Not only are steels alloys, there is no guarantee they won't crack, either. There are long running threads reporting the issues of guns used on a rental range in Las Vegas which spell out the longevity of firearms used there. Many see over 100,000 rounds a year, which reveal the long term affects of shooting.
Steel AK receivers tend to crack at the read near the stock attachment, but AR's never seem to have any cracks in the aluminum receivers. It's a matter of intelligent design for both - the first was intended to be built as inexpensively as possible on third world equipment, the second as a showcase of first world aeronautic abilities used in firearms.
Another example would be Glocks, which crack under the ejection port. For some reason the Gen 4's crack there much more often than Gen 3s. Take that with a grain of salt, again, 100,000 rounds are being fired.
How the gun was designed and if it was really intended to be used over a long service life as a duty pistol has a lot to do with it. The Commander series Colt designed in the early 50's was intended to be an aluminum alloy frame, Alcoa was the foundry which shipped them the first versions. That was a gun intended for the Army Pistol Trials of 1954, and it was submitted for testing in 9mm.
It took another 30 years to exhaust the fleet of 2.5 milllion 1911's to adopt an aluminum framed service pistol in 9mm - and the M9 doesn't have a reputation of problems with the alloy frame. It's the steel slide and locking bits which initially had issues, and the steel magazines which later on needed refinement.
We've gone from steel frames, to aluminum alloy frames, to polymer frames, and it's the engineering which is more important. Glocks don't have any issues with polymer failure, but there are some cases of the first generation LCP's cracking frames at the rear under the slide. It took extensive shooting to produce it. What has to be asked is whether a small pocket pistol was even intended to pass 50,000 rounds thru it? For the most part, no. Same for the duty weapons, is 100,000 rounds a reasonable expectation? Considering a twenty year service life and the number of rounds used to stay familiarized with it, that's over 400 rounds a month.
For many who carry on duty, that's a bit high, for a lot of us, it's uncomfortably expensive. Much less the fact we'd even keep shooting just one gun for 20 years.
I'd choose the gun for it's intended purpose, and let lighter weight with alloy or polymer fall where it helps or not. Carry? Yes. Range? Not so much, all steel is the demonstrated superior construction, and it's done well in duty sized guns for holster carry, too. Why? It has more mass to reduce recoil and makes for a faster shooting, more accurate gun. It does weigh more and that can be a good thing, on todays market the cost and carry advantage of the alternates is what is focused on.
