A01 481
A01 481
A01 481
Aluminum Alloys
J. Paul Lyle, Aluminum Company of America, Alcoa Center, Pennsylvania 15069, United States
Douglas A. Granger, Aluminum Company of America, Alcoa Center, Pennsylvania 15069, United States
Robert E. Sanders, Aluminum Company of America, Alcoa Technical Center, Pittsburgh, Pennsylvania
15219-1859, United States
properties and physical metallurgy are given in the characteristics of the alloys. Of the elements
[4], [5]. Commercial aluminum alloy products commonly added, copper, magnesium, silicon,
are described in [6], [8]. Commercial alloys of and zinc have high diffusion coefficients; other
other metals that contain aluminum are given elements diffuse only slowly [1, p. 118].
in [7], [8, pp. 237 ff.], [9]. Heat treatment [10],
surface treatment [11], and joining [12] of alu- Table 1. Elements in commercial aluminum alloys: maximum spec-
ified, wt %
minum alloys have been described.
Element Wrought alloys Casting alloys
Ag – 1.0
Be – 0.3
2. Metallurgy of Aluminum Alloys Bi 0.7 –
Co 1.9 0.3
The properties of aluminum alloys depend on the Cr 0.40 0.6
Cu 6.8 11.0
metallurgical structure, which in turn depends on Fe 2.0 2.0
composition, solidification processes, and post- Mg 5.6 10.6
Mn 1.8 0.8
solidification thermal and deformation process- Ni 2.3 3.0
ing [1], [4], [5]. O 0.5 –
Pb 0.7 0.25
Sb – 0.3
Si 13.5 23.0
2.1. Composition Sn
Ti
22.0
0.2
7.0
0.35
V 0.15 0.2
Many alloying elements are added to aluminum Zn 8.7 8.0
Zr 0.3 0.3
to enhance its properties (Table 1) [13], [14]. The
major elements increasing strength are copper
(see Fig. 21), magnesium (Fig. 1), manganese Commercial alloys are usually multicompo-
(Fig. 2), silicon (Fig. 3), and zinc (Fig. 4). All nent systems, and the phase diagrams are fre-
these have maximum solid solubility limits in quently complex. One important precipitation-
excess of 1.5 % (Table 2) [1, pp. 362 – 3]. El- hardening system, Al – Mg – Si, is shown in Fig-
ements with lower solubilities, e.g., chromium ure 6 (page after next) in the form of contour
(Fig. 5), zirconium, and titanium, are added to maps representing the solvus, solidus, and liq-
certain alloys to aid in controlling aspects of met- uidus surfaces.
allurgical structure, e.g., as-cast grain size and
the nature of recrystallization, and thus to affect
Cr Cu Fe Mg Mn Si Zn ∗ Zr Quasi- Quasi-
Mg2 Si MgZn2
Eutectic or peritectic 661 ∗∗ 548 655 450 659 577 382 661 ∗∗ 595 475
temperature, ◦ C
Solubility at eutectic 0.77 ∗∗ 5.65 0.052 14.9 1.82 1.65 82.3 0.28 ∗∗ 1.85 16.9
temperature, wt %
Solubility, wt % at
650 ◦ C 0.71 0.50 0.049 0.6 1.67 0.12 2.4 0.25 0.19
600 ◦ C 0.47 2.97 0.025 3.6 1.03 1.00 14.6 0.15 1.37
550 ◦ C 0.27 5.55 0.013 7.0 0.65 1.30 27.4 0.08 1.47
500 ◦ C 0.15 4.05 0.006 10.6 0.35 0.80 40.7 0.05 1.08
450 ◦ C 0.10 2.55 14.9 0.48 64.4 0.78 14.8
400 ◦ C 0.07 1.50 11.5 0.29 81.3 0.52 10.7
350 ◦ C 0.85 8.7 0.17 81.5 7.2
300 ◦ C 0.45 6.3 0.10 79.0 4.5
250 ◦ C 0.20 4.5 0.07 22.4 2.64
200 ◦ C 2.9 0.05 12.4 1.34
Macrosegregation arises because of the flow ings contain some gas above the solid-state equi-
of segregated liquid from one area of a solidify- librium level, and all shrinkage porosity contains
ing casting to another. A typical solute distribu- some gas.
tion across a 600-mm-thick commercial direct Hydrogen is the only gas that is significantly
chill ingot of 2024 alloy is illustrated in Fig- soluble in aluminum. At the melting point of alu-
ure 11. The driving forces for macrosegregation minum, hydrogen is 20 times more soluble in
are (1) shrinkage contraction that accompanies the liquid than in the solid (Fig. 12) [17]. Even
the transformation of liquid to solid, (2) density when the hydrogen level is reduced below the
differences in the liquid phase, and (3) convec- equilibrium concentration in molten aluminum
tive stirring that arises from the temperature gra- by fluxing, the low solubility of the gas in the
dient across the crater of a solidifying ingot. solid causes hydrogen to go into the remaining
liquid. When the internal gas pressure exceeds
atmospheric pressure, a bubble of gas can form.
For a given gas content, the amount of porosity
is increased by increased alloy freezing range
and decreased cooling rate (Fig. 13) [18].
2.3.1. Preheating
Figure 13. Relationship between porosity and hydrogen
content in semicontinuously direct chill (D.C.) cast ingot Ingot to be fabricated to wrought products is
a) Thick ingot; b) Thin ingot; c) 99.2 % Al; d) 99.99 % Al
Both thick (a) and thin (b) ingots are long freezing range usually preheated or homogenized [4, Chap. 5].
alloy 7xxx. This treatment, often near the melting temper-
ature, lasts a few hours to a few days. Preheat-
This porosity is not readily discernible in the ing alleviates microsegregation (coring and sol-
cast structure, but the pores expand considerably uble grain boundary segregation) by diffusion
on heating. The terms primary and secondary and makes the ingot more amenable to hot defor-
porosity are used to distinguish macroscopic and mation. Preheating followed by slow cooling is
microscopic forms of hydrogen porosity [19]. used to bring certain elements, e.g., manganese,
into solid solution and then precipitate them into
a more desirable form, usually very fine disper-
2.2.4. Nonmetallic Inclusions soids, for control of recrystallization, formabil-
ity, toughness, finishing, etc. During homoge-
There are three major types of solid inclusions nization, secondary porosity increases in size,
in aluminum alloys: (1) oxides, (2) borides, and but the porosity will eventually disappear, col-
(3) carbides. lapsing under the force of surface tension, if the
Molten aluminum reacts readily with mois- conditions in the furnace are favorable for the
ture in the atmosphere. The resulting aluminum loss of hydrogen from the ingot.
oxide film is generally quite coherent and in- During solidification, insoluble inter-
hibits further growth. But whenever the molten metallics, such as FeAl3 , precipitate with an
metal surface is disturbed, e.g., during the mix- angular geometry. During homogenizing heat
ing in of alloying elements or tapping from the treatments this type of precipitate becomes less
furnace to a transfer trough, a fresh oxide layer angular, and the fabricability of the ingot is
is formed immediately on the newly exposed enhanced.
surface. Therefore, oxides found in cast struc- There is sufficient residual stress in a direct
tures are usually filmlike. An exception is spinel, chill cast ingot to cause recrystallization and
MgAl2 O4 , which grows on Al – Mg alloy melts grain growth in alloys containing no insoluble
when the first-formed MgO film crystallizes and particles, as shown in Figure 14.
