengthened through strain hardening or heat treating. Other properties, such as castability and machinability,
are also improved by alloying. Thus, aluminum alloys are much more widely used than is
the pure metal, and in many cases, when aluminum is mentioned, the reference is actually to one of
the many commercial alloys of aluminum.
The principal alloying additions to aluminum are copper, manganese, silicon, magnesium, and
zinc; other elements are also added in smaller amounts for metallurgical purposes. Since there have
been literally hundreds of aluminum alloys developed for commercial use, the Aluminum Association
formulated and administers special alloy designation systems to distinguish and classify the alloys
in a meaningful manner
ALLOY DESIGNATION SYSTEMS
Aluminum alloys are divided into two classes according to how they are produced: wrought and cast.The wrought category is a broad one, since aluminum alloys may be shaped by virtually every known
process, including rolling, extruding, drawing, forging, and a number of other, more specialized
processes. Cast alloys are those that are poured molten into sand (sand casting) or high-strength steel
(permanent mold or die casting) molds, and are allowed to solidify to produce the desired shape.
The wrought and cast alloys are quite different in composition; wrought alloys must be ductile for
fabrication, while cast alloys must be fluid for castability.
In 1974, the Association published a designation system for wrought aluminum alloys that classifies
the alloys by major alloying additions. This system is now recognized worldwide under the
International Accord for Aluminum Alloy Designations, administered by the Aluminum Association,
and is published as American Standards Institute (ANSI) Standard H35.1. More recently, a similar
system for casting alloys was introduced.
Each wrought or cast aluminum alloy is designated by a number to distinguish it as a wrought
or cast alloy and to categorize the alloy. A wrought alloy is given a four-digit number. The first digit
classifies the alloy by alloy series, or principal alloying element. The second digit, if different than
O, denotes a modification in the basic alloy. The third and fourth digits form an arbitrary number
Designation System for
Wrought Aluminum Alloys
Alloy Series Description or Major Alloying Element
Ixxx 99.00% minimum aluminum
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesium and silicon
7xxx Zinc
8xxx Other element
9xxx Unused series
which identifies the specific alloy in the series.* A cast alloy is assigned a three-digit number followed
by a decimal. Here again the first digit signifies the alloy series or principal addition; the second and
third digits identify the specific alloy; the decimal indicates whether the alloy composition is for the
final casting (0.0) or for ingot (0.1 or 0.2). A capital letter prefix (A, B, C, etc.) indicates a modification
of the basic alloy.
The designation systems for wrought and cast aluminum alloys are shown in Tables
Specification of an aluminum alloy is not complete without designating the metallurgical condition,
or temper, of the alloy. A temper designation system, unique for aluminum alloys, was developed
by the Aluminum Association and is used for all wrought and cast alloys. The temper designation
follows the alloy designation, the two being separated by a hyphen. Basic temper designations consist
of letters; subdivisions, where required, are indicated by one or more digits following the letter. The
basic tempers are:
F—As-Fabricated. Applies to the products of shaping processes in which no special control
over thermal conditions or strain hardening is employed. For wrought products, there are no
mechanical property limits.
O—Annealed. Applies to wrought products that are annealed to obtain the lowest strength
temper, and to cast products that are annealed to improve ductility and dimensional stability.
The O may be followed by a digit other than zero.
Alloy Description or Major Alloying Element
Series
Ixx.x 99.00% minimum aluminum
2xx.x Copper
3xx.x Silicon plus copper and /or magnesium
4xx.x Silicon
5xx.x Magnesium
6xx.x Unused series
7xx.x Zinc
Sxx.x
9xx.x Tin
Other element
H—Strain-Hardened (Wrought Products Only). Applies to products that have their strength
increased by strain hardening, with or without supplementary thermal treatments to produce
some reduction in strength. The H is always followed by two or more digits. (See Table 3.3.)
W—Solution Heat Treated. An unstable temper applicable only to alloys that spontaneously
age at room temperature after solution heat treatment. This designation is specific only when
the period of natural aging is indicated; for example: W l/2 hr.
T—Thermally Treated to Produce Stable Tempers Other than F, O, or H. Applies to products
that are thermally treated, with or without supplementary strain hardening, to produce stable
tempers. The T is always followed by one or more digits.
