Aluminum and Its Cast Alloys
Aluminum and Its Cast Alloys
Aluminum and Its Cast Alloys
Designation
number
Pure aluminum (> 99.00 % Al) 1xx.x
Al Cu alloy
2xx.x
Al Si with Cu and/or Mg alloy 3xx.x
Al Si alloy
4xx.x
Al Mg alloy
5xx.x
Al Zn alloy
7xx.x
Al Sn alloy
8xx.x
Al other elements
9xx.x
The important alloying elements are Silicon, Silicon with added
copper/magnesium, Copper, Magnesium, Zinc, Tin, and Lithium. Alloy series
6xx.x is unused.
Properties:
high ductility,
They are weld able. However, because of their narrow melting range, they require certain
considerations in order to produce acceptable welding procedures.
When considered for fabrication, these alloys are selected primarily for their superior
corrosion resistance such as in specialized chemical tanks and piping or for their
excellent electrical conductivity as in bus bar applications
Excellent workability
Properties:
Due to copper Subsequent aging will increase strength and hardness
while decreasing elongation.
Its creep resistance improves by adding 2% nickel in aluminum copper
alloy.
The alloys in the 2xxx series do not have as good corrosion resistance
as most other aluminum alloys They have good mechanical properties
Copper improves machinability of aluminum by increasing its strength.
Alloys in this series are good for parts requiring good strength at
temperatures up to 150 C (300 F).
Al - 4% Cu alloy 195:
This alloy used in solution heat treated conditions and contain only 4% Cu. It
gives both strength and ductility.It used as sand cast for rare-axel housings
and fly wheels, bus wheels, air craft wheels and crank cases.
Al 8 % Cu alloys 112, 113, and 212:
Si presents in these alloys in a controlled amount which increase the fluidity
of the aluminum alloy and decreases its melting point. Due to increased
fluidity these are used for casting of thin sections such as housings, cover
plates and hydraulic brake pistons. These alloys are not age hardenable.
Alloy 356 (7 % Si 0.3 % Mg), Alloy 357 (7 % Si 0.5 % Mg) & Alloy
359 (7 % Si 0.6 % Mg):
Mg2Si is produced by the reaction of Si and Mg which is a hard phase and
gives strength.
Applications where excellent cast ability and good weld ability, pressure
tightness, and good resistance to corrosion are required.
Applications are: aircraft pump parts, automotive transmission cases, aircraft
fittings and control parts, water-cooled cylinder blocks.
Properties:
Iron impurities decrease the ductility of the materials.
Increased strength without unduly decreasing ductility
Corrosion resistance, good weld ability
Increased tendency to crack during hot rolling
Si is added to aluminum for strengthening and also to improve cast ability. About 5 to
12% is added for thin and complex castings.
Solidification time increases by the increase of silicon contents up to 12 % and also its
liquidus temperature decreases.
Ductility of these alloys is maximum at 12% silicon contents and then decreases down to
15 % silicon contents.
The density of aluminum decreases to 2.34gcm-3 when silicon contents up to 10% and
then slightly increases.
It reduces Al Si alloy coefficient of thermal expansion.
However excessive Si content produces difficult to cut and abrasive
material.
2 % Ni is added to these alloys for improved creep resistance and
mechanical strength.
Description of some commercial alloys is as follow:
Alloy 413 and alloy 443:
These alloys contain 12 % Si and 5.2 % Si respectively. These alloys are used
for intricate castings, food handling equipment and marine fittings.
Miscellaneous thin-walled and intricately designed castings. Other
applications where excellent cast ability, resistance to corrosion, and
pressure tightness are required.
Properties:
Good corrosion resistance and weld ability.
Alloys, containing more than 3.5% of magnesium, are susceptible to
stress corrosion at elevated temperatures. This problem can be
reduced by addition of Zn 1-2%mold release properties for die casting
and Poor casting properties.
Mg2Si provides the strengthening. That is produced by the combination
of silicon with Mg.
Mg has greater solubility in aluminum up to 14.9% but these cannot be
age harden able alloys.
Applications:
i. Architectural components. Sheets of 5xxx alloys also forms the surface of geodesic dome
structures, as in this example of a water treatment plant.
ii. 5xxx alloys are commonly used as external facing sheets of composite aluminum-plastic
structural panels,
iii. Aluminum cans have ends of alloy 5182, making that one of the largest volume alloys in
production.
iv. Automotive structures are likely to employ increasing amounts of 5754-O formed sheet for parts
such as internal door stiffeners or the entire body-in-white.
Rugged coal cars are provided by welded 5454 alloy plate construction
Properties:
Solution treatment followed by either artificial or natural aging allows considerable
increasing the yield strength (3-5 times).
Ductility of the alloy decreases as a result of the heat treatment.
Alloys of this series possess high mechanical strength combined with good formability
and corrosion resistance.
Temperature of artificial aging of 6xxx alloys is 320-360F (160-182C).
Due to addition of Mn It improves low cycle fatigue resistance.
Properties:
Aluminum-zinc-magnesium alloys are heat-treatable.
Alloys of this series possess the highest mechanical strength when heat treated.
Corrosion resistance of aluminum-zinc-magnesium alloys is good particularly in the
alloys containing small amount of copper.
Weld ability and formability of the alloys are quite good if the total amount of the
alloying elements is below 8%.
Small amounts of zirconium, chromium and manganese may be added for obtaining
fine structure and inhibiting recrystallization during solution treatment.
The zinc substantially increases strength and permits precipitation
hardening.
Highest UTS is obtained by adding 1.5% Zn.
Other alloys within this series are often fusion welded with excellent
results.
7Zn-0.9Mg-0.13Cr:
5.8Zn-0.6Mg-0.5Cr-0.2Ti:
References: