# DIY-ers... Why Brass & Aluminum instead of copper?



## kramer5150 (May 19, 2009)

Something I have always wondered... Why do you all use Aluminum and Brass for pills, colllars and internal thermal conductive parts? Why not copper to conduct heat from the emitter to the outer aluminum host body?

Some of my heatsinking designs at work (cooling SMT ASICS)... Have been very successful using copper instead of Aluminum for its lower thermal resistance. While brass is a no-no because its the poorest conductor of the 3 metals.

:thinking:


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## krazy89 (May 19, 2009)

hmm... sometimes i wonder too... but i think AL is good cuz it's cheap and lightweight... brass is good because it gives super silky threads... and cheap???

and... in the grand scheme of things... i don't know if u consider led's to need the optimal in thermal management... tho... it does help... 

my $.02

KraZy


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## kramer5150 (May 19, 2009)

I would think you can capitalize on the best of both materials... Copper inside to rapidly conduct, Aluminum on the outside for its cosmetics, durability and emissive properties.

:thinking:


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## Sgt. LED (May 19, 2009)

Are they worrying about the copper turning funky maybe? :shrug: No clue really.
No, brass does too.


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## krazy89 (May 19, 2009)

kramer5150 said:


> I would think you can capitalize on the best of both materials... Copper inside to rapidly conduct, Aluminum on the outside for its cosmetics, durability and emissive properties.
> 
> :thinking:


haha... if i yanked out 1 hair for every weird decision made by manufacturers... i'd be bald... a long time ago...

KraZy


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## bshanahan14rulz (May 19, 2009)

Is copper harder to machine accurately without deformation?

Sometimes I browse through the MMM forums and I don't have a clue what they're talking about over there, but I wish I had those cool toys!


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## kramer5150 (May 19, 2009)

bshanahan14rulz said:


> Is copper harder to machine accurately without deformation?
> 
> Sometimes I browse through the MMM forums and I don't have a clue what they're talking about over there, but I wish I had those cool toys!



Oh... maybe this is a better thread for the MMM forum? Mods please feel free to relocate, thanks.


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## saltytri (May 19, 2009)

bshanahan14rulz said:


> Is copper harder to machine accurately without deformation?



It's certainly harder to get a nice finish on copper.


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## Justin Case (May 19, 2009)

When I've done lathe work, brass and aluminum were much easier to machine than copper. Copper seemed to "smear" rather than chip. There is a free-machining copper grade.


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## N10 (May 19, 2009)

deleted


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## LukeA (May 19, 2009)

copper is soft and $$$.


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## Russel (May 19, 2009)

Copper is much more expensive. When ordering material for 2c and 2d maglites heatsink mods, I was going to get copper until I saw the price! I ordered aluminum instead at a fraction of the cost of copper. Brass is less expensive as copper as well. 

One of the biggest commercial motivators: cost.

Russ


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## wildstar87 (May 19, 2009)

Also at least for this DIY-er, I don't have a lathe, so I'm pretty much limited to whatever parts I can buy, and that's what's out there, for the most part.


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## John_Galt (May 19, 2009)

i thought there was a problem with joining copper and aluminum. My chemistry teacher said something about this earlier in the year... Don't they corrode when placed next to each other? Or something like that?


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## krazy89 (May 19, 2009)

John_Galt said:


> i thought there was a problem with joining copper and aluminum. My chemistry teacher said something about this earlier in the year... Don't they corrode when placed next to each other? Or something like that?


i think you're thinking about batteries?? but they would need to be submerged in an acid??

KraZy


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## Justin Case (May 19, 2009)

Galvanic corrosion. Any electrolyte will do. Water will undoubtedly have some ionic content.


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## Kestrel (May 20, 2009)

Justin Case said:


> Galvanic corrosion. Any electrolyte will do.


+1.

I thought that I might be able to contribute some relevant materials data:
*Thermal* Specific _Den _*“Thermal*
*conduct* HeatCap _sity _*volume”*
(W / mK) (J / gK) (g/cc)_ (J/ccK)​Aluminum *250* __0.85 ___2.7__ *2.3*
Brass..... *110* __0.38 ___8.6 __*3.2*
Copper... *400* __0.39__ 10.5__ *4.0*
Silver..... *430 *__0.23 ___9.0 __*2.1*
("thermal volume" would be the heat that a fixed-size part such as a volume-restricted heatsink will absorb, per degree rise in temperature) 

So on top of copper having greater thermal conductivity, a fixed-size part made of copper would also absorb the most heat per degree rise in temperature. However, aluminum really isn't all that shabby, due to its more-than-adequate thermal conductivity and unusually high specific heat capacity. The 'thermal volume' of a brass part is good only because of its relatively high density.

