What can I use as a sacrificial electrode to stop the oxidation of aluminium? 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. 

Thanks
I think that you are interested in the corrosion protection of aluminum. You have basically two choices depending on your experiment setup.

You can use an impressed current protection or a sacrificial anode method. The sacrificial anode method uses a more reactive metal (less noble) in contact with the metal requiring protecting. The less noble metal reacts first within corrosive environment.

The impressed current protection uses electric current to charge the metal requiring protecting with excess electrons. It changes the electrode potential in the negative direction until the metal is not reacting.

If you want to use the sacrificial anode method look in the table where you are looking for metal that is positioned higher than your aluminium (is more electronegative - so non of the mentioned metals).

More useful information can be found here CORROSION PROTECTION OF METALS 
 or here metals.about.