Enhancement of Corrosion Resistance of Amorphous Aluminum Alloys
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Transcript of Enhancement of Corrosion Resistance of Amorphous Aluminum Alloys
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Contentsy Introduction
y Corrosion resistance in aqueous solutions.
y Corrosion rate for binary alloys.y Pitting potential curves of Al alloys.
y Potentiodynamic polarization curves of Al alloys.
y Corrosion rate for ternary alloys.
y Conclusions
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Introductiony The major serious problem for Aluminum and its alloys is
the pitting corrosion in aqueous chloride containing
environments.
y The corrosion resistance can be improved by alloying with
the corrosion resistant metals such as Ti, Zr, Nb, Ta, Cr,
Mo, W.
y However , melting points of some of these metals are far
higher than the boiling point of aluminum , hence alloys
with them cannot be prepared by conventional techniques.
y Non-equilibrium alloying methods have been used to
increase the amount of solute in solid solution.
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Corrosion resistance in aqueous solutions.
Structure of sputter deposited aluminum
alloys identified by X-ray Diffraction Corrosion rates of sputter-deposited
aluminum alloys in 1 M HCl at C as
function of alloying additions.
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Open circuit potential as a function of alloying
elements
Open circuit potential after immersion for 1 h in 1 M HCl at C
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Pitti Pote ti l s f ctionof lloying ele ents
Pitting potenti l of v rious Al
lloys in de re ted 0.1 M N Cl t
pH 10
Pitting potenti l of v rious Al lloys
s functionof concentr tion lloying
ele ents in 1 M HCl t C
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polarization & pitting potential curves of Al alloys.
Al Ti alloys
Anodic polarization curves of sputter-
deposited amorphous and argon melted
crystalline Al- 36 Ti alloys
Change in pitting potential of sputter-
deposited and arc-melted Al-Ti alloys
as a function of alloy Titanium
content.
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Al Zr Alloy
Potentiodynamic polarization curves of Al-
Zr alloys in de-aerated borate-boric acid
solution containing 0.5 M Nacl at 25 C
Change in pitting potential of sputter-
deposited and argon-melted Al-Zr
alloys as a function of alloy zirconium
content.
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Al -Ta, Al - Nb alloys
Potentiodynamic polarization curves of amorphous Al-Ta, Al-Nb alloys
measured in 1 N HCl at C.
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Al- Cr alloy
Corrosion rate of Sputter deposited Al-
Cr alloy in 1 M HCl Solution at C
Potentiodynamic polarization of
Sputter deposited Al-Cr alloy in 1
M HCl Solution at C
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Al Mo alloy
Anodic polarization curve for Al and
Al-6 at % Mo in deareated & Air
saturated 0.1 N KCl at pH of 8.
Anodic polarization curve for Al Mo
& Al W alloys in aerated 0.1 M KCl at
a pH of 7
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Al - lloys
Pourb ix di gr ms f or ndAl P ssivityof the
lloy is chieved in neutr l & cidic conditions
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Anodic polarization Al W alloys
Anodic polarization bheaviour of Al-3.6 W
alloy as a function of pH compared to pure
W and pure Al in 0.1 M KCl. Anodic polarization curves for Al
alloys in deareated 0.1 M KClSolution.
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Anodic Polarization characteristics of Al-alloys in 1 M
HCl at 30 Deg C
Al-Ti Active-Passive Transition -------- Pitting
Al-Zr Spontaneous Passivation -------- PittingAl-Ta Spontaneous Passivation -------- Pitting
Al-Nb Spontaneous Passivation -------- Pitting
Al-Mo Spontaneous Passivation ------- Active Dissolution
Al-W Spontaneous Passivation ------- No Pitting but
high current density
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Corrosion r te f or ternaryalloys
The Corrosion rate ofamorphous aluminum alloys in 1M HCl at Cas a function
of the total fractionofalloying elements
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Potentiodynamic polarization curvesof amorphous Al-Ti-Ni, Al-Cr-Ti, & Al-Cr-Mo alloys in 1 M HCl at C
Potentiodynamic polarization curves ofAl-Ti-Mg alloys in de-aerated borate-boric acid solution containing 0.5 M Nacl
at C
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Corrosion rates for Al-Cr-Ti alloys
Corrosion rates of the Al-Cr-Ti Alloys in 1 M HCl open to air at C as afunction of alloy chromium content.
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Open Circuit potential of Al-Cr-Ti alloys.
Open circuit potential of the Al-Cr-Ti Alloys in 1 M as a
function of alloy chromium content at C.
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Conclusionsy Al-Ti alloy has the low corrosion resistance & the
corrosion rate of this alloy are almost the same as that of
the aluminum metal, regardless of titanium content.
yAl-Ti, Al-Zr, Al-Nb and Al-Ta alloys suffer pitting byanodic polarization, but their pitting potentials are
higher than that of the Aluminum metal.
y Al-Mo, Al-W alloys show high resistance to the pitting
corrosion.y The difficulty of enrichment of alloying metal cations in
the passive film is responsible f or the susceptible to
pitting b y anodic polarization.
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y The amorphous Al-Ti-Ni, Al-Ti-Cr, Al-Cr-Mo shows
lower corrosion rates and higher pitting potentials in
comparison with the Al-Ti, Al-Cr binary alloys.
y The addition of small amount of magnesium to an
amorphous Al-Ti alloy containing a relatively small
amount of Ti leads to the enrichment of Ti in the passive
film which shows the better corrosion resistance.
y In ternary alloys the passive film contains Cr and Ti
oxyhydroxides which are more stable than the Al
oxyhydroxides in acidic or chloride solutions.