That depends on the gun. There are many Sigs, with alloy frames that have over 50,000 rounds on them and are still going strong. Aluminum 1911's I doubt would stand up to that much just due to the design and troque of the .45 ACP
The barrel is what supports the chamber pressure, so that is the limiting factor.
As far as the frame, if you run a proper spring for the gun it will be a non-issue. If you underspring the gun, then subject the frame to battering, then any of the materials are going to show wear. Aluminum is softer, so it will show accelerated wear. Even the standard aircraft grade T6061 Aluminum is about 1/2 to 2/3rds as hard as most of your gun steel.
Aluminum is harder than polymer, but polymer is elastic. Aluminum is 3 times as elastic as steel.
Ask yourself this ... have you ever seen an AR15 wear out it's aluminum components? It's got a forged aluminum lower and upper receiver, and is subject to considerably more deposits and rough conditions.
I don't see how an empty could come in contact with the feed ramp after firing - it's going to extract and eject up not down. And again, most feed ramps are integrated into the barrel anyway.