Tirod pretty much has it nailed, but read this:
http://cheaperthandirt.com/blog/?p=8
4 hours is not enough time to rust anything with the use of corrosive primers (ammo) alone. You are not dealing with a China doll. If it is actually an AK-47; it is a time-proven tool that will operate for a long, long time. The photos of the Somali rifles should give one an idea of how much abuse an AK-47 can take. And I would like to bet the AK-47 rifles the Somali's could afford were slap wore out by the time they got Em.
I have a Chinese SKS, late 60's as I recall, and it still has a world war left in it. My brother ruined a Rugger 7.62 ranch rifle with corrosive primed ammo; took at least 15 years to do it in the dry air of So Cal. I'll bet he didn't clean it but once every couple of years shooting hell out of it.
I would not use WD-40 on a firearm. I have seen WD-40 flash rust steel overnight - I swear I have no clue what is in WD-40, but it can react real weird when used with other products. I don't use it for much anymore... Keep a can in my tackle box in case I got to pull a hook out of myself; works good as an antiseptic on rusty hooks... go figure. The only bloody thing I like about the stuff anymore.
On to the next Caper,
CarolinaChuck