“breakaway” oxidation ensues. Spinel is partic-
ulate.
Borides originate from the presence of the
transition elements Zr, V, and Ti along with
boron in the Hall – Héroult cell. These impuri-
ties, which come from the alumina feed and an-
8 Aluminum Alloys
alloy (6061) also hardens rapidly for the first solid solution, artificial aging proceeds at mod-
100 h, but strength continues to rise more rapidly erately elevated temperatures as shown, with
than for the Al – Cu – Mg alloy for at least ten initially rising and then falling hardness. The
years. The strength of the Al – Zn – Mg – Cu al- changes in hardness are associated with the ap-
loy (7075) rises even more rapidly than that of pearance of G – P (Guinier – Preston) zones and
the Al – Mg – Si alloy, with no sign of leveling. their transformation to θ and θ.
Ductilities, as indicated by elongation tests, fall Artificial aging accelerates the precipitation
slowly as strengths rise. sequence; higher strengths are obtained within
The classic system for studying precipita- practical time frames. (Compare the curves in
tion hardening and artificial aging is Al – Cu. Figure 23 with the curve for 2024 in Figure 20.)
The equilibrium phase diagram (Fig. 21) shows The decrease in strength from overaging is as-
the maximum solid solubility of 5.65 wt % at sociated with changes in metallurgical structure,
548 ◦ C and a solubility of less than 0.2 % at resulting in more stable properties and dimen-
250 ◦ C. The aging sequence of an Al – 4 Cu al- sions and increased toughness and resistance to
loy is illustrated in Figure 22 [23]. (Al – 4 Cu is corrosion, in particular to exfoliation and stress-
an alloy consisting of 4 wt % Cu and the rest corrosion cracking in the Al – Zn – Mg – Cu al-
aluminum.) After solution heat treating above loys. These effects are illustrated in Figures 24
500 ◦ C and quenching to retain a supersaturated and 25 [24].
Fe 0.06 – 0.35
Si 0.05 – 0.15
H ca. 3×10−5 ∗
Na 0.002 – 0.004
Ca 0.002 – 0.004
Li 0.002 – 0.004
Ti, Zr 0.005 – 0.020
V, Cr 0.005 – 0.020
Al2 O3 variable
Al2 MgO4 (spinel) variable
Al4 C3 variable
TiB2 , etc. variable
combine gas removal with filtration. A num- 3.2. Casting Processes for Ingot
ber of these systems are described in [26]. Fig-
ure 30 illustrates a typical bed filtration system Direct chill (D.C.) casting is the primary method
(Alcoa 528) combined with a gas purge for hy- of ingot production in the aluminum industry
drogen and alkali metal reduction (Alcoa 622). [28]. Large ingots with either a rectangular or
Figure 31 shows a successful method of filtration circular cross section are cast for fabrication by
with a porous ceramic plate [27]. rolling to sheet or extruding to shaped profiles.
Some circular cross section ingot is used as forg-
ing stock and starting material for rod and wire
production. Figure 32 is a schematic illustrat-
ing the D.C. casting process developed around
1940, and Figure 33 shows a later modification
in which level transfer is used to avoid turbu-
lence with the associated oxide generation and
hydrogen pickup. The level-pour method pro-
duces high-quality ingot for forged products of
highest internal integrity. Direct chill ingot is
Figure 30. Molten metal fluxing and filtering system with usually cast in multiples, and the drop is termi-
Alcoa 622 and 528 metal treatment units nated when the ingot length reaches the depth of
the casting pit. A continuous casting process, in
which the ingot is cast horizontally, as depicted
in Figure 34, is widely used to produce a limited
number of alloys when large amounts of ingot
of one size are required.
Figure 38. Effect of sodium modification on microstructure of sand-cast A357.0 alloy as polished (120x)
A) Not modified; B) Modified
By far the most common casting alloys are 3.3.1. Die Casting
the hypoeutectic Al – Si type (Si in the range
4 – 12 %). Die castings freeze more rapidly than In the pressure die casting process the molten
permanent mold castings, which freeze more metal is injected at high velocity into a reusable
rapidly than sand castings. In order to maximize metal mold. The combination of the thin sections
the mechanical properties in permanent mold and high pressure insures a rapid freezing rate
and sand castings, modifiers are added to the (Fig. 8), but the accompanying contamination by
hypoeutectic Al – Si alloys. The most common gas entrapped as the metal enters the mold de-
modifiers are Na and Sr, small additions (0.005 – tracts from the potential advantages of the fine
0.1 %) having the effect of refining the usu- metallurgical structure. In addition, gas contam-
ally platelike silicon in the eutectic and giving it ination prevents heat treatment to develop pre-
a rodlike form. These structural changes, illus- cipitation strengthening. However, the true po-
trated in Figure 38 A and B, help to increase both tential of die casting will be realized only by
strength and ductility of the alloys. Antimony adopting techniques such as evacuating the mold
(0.05 – 0.1 %) may also be used to refine the before injecting the molten metal to minimize
eutectic structure; however, it does not modify gas pickup.
the alloy and the benefits are fully achieved only Because the die is made of steel, with no give,
after heat treatment. The hypereutectic Al – Si al- the alloys used must be resistant to hot cracking
loys, used primarily in die casting, are modified and reasonably fluid to fill the thin sections typ-
with phosphorus, because aluminum phosphide ical of die castings. In general, the alloys con-
is a potent nucleus for silicon. tain at least 0.6 % Fe, to reduce “soldering,” i.e.,
sticking of the cast part to the die as it is being
ejected.
Aluminum Alloys 17
3.3.2. Permanent Mold Casting and 6.30 mm, and foil is less than 0.15 mm thick.
Flat rolled products are produced in rolling mills
Like die casting, permanent mold casting (also by passing the metal between two cylindrical
called gravity die casting) employs a reusable rolls where it is subjected to high compressive
metal mold. Because the mold is gravity fed, forces to decrease thickness and increase length.
the pouring rate is relatively slow, but the metal When flat rolled products are made from ingot,
mold produces rapid freezing. Generally, per- initial passes are always at elevated tempera-
manent mold castings are larger, with thicker tures, but final passes may be hot or cold, de-
sections, than die castings. They have good me- pending on desired thickness and temper. When
chanical properties and are usually sound, pro- continuously cast strip is the starting material,
vided the alloys exhibit good fluidity and resist- initial passes may be either hot or cold. Inter-
ance to hot cracking. Mechanical properties can mediate heating may be used to promote homo-
be improved further by heat treatment. geneity and to remove prior strain. After the final
rolling pass, heat-treatable alloys are annealed or
solution heat treated and aged to produce the de-
3.3.3. Sand Casting sired temper: some alloy-tempers require strain
after quenching or aging. Nonheat-treatable al-
Sand casting is the least expensive process, but loys are annealed, partially annealed, or stabi-
the mold, which is formed by ramming sand lized to produce the desired temper.
