Just to make sure I understand your question:
You want to measure (?) whether the precipitate would act as an anode or cathode with respect to the host phase (Aluminum alloy 7075 in this case)?
I guess I would try to probe the Fermi levels with PES. The idea is that, the higher the Fermi energy, the less energy might be needed to get an electron out of the material, hence it might act rather as an anode.
However, it can be put upside down in a real electrochemical setup. E.g. if you have an electrolyte with ions, it depends on the energy that the ions have in each of the phases.
The Fermi energies then might only play a role in the respective ion-dissolution/incorporation rates.
If you know which kind of electrolyte to use, then take the material as work electrode, put it into the electrolyte containing the ionic species you are interested in. Then put a large Counter-electrode on the other side and apply some potential, run cyclic voltammetry or make a polarization measurement (slowly increase current). The current should be such, that the ions will have to go into your material.
If the ions in the electrolyte are positively charged, then the phase (aluminum alloy or precipitate) which ends up with a higher concentration of the ion-species is likely to be the more cathodic material. If the ions are negative, the material with the higher concentration is likely the anode wrt to the other phase. Of course this is only valid for the very electrolyte you use in experiment.
Hope I could help
Thomas
check the link below. It may help
http://download.springer.com/static/pdf/390/art%253A10.1007%252Fs12613-015-1057-3.pdf?originUrl=http%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs12613-015-1057-3&token2=exp=1455044237~acl=%2Fstatic%2Fpdf%2F390%2Fart%25253A10.1007%25252Fs12613-015-1057-3.pdf%3ForiginUrl%3Dhttp%253A%252F%252Flink.springer.com%252Farticle%252F10.1007%252Fs12613-015-1057-3*~hmac=d3ba7e658d59bbc29b07b312d8682c175900dd6bd7cf4a487ddbdb54addad56c
It may help you:
http://www.sciencedirect.com/science/article/pii/S092583880600538X
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