Type of aluminium for amp chassis?

[GainFreak]

Hi,

Many years ago I ordered a 2mm aluminium chassis for one of my amps at a local metal shop but never paid attention what type of aluminium sheet was used. Now the shop is gone and I can't even ask. At that time I didn't even know so many different types were available.
Now I'm going for another one but from what I learn there are many types of different strength and machinability starting from 1050 and going up to 60xx and even 70xx. Those that are very strong would crack during bending at 90 deg so the question is (preferably according to your experience) which type of aluminium (4 digit designation number) is the best compromise between strength and machinability (bending)?

[Loogie]

I just ordered some 3003, .080", which I believe is approximately 2mm and bent it on my cheap brake. Nothing bad happened. It just bent. It was a little gummy when I drilled it, but it cleaned up just fine. My guess is that it will work fine for my amp chassis. I got it from Metals Depot.

[GainFreak]

Thanks for that info. So 3003 is on the list.
Which other types are OK?

[Loogie]

You might want to investigate 5052 and 6061. Based on my limited research 5052 looks like it might have better formability. I'm not sure that's a real word.

[GainFreak]

Thanks for that info.
It looks like I'll have to order several samples and find out myself how they bend.

[Rob's Radio-Active]

Thanks for that info.
It looks like I'll have to order several samples and find out myself how they bend.

6061 is probably the most common aluminum available. It is machinable and heat treatable. It can be annealed by heating to about 500-600 degrees F and water chilled to make it very soft for complex bends (though not usually necessary and must be careful not to warp it by uneven heating) and baked in the oven at about 450-500 degrees F for several hours and cooled slowly to return it to its springy-tough state. It will, over time, ( a few weeks) mostly return to its springy-tough state even without heat treating it.

cheers
Rob

[printer2]

6013 is a great aerospace alloy.

[GainFreak]

I just checked with my local supplier and they have 6082 T6 sheets which from what I read from the net is a good replacement for 6061.
It's listed as structural alloy for high stressed applications and with highest strength from the 6xxx family of alloys so I guess it would be good for amp chassis as well.
Below is a link from a manufacturer:

Aluminium Alloy - Commercial Alloy - 6082 - T6~T651 Plate


After some more reading it turns out that T6 alloys are not good for bending without preheating.

[Enzo]

Did you discuss your needs with that supplier as deep as the technical questions you are asking here? They should be in position to advise as to best suited material for your use as well as cost options. Would you be having them do the bending or do you plan to do the sheet metal work yourself?

[GainFreak]

Yes, I asked them and they said that the several types they have in stock would break if bended at 90deg. The bending will be done later after the laser cutting. The other laser cutting company offered a 1050 H24 type and said no problem about either cutting or bending.
I asked several other laser cutting services and metal shops about aluminum and was consistently offered the 1050 H24 material. Some of them haven't even heard about different types and others just refused to work on other types. This means that I will have to do the experiments myself provided I can score some samples because most of the companies would sell only by sheet which most of the time is 2 sq. meters.

[J M Fahey]

Iīve made my own chassis , front panels and heat sinks since forever, out of aluminum.
Think 47 years or so.

IF I talk my suppliers about 3030, 6060 or any other 4 figure code, theyīll go: HUH???? , WTF are you talking about?
Yes, if I buy aluminum made by some multinational Company (Kaiser Aluminum, ALCOA or AlCan) they probably us those codes at the Factory or to deal with a major Buyer, think Ford Motors or whatever, but for us mere mortals buying over the counter, aluminum quality is defined by intended use .... which if you think about is not bad at all.

I can basically order (and they understand what I need and give me the proper one)

1) sheet aluminum in any thickness, in 3 qualities:
* soft/extra soft, the kind which seems to be as soft as lead, way softer then copper, which is meant to be lathe turned/spun into pots and pans , light fixtures, even aluminum bottles for bikers.

* mid hardness/semi hard, the general purpose one, and what you get if you specify nothing else, good for shearing, punching and bending, even to 90 degrees , without cracking .