mixed with bonding agent around a pattern, is The size of ingot used for making flat rolled
not reusable. Like permanent mold casting, the products varies widely in thickness, width, and
sand mold is gravity fed. The principal disadvan- length, depending on such factors as alloy, prod-
tages are slow cooling rates (Fig. 8), poor surface uct size, and equipment size. Commercial ingot
finish, and the minimum wall thickness of 4 mm. varies from 200×1000 mm to 600×1900 mm in
For the same alloy the slow cooling rate results cross section and is up to 9 m in length. The
in lower mechanical properties than with perma- maximum size of flat rolled products depends on
nent mold casting. Nevertheless, sand casting is alloy, temper, and thickness. Maximum size of
widely used, particularly if the casting is large flat plate may vary from 1300 to 5300 mm wide
or if the number of items to be produced does and 23 – 25.4 m long. The maximum weight per
not justify the expense of a metal mold. An ad- piece commercially available is about 10 000 kg.
vantage of sand casting is that quite complex Maximum size of flat sheet is 900 – 3350 mm
shapes can be made with alloys that are not par- wide and 4.6 – 19.8 m long. Sheet is also sup-
ticularly resistant to hot cracking because sand, plied in coils up to 2500 mm wide and 12 000 kg
unlike metal, can give when the alloy contracts in weight. Foil is supplied in coils up to 1900 mm
on freezing. wide.
Mill products or wrought products are produced Extrusions are produced in extrusion presses by
by working ingot into the desired shape. The forcing an ingot or billet to flow from a container
most common mill product is sheet, but signif- through a die to produce an elongated shape. The
icant quantities of plate, foil, extrusions, drawn diversity of shapes and sizes is great, ranging
tube, forgings, impacts, rolled rod, bar, shapes, from the simplest round rod to cross sections of
and wire are produced [5, Chap. IX]. great complexity. Table 7 summarizes the shape
and size capabilities of the aluminum extrusion
industry. Extrusions may be given thermal and
3.4.1. Plate, Sheet, and Foil mechanical treatments to produce the desired
temper, or they may be given further mechan-
Plate, sheet, and foil are collectively referred to ical deformation by drawing to tube or wire. Ex-
as flat rolled products. By convention, plate is truded stock can also be fabricated further by
thicker than 6.30 mm, sheet is between 0.15 mm forging and drawing.
18 Aluminum Alloys
Table 7. Capabilities of the extrusion industry
than 10 mm in diameter or between flats. It is
Alloy almost all commercial produced by drawing rod or bar through a series
wrought alloys of dies. Cable is made by stranding wire. ACSR
Section thickness 1 – 300 mm
Diameter of circumscribing 6 – 300 mm (aluminum conductor, steel reinforced) is made
circle (smallest circle that by stranding aluminum wires around steel wire.
completely encloses the shape)
Weight/length 0.07 – 300 kg/m
Impacts are parts made in a confining die
Straight length 33.5 m max. from a metal slug by a rapid, single-stroke appli-
Weight per piece 1200 t max. cation of force through a punch. The metal flows
Tubing and pipe diameter 600 – 840 mm
back along the punch or through an opening in
the punch or die.
The capability of extrusion presses is de-
scribed in terms of the maximum force that the
press can exert on the ingot or billet. Capac- 3.5. Powder and Paste
ity ranges from a few hundred to 13000 t, but
most presses fall in the range 1500 – 2500 t [3, Most aluminum powder is made by atomizing
Chap. 3]. molten aluminum with compressed air; the par-
ticle size is controlled by the atomizing condi-
tions. The particles are very rough but approxi-
3.4.3. Forgings mately equiaxial. Atomized powders are used in
a number of chemical and metallurgical proce-
Forging is metalworking performed in hammers dures.
and presses. The compressive force is applied ei- Pigments are usually produced by ball
ther locally – the different parts of the forging are milling atomized powder in the presence of lu-
progressively worked on open dies (hand forg- bricants to produce thin flakelike shapes hav-
ings) – or over the entire surface of the forging in ing length and breadth 10 to 100 times greater
closed dies (die forgings). Forging is done both than thickness. After milling, the pigment may
hot and cold. Starting stock is ingot or partly fab- be dried at moderately elevated temperature at
ricated forms such as extruded bar, rolled bar, reduced pressure, or solvent may be added to
and plate. Forging hammers range in capacity make a paste.
from 0.2 to 25 t and make parts weighing up
to 100 kg. Mechanical presses range in capacity
from 300 to 10000 t and make parts weighing up 4. Commercial Alloys, Products, and
to 25 kg with plan areas up to 0.3 m2 . Hydraulic Uses
presses range in capacity from 500 to 75000 t and
make parts weighing from a few kg to 1500 kg A number of systems are used throughout the
with plan areas up to 3 m2 [3, Chap. 5]. world to designate aluminum alloys and tem-
pers. In the discussion that follows, the Alu-
minum Association designations are used for
3.4.4. Other Mill Products casting and wrought alloys.
the right of the decimal point indicates product acteristic is affected significantly. Variations of
form: 0 for castings; 1 and 2 for ingot, 2 indi- the basic tempers are shown for heat-treatable
cating a narrower composition range within the alloys in Table 12. Additional digits, the first not
broader limits of the xxx.1 composition. A mod- zero, may be added to designation T1 through
ification of the original alloy or impurity limits T10 to indicate a variation in treatment that sig-
is indicated by a letter prefix. (I, O, Q, and X nificantly alters the characteristics of the prod-
may not be used as the prefix.) uct.
Table 8. Casting alloy designation system Table 10. Basic temper designations
201.0 S 4.6 0.35 0.35 0.70 Ag, 535 – 650 2.77 19.3 71.0
0.25 Ti
355.0 S or P 1.2 0.50 5.0 545 – 620 2.71 22.4 70.3
C355.0 1.2 0.50 5.0 545 – 620 2.71 22.4 70.3
356.0 S or P 0.32 7.0 555 – 615 2.69 21.5 72.4
A356.0 S or P 0.35 7.0 555 – 615 2.69 21.5 72.4
A357.0 S or P 0.60 7.0 0.15 Ti, 555 – 615 2.68 21.6 71.7
0.005 Be
360.0 D 0.50 9.5 555 – 595 2.63 21.0 71.0
380.0 D 3.5 8.5 540 – 595 2.74 21.0 71.1
390.0 D 4.5 0.60 17.0 505 – 650 2.73 18.0 81.2
413.0 D 12.0 575 – 582 2.66 20.4
B 443.0 S or P 5.2 575 – 630 2.69 22.0 71.0
513.0 P 4.0 1.8 Zn 580 – 640 2.65 24.0
518.0 D 8.0 535 – 620 2.57 24.1
520.0 S 10.0 450 – 605 2.57 25.0 66.0
713.0 S or P 0.70 0.35 7.5 Zn 595 – 640 2.81 24.0
852.0 S or P 2.0 0.75 6.25 Sn, 205 – 635 2.88 23.3
1.2 Ni
a
D for die casting, P for permanent mold casting, and S for sand casting;
b
Melting range m.r., density 25 , average coefficient of thermal expansion ᾱ over the range 20 – 100 ◦ C, and modulus of elasticity E
in tension;
c
Actual density slightly lower because of porosity
Table 14. Characteristics and tensile properties of die casting alloys
Resist- Fluidity Solidification Pressure Normally Corrosion Machining Polishing Electro- Anodizing Chemical Strength at Suitability Suitability
ance to shrinkage tightness heattreated resistance plating appearance oxide elevated for welding for brazing
hot coating tempera-
cracking ture
C355.0 11 1 1 yes 3 3 3 1 4 2 2 2 no
A356.0 11 1 1 yes 2 4 5 2 4 2 3 2 no
A357.0 11 – 1 yes 2 3 4 – 4 – 2 1 –
B 443.0 11 1 1 no 2 5 5 2 5 2 4 1 limited
520.0 24 5 5 yes 1 1 1 4 1 1 ∗ 5 no
713.0 54 4 3 aged only 2 1 1 2 2 3 5 4 yes
21
Table 16 lists tensile properties of some per- 4.3. Alloys for Wrought Products
manent mold and sand castings, minimum guar-
anteed values for separately cast test bars [30, Almost 400 domestic and international chemi-
ASTM B26, ASTM B108]. cal compositions have been registered with the
Castings are also ranked by product charac- Aluminum Association for wrought alloys [14],
teristics (Tables 14 and 15). Resistance to cor- and more than 1000 alloy-temper-product com-
rosion is based on general corrosion in a stan- binations have been described [6], [8].
