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 Temperatures more fine oxidation peaks corresponding to the potential arrests with Mg in alloy Activation at higher Temperatures without Mg in alloy  8006 Håkon  Al-PbØystein 3005Andres 5180Andres “Alloy X”Håkon 3102Jan Tore 1100Håkon 1200Håkon

3 An example of activation from 3102 without Mg from Jan Tore, PhD work at high T

4 Surface activation from 8006 with Mg from the etched surfaces Polarization measurements of AA8006 etched in10 wt% NaOH 10s for 60s and desmutted in HNO 3 etched and desmutted etched o C 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 characterization as etchedetched; 450 C water quenched etched; 550 C water quenched

6 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. Potential, VSCE Current Density, mA/cm2 Anodic Behavior in 5% NaCl

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 characterization as received fully annealed temper 450 C water quenched 600 C water 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 500 and 600 C water quenched sample.

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

10 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, Mg 2 Pb  Particle size effect – lower the melting point Nanomat trace element, 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.