What metal best suited for one off machined plaque destined for desert environment?

Seeking to have a plaque placed in a historical site in the Upper Mojave Desert, where it will have to bear the extremes of the desert environment.
Can't afford having a custom plaque cast up, I'm thinking of CNC engraving the plaque myself, and wonder what would be the best material. Black anodized aluminum would fade over time in the scorching sun. Brass, I fear would corrode too much. Is there a bronze alloy that is relatively machinable and which could be obtained in flat plate, say, 8-1/2 x 11", maybe 1/4" thick?
Jon
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wrote:

You may get a more specific answer, but the classical casting alloy for bronze sculpture, plaques, etc. is plain tin bronze, also called gunmetal. I don't know if it's available in wrought forms.
Much of the exterior, architectural bronze is Muntz metal. That one *is* available as plates and sheets. Neither one of these is a joy to machine; they're in the 30% - 40% machineability range, compared to free-machining brass.
Good luck.
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Ed Huntress

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On 6/6/2013 1:48 PM, Ed Huntress wrote:

Muntz sounds like something I'd like to avoid.... But, didn't think of this first, maybe someone makes cast plaque blanks... Off to Google...
Thanks,
Jon
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wrote:

C464 sheet is available in 1/4 inch sheet and machines nicely. It has good corrosion resistance. Online metals has it, I believe. Eric
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On 6/6/2013 2:46 PM, snipped-for-privacy@whidbey.com wrote:

Thanks Eric, I'll go look that up!
Jon
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Wood / Concrete Mold. There is an organization that creates historic markers in just that manner.
Brass would probably be fine as would aluminum in the desert. I believe that plaque on the military WWII historic pyramid marker out at Horn is cast brass. Its still fully readable today. I would do it as raised lettering rather than engraved.

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wrote:

Id not use aluminum. It does occasionally rain out there. About an inch a year there abouts..and the caustic soils/dust will mix with the rain and eat the aluminum rather quickly.
Gunner

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On 6/6/2013 4:41 PM, Bob La Lonee wrote:

Have no ability to cast, and can't afford to pay someone to cast one. But I can lay one out, program it, and set it up in the mill when things are slow...

I'd rather have raised lettering, but I want to tell a short story, and that would be a whole lot of machining. All my immigration paperwork and medicals for Australia are in and I'm just waiting for approval. That could come as soon as 2 months, though likely more like 5+. So I don't have a huge amount of time to put into this...
I thought about clear anodized aluminum. Have a friend that laser engraving. He has some trick stuff you paint on a surface, go over it with the laser, and the beam melts it into the surface. Wash off the rest, and you have nice jet-black lettering. Probably very permanent and the clear ano wouldn't fade like black. But this is the desert, and at certain times of the year, could reflect too much sun to be read comfortably, meaning it wouldn't get read.
There is already one historical plaque on site, and I would like to have something that at least makes a feeble attempt to look similar...
Going to look at the stuff Eric suggested and also search on blank cast bronze plaques.
Thanks,
Jon
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Sorry, wasn't clear. They make a wood mold and pour a concrete marker. I suppose I should go look at one of their markers before I go on... There is one not to far from where my folks live.
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On 6/7/2013 11:23 AM, Bob La Londe wrote:

Ah, that sounds like it'd be way too big. I need to seek permission of the Navy at the least on this. It would be for Little Petroglyph Canyon within NAWS China Lake. I have sufficient references citing him as discovering the petroglyphs in 1929, to feel comfortable asking for a plaque to mention him. The base's own training manual for petroglyph tour guides credits him, among other sources. He was an early settler, rancher, and miner just east of the petroglyphs and there is a dry lake bed named for him (misspelled, which I am petitioning USGS to correct) and became the first civilian caretaker at Junction Ranch when NOTS was created. Lot of family history there. But I don't want anything ostentatious, just a modest credit, a small plaque perhaps set in a low concrete block at the entrance to the trail head. I have made a few friends there that are into the history and supportive of such recognition, so maybe...
Regards,
Jon
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wrote:

ALL bronze is machinable.
http://en.wikipedia.org/wiki/Bronze_sculpture
http://www.historic-scotland.gov.uk/informguide-bronze.pdf
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<snip>

