Z-Michigan
Member
What are AK receivers made of?
As already noted, steel. Probably something comparable to 4130 or 4140. US-made AKM stamped receivers are typically one of those two grades.
But 4140/4150 in the AR15 context has nothing to do with the aluminum receiver, instead with the barrel material. And as I already stated, if you don't have the happy switch, it's unlikely to matter in the real world. Notably S&W uses 4140 in their AR15 barrels.