Having pores is not good for corrosion. The risk of localised corrosion inside the pore is high. the resason could be difference in Oxygen Content inside and outside the pore. Ist like pitting corrosion (ofcourse not the same). Also the net surface area exposed to environmentr is higher than non porous material meaning higher corrosion and existence of active passive area s higher leading various other forms of corrosion depending on the Environment.

I guess, it depends on the kind of porosity (closed or open). First is practically not that problematic, i.e. in case you can close the open porosity by surface-near melting you have a light material with perhaps similar corrosion. The problem with pores is simply the dramatic increase of surface reacting with atmospheric or other gases.

Increase in pore is directly proportional to increase in surface area and you do not have a passivity which eats away the material.