dard salt spray test. Machining is a composite Nominal compositions are listed in Ta-
rank based on ease of cutting, chip characteris- ble 18. Typical properties that depend on com-
tics, quality of finish, and tool life. Polishing is position but not on temper are illustrated in Ta-
based on ease of polishing and quality of finish. ble 19. The melting range is for a thoroughly
Electroplating rank indicates the ability to take homogenized structure. The modulus of elastic-
and hold an electroplated coating. Anodizing ity is an average of tension and compression.
rank is based on lightness of color, brightness, The modulus is about 2 % higher in compres-
and uniformity of the clear anodized coating ap- sion than in tension.
plied in sulfuric acid electrolyte. The chemical Some characteristics and properties for se-
oxide coating is ranked on the combined resist- lected alloy-tempers are given in Table 20. Cor-
ance of coating and base alloy to corrosion. The rosion ratings A through E are relative ratings,
elevated temperature strength is based on ten- in order of decreasing merit, based on expo-
sile and yield strength up to 260 ◦ C. Die castings sures to sodium chloride solution by intermit-
are not generally solution heat treated, but some tent spraying or immersion. Alloys with A and
permanent mold and sand castings are. Castings B ratings can be used in industrial and seacoast
may be given a low-temperature aging or sta- atmospheres without protection. Alloys with C,
bilization treatment without a separate solution D, or E ratings generally should be protected,
heat treatment. at least on faying surfaces. The general corro-
Some uses of aluminum alloy castings are sion ratings of thick sections of 2011-T3, 2024-
listed in Table 17 (see next page). T3, and 7075-T6 would be lower than given in
Aluminum Alloys 23
Table 17. Typical uses of aluminum casting alloys
201.0 applications requiring highest strength and moderate elongations (T6): structural castings, aerospace parts, truck and trailer
castings. Applications requiring elevated-temperature strength (T6, T7): gasoline engine cylinder heads and pistons, rocker
arms, connecting rods; turbine and supercharger impellers; missile fins. Applications requiring high strength and energy
absorption capacity: gear housings, aircraft landing gear, ordnance
355.0 applications requiring good castability, high strength, and pressure tightness: pump bodies, liquid-cooled cylinder heads,
crankcases, aircraft fittings, impellers
C355.0 stronger and more ductile than 355.0: aircraft, missile, and other structural parts
356.0 intricate castings requiring good strength and ductility: transmission cases, truck axle housings, truck wheels, cylinder blocks,
cylinder heads, fan blades, marine hardware
A356.0 stronger and more ductile than 356.0: aircraft and missile parts, auto transmission cases
A357.0 aircraft and missile parts requiring weldability, strength, and toughness
360.0 applications requiring corrosion resistance better than 380.0
380.0 most widely used die-casting alloy: lawnmower housings, gear cases, cylinder heads for air-cooled engines, parts for auto and
electrical industries
390.0 auto cylinder blocks, four-cycle air-cooled engines, air compressors, parts requiring abrasion resistance, low thermal expan-
sion, or elevated-temperature strength
Table 20. The corrosion ratings of 5182 and 5456 in order of decreasing merit. Ratings A through
may be lowered by exposure to elevated temper- D for weldability, brazeability, and solderability
ature for long periods. also are relative ratings. For example:
Stress-corrosion cracking ratings are based
on service experience and laboratory tests of A) Generally weldable by all commercial pro-
specimens exposed to the 3.5 % sodium chlo- cedures and methods
ride alternate immersion test. B) Weldable with special techniques or for spe-
cific applications that justify preliminary tri-
A) No known instance of failure in service or als or testing to develop welding procedure
laboratory tests and weld performance
B) No known instance of failure in service, C) Limited weldability because of crack sensi-
limited failures in laboratory tests on short tivity or loss in resistance to corrosion and
transverse specimens mechanical properties
C) Service failures with sustained tension stress D) No commonly used welding methods have
acting in short transverse direction relative been developed
to grain structure, limited failures in labora-
tory tests of long transverse specimens A wide variety of alloy-temper-product com-
D) Limited service failures with sustained lon- binations are available as indicated by the par-
gitudinal or long transverse stress tial listing in Table 21. Some typical uses for
wrought aluminum alloy products are in Ta-
Ratings A through D for workability and A ble 18.
through E for machinability are relative ratings
24 Aluminum Alloys
Table 18. Nominal compositions and uses of wrought aluminum alloys
Si Cu Mn Mg Cr Ni Zn Others
5454 0.8 2.7 0.12 welded structures, pressure vessels, marine service, truck
panels
5456 0.8 5.1 0.12 high-strength welded structures, storage tanks, pressure
vessels, marine applications
5657 0.8 anodized auto and appliance trim
6005 0.8 0.50 heavy-duty structures requiring good corrosion resistance,
truck and marine, railroad cars, furniture, pipelines
6111 0.9 0.7 0.3 0.9 automobile body panels
6022 1.3 0.08 0.6 automobile body panels
Aluminum Alloys 25
Table 18. (Continued)
Si Cu Mn Mg Cr Ni Zn Others
6061 0.6 0.28 1.0 0.20 heavy-duty structures requiring good corrosion resistance,
railroad cars, furniture, pipelines, truck and auto wheels,
tooling plate
6063 0.40 0.7 pipe railing, furniture, architectural extrusions
6066 1.4 1.0 0.8 1.1 forgings and extrusions for welded structures
6070 1.4 0.28 0.7 0.8 heavy-duty welded structures, pipelines
6101 0.50 0.6 high-strength bus conductors
6151 0.9 0.6 0.25 moderate-strength, intricate forgings for machine and auto
parts
6201 0.7 0.8 high-strength electric conductor wire
6262 0.6 0.28 1.0 0.09 0.6 Pb, 0.6 Bi screw machine products
6351 1.0 0.6 0.6 heavy-duty structures requiring good corrosion resistance,
truck and tractor extrusions
6463 0.40 0.7 extruded architectural and trim sections requiring bright
finishing
7005 0.45 1.4 0.13 4.5 0.04 Ti, 0.14 Zr heavy-duty structures requiring good corrosion resistance,
trucks, trailers, dump bodies, sports equipment
7049 1.5 2.5 0.16 7.6 aircraft and other structures
7050 2.3 2.25 6.2 0.12 Zr aircraft and other structures from plate, forgings, or extru-
sion
7072 1.0 finstock, cladding alloy
7075 1.6 2.5 0.23 5.6 aircraft and other structures
7175 1.6 2.5 0.23 5.6 aircraft and other structures, forgings
7178 2.0 2.8 0.23 6.8 aircraft and other structures
7475 1.5 2.3 0.22 5.7 aircraft and other structures requiring high fracture tough-
ness
∗ Melting range m.r., density 25 , average coefficient of thermal expansion ᾱ1 over the range 20 – 100 ◦ C, and average modulus of
elasticity E
Table 20. Typical tensile properties, electrical resistivity, and product characteristics of some wrought aluminum alloys
26
Tensile properties Corrosion resistance Weldability
Alloy- Electrical Workability Machina-
Brazeability Solderability
temper resistivity, (cold) bility
Tensile 10−9 Ω m General SCC Gas Arc
Yield Elongation, % ∗
strength, strength, Resistance
MPa MPa spot & seam
1.6 mm 12.5 mm
thick dia.
