Most frames made of metal are welded together, so I don’t really understand the comment about that.

Otherwise, yes, there are different grades of aluminum and different quality levels within a manufacturer’s line. However, even a relatively cheap aluminum frame can be pretty good. I ride a commuter bike that retailed for about $550… Aluminum frame, single speed with relatively cheap components, etc. i’ll bet that the manufacturer sourced the frame from China for about $35… And it is damn good. Light enough, stiff, rides beautifully.

One of my riding buddies is on a 25-year-old Trek with an aluminum frame... it’s been ridden hard and put away wet often. The kid is a very strong rider and really hammers the hell out of it. And it is still in great shape