# Which type of aluminium??



## LEDcandle (Feb 3, 2006)

I see 2011, 2024, 6061 etc... I know most of them are alloys of different strengths and stuff, but which is the best for heatsinking use?

Don't they sell pure aluminium out there? I seem to see only the alloys offered for sale. I guess I'll have to go for copper, which is better anyway? 

If anyone has links to a 'Aluminium code guide', pls pass it on. Thanks!


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## gadget_lover (Feb 3, 2006)

For the purposes of makinga heat sink, the exact alloy does not matter too much. Pure aluminum is not an ideal material, so it's alloyed to give greater strength or workability.

I like 2011 for turning; it works well. Many like 6061 for it's strength and ability to anodyze well.

Copper is slightly better than aluminum, but it does tarnish which can cut down of heat transfer. 

For your purposes, I'd not worry about it unless you are doing the calculations to get the exactly perfect balance of surface area to mating area to sink volume. None of us are really doing that.

Daniel


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## LEDcandle (Feb 3, 2006)

Thanks Daniel! I'm pretty easy; just trying to find out which one works best!


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## wtraymond (Feb 5, 2006)

Actually, copper has double the thermal conductivity of most aluminum alloys.

6061 has a thermal conductivity of 109 Btu/hr-ft-F (F=degrees Fahrenheit) and a thermal diffusivity of 9.28 sq in/min. 6063 is slightly better at 126 Btu/hr-ft-F. Both are common, strong, light-weight, inexpensive, electrically conductive (63% of silver), corrosion resistant, and machinable. Thermal diffusivity is the ability of a substance to adjust it's temperature to that of it's surroundings.

Copper and common copper alloys have a thermal conductivity of 226 Btu/hr-ft-F and a thermal diffusivity of 10.38 sq in/min. Copper is more than three times as heavy/dense as aluminum and slightly more expensive. It's weaker in yield, shear, and tensile strength than aluminum, but is more electrically conductive (97% of silver). Copper has excellent machinability and can be easily soldered (unlike aluminum).

Aluminum is almost as good as copper at dissipating the heat it absorbs into the air. But copper is much better at absorbing the heat from a source. This is why a copper heatsink inside an aluminum flashlight works SO well. The copper rapidly draws the heat in and, with good thermal contact, the aluminum quickly dissipates the heat into the air.


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## tino_ale (Feb 5, 2006)

Hi,

I've heard that 7075 aluminium would be the strongest one. Is that true?


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## gadget_lover (Feb 5, 2006)

Cool! and expert! I've been wanting to ask this question for a long time.

What's the formula for determining the proper thickness of a heatsink given the following;

A 3 watt Luxeon LED driven at 3 watts.
Known thermal conductivity of the heat sink and body
Known internal diameter of the flashlight body

I'd like to determine the minimum thickness that will conduct the maximum heat to the body.

An example would be 6061 aluminum in a 17mm body. The flashlight body weighing in at .8 oz (24 grams)

Many, Many thanks.

Daniel


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## Leef (Feb 5, 2006)

As I remember, the first digit in the number classification describes yield strength, so 7xxx is stronger than 6xxx, lots stronger than 2xxx. Also, some alloys weld well, some don't. After the type designation (e.g. 7075), there's often a heat treatment number: T0 for none, T6 for significant heat treating. Note that some of the harder alloys (e.g. 7075 T-6) can't be bent much before the crack. But that alloy has a higher yield strength than some steels.

Check out: http://www.matweb.com/index.asp?ckck=1


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## gadget_lover (Feb 5, 2006)

Per Machinery's handbook, the groups are baed on the major alloy element. It's defineitely not ordered by strength. 2011-t3 has 43 ksi yield where 6061-t6 has only 40.

The alloys;
2000 - copper
3000 - maganese
4000 - silicon
5000 - magnesium
6000 - silicon with magnesium
7000 - zinc

Again per machinerys... "Though less strong than the 2000 or 7000 alloys [6061] alloys posses good formability and corrosion ressistance with medium strength."

6061 does anyodize well and it's readily available.

Daniel


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## Pellidon (Feb 5, 2006)

We make things out of three basic alloy families where I work. 6061-T6 for the majority of our stuff. It is moderately durable but when we used it on some items that were subject to handling knocks and rubbing on surfaces it does not hold up well or long. It can dent up with repeated knocks very easily compared to 2024 or 7075.

If it is sheet metal and must be bent then we use 5052 H32 which we call forming stock. It is very soft and malleable. 

2024 T350 (I think) is almost spec wise the same as 6061 with the addition of Copper. The ranges of most of the alloy agents overlap. We have some raw aluminum parts that were made in the early 70's that have seen lots of use over the years and they have not lost much due to the banging around and sliding these particular parts get subjected to. Copper is also an alloy agent in silver coinage for those old enough to remember them. 10% Copper mixed in with Silver makes the coins hold up to pocket wear. 