1100−0 90 34 35 – 29 A A A E A A B A A
1100-H18 165 150 5 – 30 A A C D A A A A A
Aluminum Alloys
2011-T3 380 295 – 15 44 D D C A D D D D C
2011-T8 405 310 – 15 38 D B D A D D D D C
2024−0 185 76 20 20 34 – – – D D D D D C
2024-T3 485 345 18 – 57 D C C B C B B D C
2024-T861 517 490 5 – 45 D B D B D C B D C
2036-T4 340 195 24 – 42 C – B C – B B D –
2219−0 170 75 18 – 39 – – – – D A B D –
2219-T87 475 395 10 – 57 D B D B A A A D –
3003−0 110 42 30 40 34 A A A E A A B A A
3003-H18 200 185 4 10 43 A A C D A A A A A
3004−0 180 69 20 25 41 A A A D B A B B B
3004-H38 285 250 5 6 41 A A C C B A A B B
4032-T6 380 315 – 9 49 C B – B D B C D –
4043−0 145 69 22 – 41 B A – C – – – – –
4043-H18 285 270 1 – 41 B A – C – – – – –
5052−0 195 90 25 27 49 A A A D A A B C D
5052-H38 290 255 7 – 49 A A C C A A A C D
5182−0 275 140 25 – – A A ∗∗ A D C A B D D
5182-H19 420 395 4 – – A A ∗∗ D B C A A D D
5456−0 310 160 – 22 59 A ∗∗ B ∗∗ B D C A B D –
5456-H321 350 255 – 14 59 A ∗∗ B ∗∗ C D C A A D –
6010-T4 290 170 24 – 42 A A B C A A A A B
6061−0 125 55 25 30 37 B A A D A A B A B
6061-T451 240 145 22 25 43 B B B C A A A A B
6061-T651 310 275 12 17 40 B A C C A A A A B
6066−0 150 83 – 18 43 C A B D D B B D –
6066-T6 395 360 – 12 47 C B C B D B B D –
7005-T53 393 345 15 – 45 B B C A B B B B B
7050-T7451 510 455 – 11 43 C B D B D C B D D
7050-T7651 530 475 – 11 44 C B D B D C B D D
7075-T6 570 505 11 11 52 C C D B D C B D D
7075-T73 505 435 13 – 43 C B D B D C B D D
Alloy Sheet Plate Tube Pipe Structural Extruded Rolled or cold finished Rivets Forgings Foil
shapes wire, rod, and forging Fin stock Can sheet
bar, and stock
Drawn Extruded shapes Rod Bar Wire
1100 0 0 0 0 0 0 0 0 0 H112 0 0
H12 H12 H12 H112 H112 H112 H112 H112 H14 F H19 H14
H14 H14 H14 H14 F H12 H18
H16 H112 H16 F H14 H19
H18 H18 H16 H25
H113 H18 H111
H113
H211
2024 0 0 0 0 0 0 0 0 T4
T3 T351 T3 T3510 T3 H13 T351 H13
T361 T361 T3511 T3510 T4 T4 T36
T4 T851 T3 T3511 T351 T6 T4
T72 T861 T81 T81 T6 T851 T6
T81 T8510 T8510 T851
T861 T8511 T8511
3003 0 0 0 0 H18 0 0 0 0 0 H112 0 0
H12 H12 H12 H112 H112 H112 H112 H112 H112 H14 F H19 H14
H14 H14 H14 F F H12 H18
H16 H112 H16 H14 H14 H19
H18 H18 H16 H25
H25 H18 H111
H113 H113
H211
3004 0 0 0 0 H19
H32 H32 H34
H34 H34 H36
H36 H112 H38
H38
5052 0 0 0 0 0 0 0 0
H32 H32 H32 F F H32 H32 H19
H34 H34 H34 H32 H34
Aluminum Alloys
27
Table 21. (Continued)
28
Alloy Sheet Plate Tube Pipe Structural Extruded Rolled or cold finished Rivets Forgings Foil
shapes wire, rod, and forging Fin stock Can sheet
bar, and stock
Drawn Extruded shapes Rod Bar Wire
Aluminum Alloys
T4 T451 T4 T1 T1 H13 T4 H13 T6
T6 T651 T6 T4 T4 T4 T451 T4 T652
T4510 T4510 T451 T6 T6
T4511 T4511 T6 T651 T89
T51 T51 T651 T93
T6 T6 T913
T6510 T6510 T94
T6511 T6511
6066 0 0 0 F
T4 T4 T4 T6
T6 T4510 T4510
T4511 T4511
T6 T6
T6510 T6510
T6511 T6511
7075 0 0 0 0 0 0 0 0 T6 F
T6 T651 T6 T6 T6 H13 T6 H13 T73 T6
T73 T7351 T73 T6510 T6510 T6 T651 T6 T652
T76 T7651 T6511 T6511 T651 T73 T73 T73
T73 T73 T73 T7351 T7352
T73510 T73510 T7351
T73511 T73511
T76
T76510
T76511
Aluminum Alloys 29
Table 22. Designations of approximately equivalent casting alloys ∗ [31]
355 AP 309; H49−13 .SC 51N 3600; G-AS5CG; AC4D L78; LM16
G-AlSi5CuMg
C355 .SC 51P
356 AP 601 ∗∗; H49−18 .SG 70N 3.2364 3599; G-AS7GM; AC4C LM25
G-AlSi7MgMn
A356 BP 601; CP 601; H49−18 .SG 70 P 3.2374; G-AlSi7Mg; 5028; L99
GK-AlSi7Mg
360 AP 605; BP 605; H49−23 3051; 5074; GD-AS9GF;
GD-AlSi9MgFe
380 AP 313 .SC 84P G-AlSi8Cu3;
GD-AlSi8Cu3;
GK-AlSi8Cu3
A380 BP 313; H49−16 .SC 84N 3601; G-AS8,5C; LM24
G-AlSi8,5Cu
413 AP 401 ∗∗ .S 12P GD-AlSi12 LM20
518 AP 503; H49−19 .G 8 5080; GD-AG7,5F;
GD-AlMg7,5Fe
520 AP 505; H49−8 .G 10 3056; G-AG10; G-AlMg10 AC78 L53; LM10
∗ The Australian and Canadian designations refer to the Aluminum Association .2 alloys, whereas the German, Japanese, and British
refer to the .0 alloys. The Italian designations generally refer to both .0 and .2 alloys. For example, AP 309 is equivalent to 355.2 and L78
is equivalent to 355.0;
∗∗ AS for .1 alloys, e.g., AS 601 for 356.1
30
Aluminum Australia Austria Canada France Germany Italy Japan Netherlands Spain Switzerland United
Association Kingdom
Aluminum Alloys
UNE 38−320
3003 A3003 3003 A-M1 AlMnCu 3003 3003 AlMn1 L-3810 AlMn
3203 UNE 38−381
3004 A3004 A-M1G AlMn1Mg1 3004 L-3820
UNE 38−382
3105 AlMn0,5Mg0,5 N31
4043 B4043 4043 A-5S N21
5005 A5005 A-G0,6 5005 5005 AlMg1 L-3350 AlMg1 N41
UNE 38−335
5050 A-G1,5 L-3380 AlMg1,5
UNE 38−338
5052 A5052 5052 A-G2,5C AlMg2,5 5052 5052 L-3360
