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I'm not really sure where to post this question:

As a trombone player, I've never understood why aluminum is never used in brass instrument manufacturing. It's seldom mentioned on the internet either. Mutes and such are often made with aluminum and there's no problem with workability there. Even small things like cross-braces are never aluminum.

And I don't think is a cost issue (if anything, isn't aluminum cheaper than brass?). Sterling silver is used on a lot of trombones bells ("king silvertone"), so it can't be a cost issue.

Is it a durability issue? Aluminum can be very resistant to distortion (bike frames). In my experience, aluminum mutes (one of those cup/straight jo-rals) are extremely well built, so durability doesn't seem like an issue.

My guess is that it's a sound issue. Would an aluminum instrument sound too shrill? I always thought at the end of the day, material still makes less of an impact to the sound than shape does.

Am I just missing something really obvious??

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    In addition to any objective quality factors there may be, I would not underestimate the tradition point. I encounter this all the time, with string instrument players scoffing at my carbon cello. But the worst are, perhaps surprisingly, electric guitarists... “I don't like active pickups” – “urgh, that amp has a printed circuit board” – “I had to try 20 different 9V batteries till I found one that would work well with my germanium-transistor Fuzz” – “that guitar looks not vintage enough. I'd like an artificially aged version of it [i.e., worn-out fretboard, damaged varnish etc.]”...
    – leftaroundabout
    Jun 14, 2017 at 21:17
  • @leftaroundabout that is completely true. I daydream about buying one of those light carbon fiber trombones, but then I'm afraid I'll be ridiculed about it so often I won't even want to leave my house with it!
    – user41033
    Jun 14, 2017 at 23:40
  • Just a bit of thinking here: exactly what would become better by using a different metal. And what problems would it create in the making of the instrument. And how much more would you as player pay for the instrument. And how many players would pay the premium price.
    – ghellquist
    Aug 11, 2019 at 7:08

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Aluminum is an excellent engineering material and easy to machine, but high quality brass instruments are assembled and finished by hand, and aluminum is not so well suited to hand working.

Parts like mutes, with relatively simple shapes, can be "mass produced" easily and accurately by standard machine tool operations like die casting, extrusion, etc.

Brass is more ductile, and much easier to shape by hand hammering, etc.

The surface finish of aluminum might also be an issue. Though it may not affect the tone much, aluminum is a very reactive metal and the surface is always covered with a self-healing layer of oxide, which is difficult to polish and easy to scratch. This permanent oxide layer also makes it hard to finish the instrument by silver-plating, etc, and hard to hand-solder or braze without using higher temperatures than for brass.

In contrast to aluminum, brass is to some extent self-lubricating when used for moving parts like tuning slides, etc.

The surface of aluminum can be easily colored permanently by "anodizing", but that is not very useful for a traditional-looking instrument.

Aluminum has been used for "wind instruments" where appearance doesn't matter, for example large organ pipes - but even then zinc is usually preferred, because it is easier to attach the soft-metal parts of the pipe (alloys of tin and lead) which need hand adjustment for regulating the tone and tuning the pipe.

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    While the high-quality instruments may be produced by hand, surely that's only a small portion of the instrument market? Therefore, it sounds like it comes down to appearance and tradition.
    – Nathan Merrill
    Jun 14, 2017 at 23:11
  • Thank you for your input Alephzero. You mention that aluminum is much harder to solder or braze than brass. But I know some people get their bells screw mounted (so they can be changed in and out). So besides finishing issues, what's stopping a machined aluminum bell? It's a lot lighter too. ( with special finishing, could be a premium option like the silver tone :() )
    – user41033
    Jun 14, 2017 at 23:37
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    @TempestJ I can't see any reason why making a screw-on machined aluminum bell would be impossible. You just have to solve two "non-engineering" problems: (1) find customers for them ("lighter" might not mean "sounds better!"), and (2) deal with the fact that no existing instrument makers would have the capability to make them without investing in new machine tools.
    – user19146
    Jun 15, 2017 at 1:28
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    @NathanMerrill It's hard to get any direct information about how "mass produced" instruments (many from China) are actually made, but I would guess they are automating the traditional manual methods as much as possible, not doing something completely new. For example it makes little difference whether you scribe around a template and cut out the metal sheet for the main tube and bell by hand, or use a computer controlled laser cutter.
    – user19146
    Jun 15, 2017 at 1:30
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Check out this article about choice of brass instrument materials, authored by Renold Schilke.

Schilke discovered that the very best-sounding alloy for trumpet bells is beryllium bronze, but as beryllium is massively toxic and would probably poison any trumpet tech who had to work on it, any Schilke trumpet you buy nowadays with a "Beryllium" bell is actually pure copper.

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