Heh! Yes, machinable, but that's relative. If you haven't experienced manganese bronze, you haven't lived. Nasty stuff, Maynard. You certainly wouldn't want to make it your choice.
Leaded phosphor bronze is a pleasure. Trouble is, it's likely to be stolen. Copper alloys are subject to that.
Harold
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On 6/7/2013 1:21 AM, Harold & Susan Vordos wrote:

Not where this sign is going... deep inside NAWS China Lake. No civilians get to this site without guides. That is, if I get permission. But I want to have my idea fleshed out, including a CAD rendering of the plaque before I make my pitch.
I will look into this material, thanks!
Jon
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wrote:

By now you probably realize that there are many bronzes that are reputed to have good corrosion resistance. Given the environment you're talking about, it probably doesn't matter much which one you choose. Any of them should perform well.
As Harold says, when you add a few percent of lead to phosphor bronze, machineability goes from, in this case, 20% for plain 10% phosphor bronze to 80% for the leaded variety. And there appear to be only modest differences in corrosion resistance, according to technical specs.
All of the bronze I've machined comes from two propellor shafts that I scrounged from a marine scrap pile. One is purported to be manganese bronze. It probably is; it's a bugger to turn and drill.
The other was claimed to be "naval brass," aka "uninhibited naval brass," aka "inhibited naval brass," aka C454. It's a lot easier to machine.
Muntz metal, C454, and many other "bronzes" actually are plain yellow brass (60% Cu; 40% Zn), with a very small amount of another element. That's the inhibitor. In the case of C454, it's 0.8% or so tin.
These inhibitors usually work by changing the grain structure of the alloy. They don't work directly to form a barrier. And each one is specific to a particular environment. In the case of C454, it's to protect against dezincification in a wet environment, salt water or fresh. But that works for a wide variety of environments.
Gunner brought up an important issue for deserts: alkali dust. Alkalies will kill aluminum, and regular anodizing doesn't stand up to sandblasting of any kind. One assumes that includes dry deserts with some wind.
Bronze should be better. And forget the names "brass" versus "bronze." Some brasses have less zinc than most bronzes. The old names are meaningless in determining the material properties. Just think of all of them as copper alloys.
If it were me, I'd keep it simple and stay away from anything exotic. Some copper alloys are made for very specific environments. The older, general-purpose alloys, like plain tin bronze, Muntz metal, C454 (aka C45400) and so on will handle a variety of environments. Go with whatever you can get.
When it comes to machining, the real nasties are the aluminum bronzes. I'd stay clear of them.
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Ed Huntress

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On Fri, 07 Jun 2013 13:34:55 -0400, Ed Huntress
Wherever I said C454, read "C464". Sorry about that.
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Ed,
Thanks much for the input. The precise location is mostly sandy, with basaltic rocks, etc. But the lake bed at China Lake is not too many miles west, and it's probably alkaline. I thought anodize would provide protection. So aluminum is certainly out. That leaves the bronzes (and your correction on the C454/C464 noted), or the stuff my friend can laser bond to SS. I really want to do the bronze, since that's the norm for historical markers in the outdoors. In trying to find blank cast bronze plaques, I found there are tons of people doing this. I might solicit a quote or two on a cast one. It might not be as expensive as I was thinking... But as this would commemorate my grandfather, I really want to make it myself.
Regards,
Jon
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wrote:

It sounds like you've put a lot of thought into it Jon, and I hope it's successful.
Regarding aluminum and anodizing, basic, nearly pure aluminum (grade 1100) is quite corrosion resistant but is gummy to machine. And like all grades, it's chemically very vulnerable to alkaline environments. Acids and alkalis are things against which it will not protect.
Anodizing is just aluminum oxide. It's hard as hell, and you'd think it would be very abrasion resistant -- at least, in terms of hardness. But regular anodozing is too thin, and too porous, to stand up to much physical abrasion. So-called "hard" anodizing, which is no harder than regular anodizing, is just thicker and less porous. It's also kind of ugly, IMO, and it still won't stand up to much sand blasting.
Good luck finding what you need in bronze. It should be available.
--
Ed Huntress

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On many a historic site - the sign is in Bronze. It is tough stuff.
Bronzes can be made to resist sea water. Brass is soft and will decay in rains.
Get a marine Bronze and you will be in good shape.
Martin
On 6/6/2013 3:08 PM, janders wrote:

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