For a solution of chromimum phosphate when putting in to solution aluminum there is removal of the aluminum.
It is possible to prevent a galvanic cell, stop the etching of the aluminum, by putting in a sacrificial anode.
In this situation I have access to metals like tantalum, titanium, tungsten and copper.
Which one of these would stop the oxidation of the aluminum.
I have slightly familiar with electronegativity and I understand that aluminum is 1.6. I just do not know if you want some thing with a higher or lower electronegativity.