UNE 38−336
5056 A5056 AlMg5 5056 5056
5083 B5083 5083 A-G4,5MC AlMg4,5Mn 5083 5083 AlMg4,5Mn L-3321 AlMg4,5Mn N8
UNE 38−340
5086 A5086 5086 A-G4MC AlMg4Mn L-3322 AlMg4
UNE 38−341
5356 B5356 5356 A-5G
5454 A5454 5454 A-G2,5MC AlMg2,7Mn 5454 L-3391 AlMg2,7Mn N51
UNE 38−345
6061 A6061 6061 A-GSUC 6061 6061 L-3420 H20
UNE 38−342
6063 B6063 AlMgSi0,5 6063 6063 AlMgSi L-3441 H9
UNE 38−337
6101 B6101 E-AlMgSi 6101 L-3431
UNE 38−343
7072 D7072 L-3721
UNE 38−372
7075 A7075 AlZnMgCu1,5 7075 A-Z5GU AlZnMgCu1,5 7075 7075 L-3710 AlZn6MgCu1,5 2L88 ∗
UNE 38−371 2L95, 2L96
finishing characteristics
other techniques. Two categories of powder-
metallurgy products are made: high-perform-
catalytic reactions
wear resistance
ance wrought products, and sintered parts.
high strength
high strength
Comments
parts
loyed powders. Lubricant to prevent aluminum
adhering to compacting tools may be mixed with
Yield strength, Elongation, %
3
2
2
1
The part then is sintered in an inert atmosphere
at a temperature that causes limited melting to
promote interparticle bonding as well as alloy-
MPa
95
230
180
330
75
145
60
170
55
150
275
145
240
210
330
160
230
120
180
105
205
310
95
105
2.51
2.51
3.05
3.05
1.35
T1-sintered
T1-sintered
T1-sintered
T1-sintered
T1-sintered
Aluminum Products
T1-loose
Sintered
sintered
Temper
T6
T6
T6
T6
T6
T6
1.5
1.5
1.5
26.3
5.1. Shaping
Mg
1.0
0.5
0.6
2.5
4.0
0.5
1.6
1.0
Cu
0.8
0.4
1.0
Si
Alcan 76
Alcan 91
601AB
201AB
202AB
602AB
Alcoa
Alcoa
Alcoa
Alcoa
Alcan
Alloy
Figure 41. Preplating surface preparation sequence suitable for alloys 1100, 3003, 3004, 2011, 2017, 2024, 5052, 6061, 208,
295, 319, and 355
The multistep nature of finishing processes is 7) metal coatings (immersion and electroless
illustrated in Figure 40 by showing a sequence coating, electroplating)
for anodizing architectural parts [11, p. 590]. 8) painting and organic coatings
One sequence for preparing alloys for electro- 9) enameling
plating is shown in Figure 41 [11, p. 604]. Al-
though many methods are used, they can be di-
vided into nine categories:
5.3.1. Mechanical Cleaning and Finishing
1) mechanical
2) chemical cleaning Mechanical methods may be used to remove as-
3) etching perities, smoothing the surface, or to produce
4) brightening a uniformly rough surface. The method can re-
5) chemical conversion coating move metal (e.g., grinding, polishing, buffing,
6) anodizing blasting) or deform the surface (e.g., embossing,
hammering, shot peening). Surface appearance
Aluminum Alloys 35
ranges from mirrorlike to hammered, depending 5.3.4. Chemical and Electrolytic Brightening
on the method and alloy.
Chemical brightening, chemical polishing, and
bright dipping are synonymous. The rough sur-
5.3.2. Chemical Cleaning and Finishing face is smoothed and brightened by dissolv-
ing the high spots. Acid oxidizing solutions
Chemical cleaning and finishing treatments are
are used most commonly, for example, phos-
used to:
phoric – nitric and phosphoric – sulfuric acids.
1) Remove oxides, lubricants, and other matter The solutions can be tailored to specific alloys.
left on the surfaces from prior operations or Electrolytic brightening, or electropolishing,
storage also is used to produce smooth bright sur-
2) Smooth or roughen surfaces to impart spec- faces. The aluminum is the anode. A vari-
ular or mat appearances ety of baths are used, including fluoroboric
3) Develop decorative or protective coatings acid, sodium carbonate – trisodium phosphate,
4) Deposit metallic films and sulfuric – phosphoric – chromic acid. These
The surfaces that result from these treatments brightening processes are followed by desmut-
are usually a pretreatment for other finishes, but ting, anodizing, and sealing.
they are sometimes the final surface of the arti- The surfaces produced range from specular to
cle. diffuse. Generally the quality of finish is highest
The least aggressive cleaners are the organic for super pure aluminum (99.99 %) containing
solvents. They are used to remove oils and up to 2 % Mg and high-purity aluminum (99.7
greases but do not remove oxides or metal. Al- to 99.85 %). However, these finishing methods
kaline cleaners range from mild to aggressive. are also applied to other alloys: e.g., 5457, 5357,
They are commonly used to dissolve or remove 6463, 6063, 5052, 1100, 5005, 3003, and 6061,
dirt and can be formulated to etch. Etching is the quality of finish decreasing generally in this
controlled by inhibitors, such as silicates. Acid order.
