1

Surface activation by trace elements

• Effect of Pb on activation of aluminium - ØS

• Effect of Mg on activation of aluminium - YY

• Effect of other trace elements (In, Sn, Misch, Zr) - BG

2

Summary of surface activation by trace elements in our investigated Al alloy systems

Activation at lower Temperaturesmore fine oxidation peaks corresponding to the potential arrests

with Mg in alloy

Activation at higher Temperatures

without Mg in alloy

8006 Håkon

Al-Pb Øystein

• 3005 Andres

• 5180 Andres

• “Alloy X” Håkon

• 3102 Jan Tore

• 1100 Håkon

• 1200 Håkon

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An example of activation from 3102 without Mg from Jan Tore, PhD work

at high T

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Surface activation from 8006 with Mg from the etched surfaces

-1

-0,9

-0,8

-0,7

1,00E-03 1,00E-02 1,00E-01 1,00E+00 1,00E+01

Current Density, mA/cm2

Po

ten

tial

, V

SC

E

Polarization measurements of AA8006etched in10 wt% NaOH 10s for 60s and desmutted in HNO3

etched and desmutted

etched + 450 oC 2h WQ at low T

5

GD-OES depth profiles for 8006 alloys 10s etched in 5% NaOH and desmutted for 60s in concentrated HNO3; then with different annealing conditions.

GD-OES characterizationas etched etched; 2h @ 450 C

water quenched

etched; 2h @ 550 Cwater quenched

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Anodic behavior of alloy 8006 as function of annealing temperature. All polarisation curves were recorded at least twice in order to ensure reproducibility of the plotted results.

Po

ten

tia

l, V

SC

E

Current Density, mA/cm2

Anodic Behavior in 5% NaCl

-1

-0,9

-0,8

1,0E-03 1,0E-02 1,0E-01 1,0E+00 1,0E+01

7

GD-OES depth profiles for 8006 alloys at different annealing conditions. Mg exhibits significant enrichment at the surface. Pb peak broadening with increasing annealing temperature.

GD-OES characterizationas received

fully annealed temper 2h @ 450 C

water quenched

2h @ 600 Cwater quenched

8

TEM characterization of the stripped oxides

At increasing annealing temperatures, more Mg segregated to the surface and formed the flake-shape Spinel (MgAl2O4) crystalline phases.

TEM bright-field micrographs of the stripped oxide film from 2h @ 500 and 600 C water quenched sample.

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Phase diagrams

L.F. Mondolfo, Aluminium Alloy, p563, 1976J.M. Eldridge et al., Trans., Metall. Soc. AIME, 236, p102, 1966

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Conclusion Remarks

Surface “passivation” effect by Mg-Spinel phase

Mass Mg diffusion would promote Pb surface segregation

possible to form a new low melting point phase, Mg2Pb

Particle size effect – lower the melting point

Nanomat trace element, http://www.nt.ntnu.no/users/yingday/NanoNFR

All of these seemed suggest 8006 activated at “a relative lower temperature” which motivated:

A ternary Al-Pb-Mg model alloy is investigating for getting a more clear understanding of the Mg effect.