Practical example:
still flat punched sheet, 1.5mm thick (about 1/16")


already bent and stuffed:


the finished amp:


a simple L shaped chassis, notice it was bent 90 degrees with no problems at all.
I cheated on labelling, instead of painting and silkscreening (it was a 1 off not worth the hassle) i just had graphics plotted at a print house, on self adhesive vinyl.


* hard/extra hard aluminum , only suitable for punching and requires far higher pressure for that, but has sharp edges and is very rigid, canīt be bent without cracking.

Seat-of-the-pants testing an unknown sheet (I often find surplus sheets or pieces for peanuts at recyclers or junkyards): hold it hanging by the corner and hit it in the middle with a (metallic) spoon or similar object: the soft one will sound dull like hitting lead, the extra hard will ring like a bell or give a starp tick, and the usable aluminum one will sound like, well, "aluminum" ; once you hear it itīs easy to remember.

[GainFreak]

IF I talk my suppliers about 3030, 6060 or any other 4 figure code, theyīll go: HUH???? , WTF are you talking about?

Yeah, I know that face expression...

Seat-of-the-pants testing an unknown sheet (I often find surplus sheets or pieces for peanuts at recyclers or junkyards): hold it hanging by the corner and hit it in the middle with a (metallic) spoon or similar object: the soft one will sound dull like hitting lead, the extra hard will ring like a bell or give a starp tick, and the usable aluminum one will sound like, well, "aluminum" ; once you hear it itīs easy to remember.

Thanks for this tip!

As I already mentioned the most commonly used material around is 1050 H24 which is almost pure Al but somewhat hardened. It's widely used for almost anything. Even a 4 mm sheet bends at 90 deg without cracking.
Next most available material (but not so much) is 5754 and occasionally 2024 so I guess I'll stick to what's most available although I'm still eager to test those two materials if they agree to cut some small sample strips from the sheets.

[Enzo]

I plead total ignorance here, but I recall from many years ago, something called "aircraft aluminum". I have no idea what it means and would like to know. I also seem to recall from warnings and a small experience that getting a cut from the stuff would wind up with inflammation. I assume the oxides on its surface were mildly toxic to the dermal tissues. I think it was harder than "regular".

[hylaphone]

I am no metallurgist, but have used 5052 many times. It's easy to machine and bend, and strong enough for an amp chassis.

[J M Fahey]

Just checked on some local suppliers, and sheet aluminum is described as "99% pure Al" , so not exactly an "alloy" ... although of course it must have a designation number too.

On the contrary, aluminum complex extruded profiles (heat sinks, doors, window frames, etc.) imply some components are added to the mix to improve that kind of machinability and of course, aluminum meant for casting (including recycled engine blocks and such) by definition has a lot of additives, to lower fusion point but mainly to "jump" the "paste" intermediate state and be quite liquid to better fill molds.
If somebody melts/recycles and laminates this kind as-is will end up with brittle aluminum .... not forgetting it will have unavoidable impurities .
I have a supplier who custom makes aluminum sheet for me , in 1.5 mm thickness, sheets 43cm x 1 meter.

Booteek maker colleagues (you know the kind, all photocopy the same old 5E3 or whatever but are very creative on wood finish, wild tolexing or panelgraphics) and call me madman in my face
As in: "are you CRAZY? why do you have custom sheets made, why donīt you buy the f*cking sheets from a regular vendor?" but fact is:
1) I pay half what they do
2) standard size is 1 meter by 2 , large and unwieldy, and you require a large shear to cut them, or pre-reduce them to something usable with some saw; mine are easy to handle 1 meter long but more important are 43 cm wide, on which width I standardized my chassis and panels (unless Iīm making a Twin type 2 x 12" ).
Why 43 cm?
Because adding 2 x 2.5 cm ears (1" standard ones) *all* my amps and preamps become rack mountable without further ado, can also use same silkscreens, that gives me a huge advantage, I can offer rack mountable stuff with minimum expense or trouble.
In fact I can sell (at profit of course) a rack mounted preamp or power amp for what "they" pay for an *empty* rack mount cabinet (which here are very expensive).

Hereīs a home made rack cabinet:




in this case I used a thicker one piece front panel because it was a custom job anyway, not meant to fit in a tolexed cabinet.
Although it later brought customers in (as expected) and so it was housed in a standard chassis, together with power amp and supply.