cleaners are used to remove oxide films, welding
and brazing fluxes, and smut from other clean-
ing operations. Smut is a term applied to the 5.3.5. Chemical Conversion Coating
dark deposit formed when alloys containing high
concentrations of silicon, copper, iron, and man- Chemical conversion coatings are surface films
ganese are etched in alkaline solutions. formed by reactions that convert the surface of
the aluminum into one of the components of
the coating. Because the coatings are integral
5.3.3. Chemical Etching with the surface, they have excellent adherence.
Although conversion coatings are thinner and
Chemical etching removes metal to produce less protective than anodic coatings, they give
mat finishes and to reduce or remove surface adequate corrosion and abrasion protection for
scratches, extrusion die lines, and other small de- many applications and are excellent substrates
fects. Etching promotes surface uniformity, thus for lacquers, paints, plastic films, adhesives, and
simplifying subsequent finishing treatments. Al- lubricants.
kaline etching works well with most aluminum Many solutions have been used, but they gen-
alloys, provided etching is followed by desmut- erally contain agents to do at least two things:
ting. However, acid etching is preferred for (1) dissolve the original aluminum oxide coat-
99.99+ aluminum and alloys containing large ing and some of the underlying aluminum and
amounts of magnesium or silicon. (2) form insoluble aluminum compounds (ox-
The most common alkaline etching solution ides, phosphates, or chromates) on the surface.
is NaOH plus a sequestering agent to retard the Inhibitors are sometimes added to control the
formation of hydrated alumina. Acid etching rate at which aluminum dissolves.
solutions are usually nitric – hydrofluoric and
sulfuric – chromic acids. The high-silicon alloys
are also etched in hydrofluoric acid solutions.
36 Aluminum Alloys
Process bath Amount, wt % Tempera- Duration, min Voltage, V Current Film thickness, Appearance Remarks
ture, density, µm
◦
C A/dm2
Sulfuric acid
Sulfuric acid 10 18 15 – 30 14 – 18 1–2 5 – 17 colorless,
hard, unsuitable for coloring
Water 90 transparent
Alumilite
Sulfuric acid 15 21 10 – 60 12 – 16 1.3 4 – 23 colorless,
good corrosion protection
Water 85 transparent
Oxydal
Sulfuric acid 20 18 30 12 – 16 1–2 15 – 20 colorless, good corrosion protection, suitable for variegated and golden
Water 80 transparent coloring
Anodal and Anoxal
Sulfuric acid 20 18 50 12 – 16 1–2 20 – 30 colorless,
for coloring to dark tones, bronze, and black
Water 80 transparent
Commercial chromic
acid process
Chromic acid 5 – 10 40 30 – 60 0∗ 0.5 – 1.0 4–7 gray to good chemical resistance, poor abrasion resistance, suitable for
Water 95 – 90 iridescent parts with narrow cavities, electrolyte not detrimental
Eloxal GX
Oxalic acid 2 – 10 20 – 80 30 – 80 20 – 80 0.5 – 30 5 – 60 colorless to
hard films, abrasion resistant, coloring depends on alloy
Water 98 – 90 dark brown
Ematal
Oxalic acid 1.2 50 – 70 30 – 40 120 3 12 – 17 gray, opaque,
hard, dense film, extreme abrasion resistance
Titanium 1 enamel-like
potassium oxalate
Citric acid 0.025
Boric acid 0.2
Water 98
chosen
gray or bronze
light yellow to
light to dark
light to dark
Appearance
15 – 35
50
700
µm
A/dm2
28
20 – 75
10 – 75
ucts.
V
20 or 40
80
−4 to 0
18 – 24
1–7
ature,
10
◦
0.3 – 4
81 – 93
0.75
99.25
wt%
12
1
87
Sulfuric acid
Sulfuric acid
Oxalic acid
Oxalic acid
Water
Water
Water
Process
(MHC)
Lasser
226
Automotive
Bearings sheet none Pb + Sn + Cu 6 + 32 prevent seizing
Bumper guards castings buff and zincate Cu + Ni + Cr 2.5 + 51 + 0.8 appearance, corrosion resistance
Tire molds castings none hard Cr 51 wear and corrosion resistance
Aircraft
Hydraulic parts, landing gears, small engine pistons forgings machine and zincate Cu 2.5 + 25 + 76 wear resistance
flash + Cu + hard Cr
General Hardware
Screws, nuts, bolts castings buff and zincate Cd (on threads) 13, 0.5 on threads corrosion resistance
Spray guns and compressors die castings buff and zincate hard Cr 51 appearance
Window and door hardware die castings barrel burnish and brass 8 appearance, low cost
zincate
Household
Coffee maker sheet buff and zincate Cr 5 appearance, cleanness, resistance to food
Refrigerator handles, salad makers, cream dispensers die castings buff and zincate Cu + Ni + Cr 2.5 + 13 + 0.8 contamination appearance, cleanness, resistance to
food contamination
Personal products
Compacts, fountain pens sheet buff and zincate Cu flash + brass 5 appearance, low cost
Jewelry sheet buff and zincate brass + Au 8 + 0.25 appearance, low cost
Aluminum Alloys
39
40 Aluminum Alloys
Table 32. Compositions of frits
organic films. Optimum pretreatment is mul-
tistep and may include combinations of me- Constituent Composition, wt%
chanical cleaning, chemical cleaning, conver-
Lead enamel Barium enamel Phosphate enamel
sion coating, anodizing, and priming. Pretreat-
ment ranges in effectiveness from solvent clean- PbO 14 – 45 – –
SiO2 30 – 40 25 –
ing, marginal even for interior service, to anodiz- Na2 O 14 – 20 20 20
ing, which can give corrosion protection in se- K2 O 7 – 12 25 –
vere environments. Conversion coatings are ex- Li2 O 2–4 – 4
B2 O 3 1–2 15 8
cellent bases for organic coatings and laminat- Al2 O3 – 3 23
ing adhesives, and they provide some corrosion BaO 2–6 12 –
P2 O5 2–4 – 40
protection. F – – 5
Primer coatings are formulated specifically TiO2 15 – 20 ∗ ∗
to promote the adherence and performance of
∗ 7 to 9 wt % added to frit during mill preparation of the enamel slip
finish coats. Plastic coatings, e.g., vinyl, epoxy,
butyrate, polyethylene, and nylon, can be ap-
plied in thicknesses of 0.1 – 0.5 mm by melting
fine particles of resin on the surface to form a
6. Corrosion Resistance of
continuous film. Plastic films, e.g., poly(vinyl
chloride) and poly(vinyl fluoride), are bonded Aluminum
adhesively to aluminum.