MECHANICAL PROPERTIES OF ALUMINUM ALLOYS
Wrought aluminum alloys are generally thought of in two categories: nonheat-treatable and heattreatable.Nonheat-treatable alloys are those that derive their strength from the hardening effect of
elements such as manganese, iron, silicon, and magnesium, and are further strengthened by strain
hardening. They include the Ixxx, 3xxx, 4xxx, and 5xxx series alloys. Heat-treatable alloys a
First digit indicates specific sequence of treatments:
Tl—Cooled from an elevated-temperature shaping process and naturally aged to a substantially
stable condition
T2—Cooled from an elevated-temperature shaping process, cold worked, and naturally aged to a
substantially stable condition
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 artifically aged
T6—Solution heat-treated and then artifically aged
T7—Solution heat-treated and overaged/stabilized
T8—Solution heat-treated, cold worked, and then artificially aged
T9—Solution heat-treated, artificially aged, and then cold worked
TlO—Cooled from an elevated-temperature shaping process, cold worked, and then artificially
aged
Second digit indicates variation in basic treatment:
Examples:
T42 or T62—Heat treated to temper by user
Additional digits indicate stress relief:
Examples:
TX51 or TXX51—Stress relieved by stretching
TX52 or TXX52—Stress relieved by compressing
TX54 or TXX54—Stress relieved by combination of stretching and compressing strengthened by a combination of solution heat treatment and natural or controlled aging for precipitation
hardening, and include the 2xxx, some 4xxx, 6xxx, and 7xxx series alloys. Castings are not
normally strain hardened, but many are solution heat-treated and aged for added strength.
In Table 3.5 typical mechanical properties are shown for several representative nonheat-treatable
alloys in the annealed, half-hard and full-hard tempers; values for super purity aluminum (99.99%)
are included for comparison. Typical properties are usually higher than minimum, or guaranteed,
properties and are not meant for design purposes but are useful for comparisons. It should be noted
that pure aluminum can be substantially strain hardened, but a mere 1% alloying addition produces
a comparable tensile strength to that of fully hardened pure aluminum with much greater ductility
in the alloy. And the alloys can then be strain hardened to produce even greater strengths. Thus, the
alloying effect is compounded. Note also that, while strain hardening increases both tensile and yield
strengths, the effect is more pronounced for the yield strength so that it approaches the tensile strength
in the fully hardened temper. Ductility and workability are reduced as the material is strain hardened,
and most alloys have limited formability in the fully hardened tempers.
Table 3.6 lists typical mechanical properties and nominal compositions of some representative
heat-treatable aluminum alloys. One can readily see that the strengthening effect of the alloying
ingredients in these alloys is not reflected in the annealed condition to the same extent as in the
nonheat-treatable alloys, but the true value of the additions can be seen in the aged condition. Presently,
heat-treatable alloys are available with tensile strengths approaching 100,000 psi.
Again, casting alloys cannot be work hardened and are either used in as-cast or heat-treated
conditions. Typical mechanical properties for commonly used casting alloys range from 20 to 50 ksi
for ultimate tensile strength, from 15 to 50 ksi tensile yield strength and up to 20% elongation. The
range of strengths available with wrought aluminum alloys is shown graphically
WORKINGSTRESSES
Aluminum is used in a wide variety of structural applications. These range from curtain walls onbuildings to tanks and piping for handling cryogenic liquids, and even bridges and major buildings
and roof structures. In establishing appropriate working stresses the factors of safety applied to the
ultimate strength and yield strength of the aluminum alloy vary with the specific application. For
building and similar type structures a factor of safety of 1.95 is applied to the tensile ultimate strength
Typical Mechanical Properties of Representative Nonheat-Treatable Aluminum
Alloys (Not for Design Purposes)Tensile Yield Nominal Strength Strength Elongation Hardness
Alloy Nominal Composition Temper Tensile stenght ( ksi) yiled Strength ( ksi) Elegotion(% in 2 in) Hardness (BHN)1199 99.9+% Al O 6.5 1.5 50 —
H 18 17 16 5 —
1100 99+% Al O 13 5 35 23
H14 18 17 9 32
HIS 24 22 5 44
3003 1.2% Mn O 16 6 30 28
H14 22 21 8 40
HIS 29 27 4 55
3004 1.2% Mn O 26 10 20 43
1.0% Mg H34 35 29 9 63
H38 41 36 5 77
5005 0.8% Mg O 13 6 25 28
H14 23 22 6 41
HIS 29 28 4 51
5052 2.5% Mg O 28 13 25 47
H34 38 31 10 68
H38 42 37 7 77
5456 5.1% Mg O 45 23 24 70
0.8% Mn H321, H116 51 37 16 90
B443.0 5.0% Si F* 19 8 8 40
F* 23 9 10 45
514.0 4.0% Mg P 25 12 9 50
...........................
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