BTW FWIW I spoke with Mr. Malkoff a while back and asked him about the possiblity of his drop-ins being made with aluminum instead of brass and he replied that he couldn't get the soldering good enough with aluminum to get an adequate thermal path to the heat-sink. I don't know that much about soldering, but could brass be easier to solder to than copper?

Also, could issues such as the formation of undesirable intermetallic precipitates in the solder-to-copper joint create a worse situation over the long term than solder-to-brass or solder-to-aluminum, impacting thermal-cycling fatigue issues in any electrical interconnects? Just speculation...:shrug:

A complicating issue with regards to any small electrical contacts is the possibility of induced kirkendall porosity due to electrical currents over long periods of time, potentially impacting long-term reliability of the electrical connections. Possibly more of a theoretical concern than a real one in a device which sees far less overall use than semiconductor components in computers etc etc...
http://en.wikipedia.org/wiki/Kirkendall_effect

Really fun stuff to think about though. Guess what kind of nerdy engineer I am??


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## Benson (May 20, 2009)

bshanahan14rulz said:


> Is copper harder to machine accurately without deformation?


Definitely; copper cuts like chewing gum.

I'm not sure why brass is so popular for thermally-significant parts; it does cut nicer than aluminum (witness it's reputation for silky-smooth threads), but the conductivity is substantially worse. To me, a brass-bodied flashlight (nice looks, easy good threads, and lots of thermal mass) with an aluminum pill (conducts heat well out to the body) would make more sense than the other way around.

Of course, as expensive as it would be, an all-copper light would really be the best, and would look mighty nice, too.


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## yellow (May 20, 2009)

dont forget weight!

Aluminium wins in cost, weight and machinability and is not this bad in thermal transfer

.. as long as one does not have to solder anything to it, the best material

PS: Anodizing is also a plus for Aluminium. Relatively easy to do. Is there an equivalent treatment with copper?


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## dom (May 20, 2009)

Yes -as Yellow says.
Copper -heavy,expensive and reacts with Al.
Brass can be soldered to,less reaction to other flashlight metals.

I have noticed on some Al. pills that they have been soldered to.Always wondered how they did that.

Cheers
Dom


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## matrixshaman (May 20, 2009)

The Firefly had a threaded copper light engine which made this twist one of the smoothest I've seen. I really like the idea of copper inside the light in the way it was used in the Firefly. BTW copper prices are at their lowest in over 3 years. They have dropped to nearly half of what they were a year ago - at least on copper pipe and wire.


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## kramer5150 (May 20, 2009)

dom said:


> Yes -as Yellow says.
> Copper -heavy,expensive and reacts with Al.
> Brass can be soldered to,less reaction to other flashlight metals.
> 
> ...



x2... I have tried to solder aluminum... and absolutely could not (failed miserably). First attempt was with an 80 watt weller iron, no dice. Second try was with a 120w station at work... no dice. I ended up getting around it by direct driving the LED, and alleviating any need for body solder... so the project was not a total loss.


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## krazy89 (May 20, 2009)

kramer5150 said:


> x2... I have tried to solder aluminum... and absolutely could not (failed miserably). First attempt was with an 80 watt weller iron, no dice. Second try was with a 120w station at work... no dice. I ended up getting around it by direct driving the LED, and alleviating any need for body solder... so the project was not a total loss.


the trick to soldering on AL is to sandpaper the solder point... and then use flux on the spot... then solder right away... as the more time the bare AL is exposed to air... a layer of oxidation will form...

KraZy


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## Lighthouse one (May 20, 2009)

I've had fine results using thermal glue from DX or AA epoxy to attach a cree led to an aluminum heatsink. Even running at 1.4 amps...no problem transferring heat.


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## dom (May 21, 2009)

krazy89 said:


> the trick to soldering on AL is to sandpaper the solder point... and then use flux on the spot... then solder right away... as the more time the bare AL is exposed to air... a layer of oxidation will form...
> 
> KraZy



That sounds so simple and makes sense. I'll try that next time.I had the same luck as Kramer when i tried awhile ago 
Thanks.


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