Study about the corrosion behavior in 2050 T3 Al-Cu-Li ally when is used the Friction Stir Welding gor joint as a improved technique comparing with the usual (Laser, TIG, MIG, etc...). This procedure permits the union in semi liquid phase below the melting pint, it suppresses the defects related to the solidification and the contribution of externar matter. There are different parts in the weld: Heat Affected Zone, Termomechanic Affected Zone, Metal Base and Nugget Zone. With the movement of the matter in this procedure appears the pehnomenon "onion ring", bands of corrosion in the plane L-TC in the NS. For a better compression of the corrosion Microscopy for find out the free potential or the known Work Function of the material testing how it depends with the topography and time. With a test of an Open Circuit Potential and a camera is analyzed the chages in the material with the corrosion in the T3 and the post-welding T8 in a micrometer scale. For a better understanding of the corrosion behavior, another tests are done comparing the Work Function with the Corrosion Potential in ductile materials (Cu, Pb, Sn Al, Ti= and hard materials (Invar, 718, 625, 316L, AI203,AIN). It is demostrated tht there is a correlation with this two parameters that puts in order of novelty this materials.