Aluminum Lecture

Report
Materials for Civil and
Construction Engineers
CHAPTER 4
Aluminum
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Aluminum



Primarily used for containers, packaging, aircrafts,
and automobiles.
In civil projects, primarily used for architectural and
finishing elements like doors, windows, and siding
with a small amount used for electrical wiring.
Not used extensively for structural members:

expense

strength and ductility

coefficient of thermal expansion
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In many beam design problems
deflection is a limiting criteria. Assume
a rectangular simply supported beam,
and the height of the beam is fixed by
other design considerations, determine
the difference in width required for an
aluminum beam compared to a steel
beam.
x
W
h
b
2x
Which reduces to:
The equation for the deflection in a beam is:
W (2 x) 3

48EI
Using the subscripts a and s for aluminum and
steel respectively, and using equal deflection for
the aluminum and steel beam:
W ( 2 x) 3 W (2 x) 3


48Ea I a 48Es I s
Ea I a  Es I s
For a rectangular section the moment of
inertia is:
I
1 3
bh
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By substitution and ha = hs:
ba 
Es
bs
Ea
Since Es = 29E6 and Ea = 10.5E6
Ba = 2.76 Bs
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Aluminum Advantages






Most plentiful metal on
earth
One-third the density of
steel
High strength-to-weight
ratio
Good thermal and electrical
conductivity
Anodizing or hard coating
for protection
Weldable alloys

Easy to recycle

Corrodes slightly but
does not rust

High reflectivity

Can be die cast

Easily machined

Nonmagnetic

Nontoxic
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Aluminum Production
Chapter
4:Materials
Aluminum
Mamlouk/Zaniewski,
for Civil and Construction Engineers, Third Edition. Copyright © 2011 Pearson Education, Inc.
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Crushing and Grinding
Four tons of bauxite are required
to produce 2 tons of alumina.
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Extraction
Al(OH)3 + Na+ + OH- ---> Al(OH)4- + Na+
Böhmite and Diaspore:
AlO(OH) + Na+ + OH - + H2O ---> Al(OH)4- + Na+
Ores with a high Gibbsite content can be processed at 140 ° C.
Böhmite requires 200 - 240°c.
(At 240°c tl the pressure is approximately 35 (atm))
Although higher temperatures are often theoretically advantageous there
are several disadvantages including corrosion problems and the
possibility of oxides other than alumina dissolving into the caustic
liquor.
After the extraction stage the insoluble bauxite residue must be
separated from the Aluminium-containing liquor by a process known as
settling. The liquor is purified as much as possible through filters before
being transferred to the precipitators. The insoluble mud from the first
settling stage is thickened and washed to recover the caustic soda, which
is then recycled back into the main process.
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Precipitation
Crystalline aluminium trihydroxide (Gibbsite), conveniently named
"hydrate", is then precipitated from the digestion liquor:
Al(OH)4- + Na+ ---> Al(OH)3 + Na+ + OHThis is basically the reverse of the extraction process, except that the
product's nature is carefully controlled by plant conditions, including
seeding or selective nucleation, precipitation temperature and cooling
rate. The "hydrate" crystals are then classified into size fractions and fed
into a rotary or fluidised bed calcination kiln. Undersize particles are fed
back into the precipitation stage.
Calcination
"Hydrate", is calcined to form alumina for the aluminium smelting
process. In the calcination process water is driven off to form alumina:
2Al(OH)3 ---> Al2O3 + 3H2O
The calcination process must be carefully controlled since it dictates the
properties of the final product.
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Filtration-Hydration
Filtration, such as vacuum drum or pressure filters, remove the silica and
low solids from the clarified alumina bearing liquor.
The liquid containing the dissolved alumina is pumped to tanks called
crystalization or precipitation tanks. The liquid is cooled with water from
the counter current decantation thickeners, and as it cools, alumina
hydrate slowly precipitates from the tank, according to the formula:
The precipitated liquor containing the white alumina is then filtered,
to remove the solid alumina from the liquid, using vacuum drum filters
or rotary pan filters, where it can be washed as it is filtered.
The alumina hydrate (AlOH3) is then dried. It can be further calcined
to Al2O3, alumina, in a rotary kiln at 800 defrees F.
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GHGs from Primary
Aluminium Production
Alumina Production
1.5 – 2.5 t CO2eq/t Al
IAI average = 1.9
Electricity Input
15.6 MWh/t Al
0 – 20.8 t CO2/t Al
IAI average = 5.8
Feeder
Gases
Anode
Electrolyte
Molten
Aluminium
Cathode Block

PFC Generation
0.02 – 24.5 t CO2eq/t Al
Global average = 1.26
Anode Carbon
1.7 – 2.1 t CO2eq/t Al
IAI average = 2.0
Source: IAI Life Cycle Inventory Data
IAI 2003 PFC Survey
GHG from Primary Aluminium Production
Two PFC (perfluorocarbon compounds - CF4 and C2F6)
contribute about 40% of direct primary aluminium GHG emissions
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Designation System for Aluminum
Alloys
Wrought* Aluminum Alloys
Alloy
Series
1xxx
2xxx
3xxx
4xxx
5xxx
6xxx
7xxx
8xxx
9xxx
Description or Major
Alloying Elements
99.00% Minimum Aluminum
Copper
Manganese
Silicon
Magnesium
Magnesium and silicon
Zinc
Other element
Unused series
Cast** Aluminum Alloys
Alloy
Series
1xx.x
2xx.x
3xx.x
4xx.x
5xx.x
6xx.x
7xx.x
8xx.x
9xx.x
Description or Major
Alloying Elements
99.00% Minimum Aluminum
Copper
Silicon plus copper and/or magnesium
Silicon
Magnesium
Unused series
Zinc
Tin
Other element
*worked by being forged or hammered
**poured into a mold to give it its shape
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Stress-Strain Properties of Aluminum
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Tensile Strength of Aluminum
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