As several previous posts have already stated. It won't rust, since there's no iron or steel in there, but it will oxidize odd colors. You could possibly sand it then coat it in some sort of sealer to keep it from oxidizing.
As to your intentions to buy a WE 1911, I'd highly advise against it. WE pistols are low quality to start with and their 1911 model is especially bad. They have a high tendency to rip themselves to pieces, literally. If you're looking for a full metal 1911 at a decent price I would recommend KJW.