Corrosion literature deals with the theory and
the many observations of the role of metallur-
5.3.9. Porcelain Enamels gical structure, environment, stress, and time [4,
Chap. 7], [8, pp. 204 – 36]. Most of the effort has
Porcelain enamel is a glass film fused onto the been pragmatic, and the information consists of
surface of the metal. The components of the systematic observations on the performance of
enamel, a mixture of glass and inorganic pig- a variety of alloys, tempers, and protective sys-
ment particles, or frit, are applied as a water sus- tems in natural and artificial environments.
pension. The part and the mixture are heated to The oxide that forms on aluminum is bonded
dry and fuse the frit. The frit must melt below strongly to the metal and reforms very rapidly af-
550 ◦ C, and its coefficient of thermal expansion ter damage in most environments. Consequently
must be close to that of the aluminum substrate. the corrosion resistance of aluminum is typically
Compositions of frits are complex, as illus- excellent, even though pure aluminum is more
trated by three examples in Table 32 [11, p. 511]. electropositive than all other structural metals
The lead-based enamels have high gloss and except magnesium and probably beryllium. The
good weather resistance. The phosphate base has stability region of the oxide is shown in a Pour-
a lower melting temperature but is not as resis- baix diagram of pH vs. potential (Fig. 43) [38].
tant to water. The barium enamels melt at higher Aluminum is protected by its oxide film, i.e.,
temperature and have good resistance to chem- it is passive, in the pH range 4 – 8.5. The exact
icals. range depends on the form of oxide, the rate at
Aluminum alloys for porcelain enameling which the oxide dissolves in the electrolyte, and
are limited by their melting range, chemical the temperature. Outside the passive range, in
compatibility with the glass, and strength af- both acid and alkaline solutions, aluminum can
ter firing. The commonly used alloys are 1100, corrode. However, in some cases, corrosion does
3003, 6061, 443.0, and 356.0. Surface prepara- not occur even outside the passive range if the
tion consists of (1) removing dirt, grease, and oil; oxide is not soluble in the electrolyte or if the
(2) removing thickened, irregular oxide films; oxide is maintained by a strongly oxidizing so-
and (3) applying a conditioning film. lution.
Aluminum Alloys 41
Cu Mg Si
Phase Potential, V ∗
However, potential differences can be used to
Si −0.26 advantage. Alclad products consist of a strong
Al3 Ni −0.52
Al3 Fe −0.56 core alloy clad with alloy anodic to the core,
Al2 Cu −0.73 usually by 0.08 – 0. 10 V Corrosion will pene-
Al6 Mn −0.85 trate the cladding but not enter the core; instead,
CuMgAl2 −1.00
MgZn2 −1.05 corrosion proceeds laterally as the cladding is
Al8 Mg5 −1.24 consumed. Table 37 lists alloy pairs used in Al-
∗ Versus 0.1 N calomel electrode clad products.
Aluminum Alloys 43
Table 37. Combinations of alloys in Alclad products
Cladding alloy
Core alloy ∗
Nominal composition, wt%
Alloy no.
Si Mn Mg Zn Cr
6.6. Ratings for Resistance to Corrosion be selected for suitability in the service envi-
ronment. Corrosion risks should be minimized
From the vast amount of detailed information by proper design of the part and the equipment
available, ratings of resistance to ordinary corro- in which it serves. Suitable protective finishes,
sion and to stress-corrosion cracking have been e.g., conversion coatings, anodized film, organic
compiled for a number of alloy-tempers (Tables paints, and films, should be chosen. In some
14, 15, and 20, also see [8]). These ratings are cases cathodic protection can be used.
useful, but the selection of the optimum alloy-
temper-product for a particular application is
many faceted and requires expertise. 7. Major Markets [25], [42]
The rating system for resistance to stress-
corrosion cracking has been expanded to ac- By far the greatest part of aluminum shipments is
knowledge that susceptibility depends not only in the form of aluminum alloys, and production
on alloy-temper but also on product form and of primary aluminum and consumption of alu-
the direction of sustained stress with respect to minum are the best indicators of the importance
the metallurgical grain structure. Generally, sus- of aluminum alloys.
ceptibility is lowest when the stress is longitudi- World production of primary aluminum is
nal, i.e., parallel to the major direction of metal summarized in Table 38, and per capita con-
flow. Susceptibility can be higher when stress sumption of aluminum in selected countries is
is normal to the major flow and parallel to the summarized in Table 39 (see page after next).
minor flow (long transverse). Susceptibility is The major markets for aluminum products
highest when the stress direction is normal to are shown in terms of use by major industries
both major and minor flows (short transverse) in the United States in Table 40 (see page after
[8, pp. 213 – 14]. next). To eliminate duplication, the figures ex-
clude intra-industry shipments for further fabri-
cation.
6.7. Corrosion Prevention
Methods of preventing corrosion are well de-
veloped [4, Chap. 7]. The alloy-temper should
Asia (cont.)
Iran 40 60 116 118
Japan 140 34 17 17
Korea, Peop. Rep. 10 − − −
Korea, Republic of 19 2 − −
Tajikistan b − − 235 198
Turkey 60 61 60 60
United Arab Emirates 155 174 247 245
9. Properties and Selection: “Stainless Steels, 28. E. F. Emley, Int. Met. Rev. 21 (1976) 75 – 115.
Tool Materials and Special-Purpose Metals,” 29. H. A. Meier, G. B. Leconte, A. M. Odok, Light
Metals Handbook, 9th ed., vol. 3, ASM, 1980. Met. (N.Y.) 2 (1977) 223 – 33.
10. Heat Treating, Metals Handbook, 9th ed., 30. 1983 Annual Book of ASTM Standards-Section
vol. 4, ASM, 1981. 2. Nonferrous Metal Products, vol. 02.02:
11. “Surface Cleaning, Finishing, and Coating,” Die-Cast Metals; Aluminum and Magnesium
Metals Handbook, 9th ed., vol. 5, ASM, 1982. Alloys, American Society for Testing and
12. “Welding, Brazing, and Soldering,” Metals Materials, Philadelphia, PA 1983.
Handbook, 9th ed., vol. 6, ASM, 1983. 31. W. F. Kehler: Handbook of International Alloy
Compositions and Designations, vol. III,
Specific References Aluminum Metals and Ceramics Information
13. Registration Record of Aluminum Association Center, Battelle Columbus Lab., Columbus,
Alloy Designations and Chemical Ohio, 1980.
Composition Limits for Aluminum Alloys in 32. Registration Record of International Alloy
the Form of Castings and Ingot, The Designations and Chemical Composition
Aluminum Association, Washington, D.C., Limits for Wrought Aluminum and Wrought
revised Aug. 1982. Aluminum Alloys, The Aluminum
14. Registration Record of Aluminum Association Association, Washington, D.C., revised 1 June
Designations and Chemical Composition 1980.
Limits for Wrought Aluminum and Wrought 33. R. M. Hart: Wrought P/M Alloys 7090 and
Aluminum Alloys, The Aluminum 7091, Aluminum Company of America,
Association, Washington, D.C., revised Jan. Alcoa Center, PA 1981.
1984. 34. Met. Prog. 124 (1983) no. 1, 45.
15. R. E. Spear, G. R. Gardner, Trans. Am. 35. R. Knoll: Materials and Processes –
Foundrymen’s Soc. 71 (1963) 209 – 15. Continuing Innovations [Proc. Conf.],
16. M. C. Flemings: Solidification Processing, Anaheim, CA, 12 – 14 April 1983, Society for
McGraw-Hill, New York 1974. the Advancement of Material and Process
17. C. E. Ransley, H. Neufeld, J. Inst. Met. 74 Engineering, Azusa, Calif., 1983, pp. 133 – 48.
(1947/48) 599 – 620. 36. M. S. Hunter, P. E. Fowle, J. Electrochem. Soc.
18. D. E. J. Talbot, Int. Metall. Rev. 20 (1975) 101 (1954) 481 – 85.
166 – 84. 37. F. Keller, M. S. Hunter, D. L. Robinson, J.
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