It's aluminum.
We saw a beautiful stainless arch on a 40 just ahead of ours at the old PSC factory, but when we inquired about one for our boat, we were told that the arch had cost over $12,000. That wasn't in the budget for us--our aluminum arch weighs considerably less and cost about $2500. Yeah, we have to keep at it with the touchup
paint, but we had other things to do with the extra money.
Still--the stainless would have been nice....
Sue