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

[kramer5150]

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:

 

[krazy89]

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

 

[kramer5150]

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:

 

[Sgt. LED]

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

 

[krazy89]

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

 

[bshanahan14rulz]

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!

 

[kramer5150]

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.

 

[saltytri]

Is copper harder to machine accurately without deformation?

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

 

[Justin Case]

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.

 

[N10]

deleted

 

[LukeA]

copper is soft and $$$.

 

[Russel]

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

 

[wildstar87]

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.

 

[John_Galt]

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?

 

[krazy89]

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

 

[Justin Case]

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

 

[Kestrel]

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??

 

[Benson]

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.

 

[yellow]

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?

 

[dom]

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