Brass is used because it is durable. So the connections would be brass but like I added above aluminum is much better for heat transfer.
Trane Corp. uses aluminum coils on evap. coils for efficiently transferring heat. Other companies are jumping on the bandwagon to meet SEER ratings.

Even if it was copper, it would take you half a day getting to it! Without the proper tools it would be like a monkey on a football!