Enhancement of Corrosion Resistance of Amorphous Aluminum Alloys

8/4/2019 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.

Enhancement of Corrosion Resistance of Amorphous Aluminum Alloys

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