Pure Aluminum is very soft and I don't think any is around or not much of it anyway. We did a job for some components that had to be made of pure aluminum. We had to send the shavings and drop off parts back to have more stock made. Once the grapevine found out of our job we got calls from every scrap metal dealer from LA to Bangor trying to "take our worthless scrap" off our hands. If the pure stuff is needed, it is made strictly to order. 

For flashlight wear and tear I think 2024 and 7075 ("aircraft grade") are probably the best choices. 6061 might be ok if it has time to age. Aluminum alloys can harden up some over time.


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## LEDcandle (Feb 5, 2006)

Thanks guys! Great info... I already placed orders though. I ordered some 6061 stock, and since this is for heatsinking and not the body, I guess it won't be subjected to knocks or anything.

I also ordered a bunch of copper!  

wtraymond, thanks for the informative thermal properties post. I did read up on this and I know Silver is the only thing (save diamond ) slightly better than copper, and both these are practically twice better than Alu. For thin rods, copper and alu prices were close but as they got larger in diameter and for the sheets, the price difference is quite glaring.

So I got small copper parts and larger alu parts. But I have no machine, so I think I'm gonna have to endeavour on hand-crafting everything (and I suck at that). Let's see how it goes....


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## PEU (Feb 5, 2006)

20 series aluminium are softer than 6061 and hard anodizes like [email protected]#$%p. Some like it for turning, but I find it "gummy" I prefer 60 series like 6061 or 6262.

Also 7075 is nice but, at least here, it cost twice as 6061 and not much more strenght.

My 2 cents (of peso)


Pablo


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## Pellidon (Feb 5, 2006)

We found out the hard way that at least 2024 is harder wearing than 6061. We have a machine where a person puts a disk of aluminum on a stainless or steel hub and they rotate it like a Rap DJ spins a record until it hits a stop. After three months, the 6061 disks all had a 1/16 to 1/8 groove worn where the inner hole rested on the steel hub. 20+ year old 2024 disks do not have a groove. Also one machine has a spring loaded plunger button of a soft plastic that presses against the edge of the aluminum disk. Again the 6061 developed depressions where the pad presses against the disk and there are holes near the edge of the aluminum. We had to replace over 100 disk assemblies at considerable cost because our purchaser switched alloys on us due to the cheaper price of 6061 over 2024. He is no longer our purchaser. 

Can't vouch for other 20 series alloys. Of course it also depends on the heat treat number of the alloy. Sometimes some 6061 T1 gets slipped into our supply and I have personally had a drill bit stick in the alloy like it was cast in around the flutes. T1 is a gummy forming stock mess and not for drilling. Drills plug up and it is a disaster. T6 is a harder treatment and machines very well. We use our 2024 raw so I don't know about anodizing finish. I wonder if the copper content causes it to not take well. 

7075 has more of a status icon value since it is called "aircraft grade" and some think that means superior for other uses. Mostly it is just ovrepriced.


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## tvodrd (Feb 5, 2006)

LEDcandle,

I hope you ordered CDA (Copper Development Association) Alloy 145 (Telerium Copper.) Pure coppers can be very gummy to machine/deburr! TeCu cuts almost like CDA 360 "free machining" brass. Good luck- you'd be surprised what is possible with a hacksaw, some files, and, heaven-forbid, a Mototool! 

Larry


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## LEDcandle (Feb 5, 2006)

Hi Larry,

I ordered from onlinemetals, it doesn't seem to say what kind of copper it is. I doubt its telerium though? Saw a thread about that (was it by yaesufmofo?) and I think its much more expensive.

Oh man, guess I'll find out when I start working on it. If the diameter is right, all I need to do is saw out the bit I need and file it flat (And drill holes). Won't need to do much else to it


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## HarryN (Feb 6, 2006)

You will be in for a really big surprise if you end with Cu intended for electrical applications. Machining it is quite - interesting. :laughing:


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## LEDcandle (Feb 6, 2006)

Oh man, sounds like something bad's gonna happen 
I found it, its copper CDA 110 ETP and more info here at matweb :-

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MCUAAF02

Looks like practically pure copper to me. 
Any comments on this copper?


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## yinou (Feb 6, 2006)

tino_ale:

For off-the-shelf aluminum alloys 7068 is stronger than 7050. It's yield is 90-100ksi versus 40-60ksi for 7075, both in T6511 temper; it is currently one of the strongest available in round barstock. It is also considerably harder than 7075 or the 'standard' 6061 alloy, about twice as hard at 190 Brinell (95 for 6061).


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## gadget_lover (Feb 6, 2006)

Hey Peu. Try some 2011-T3. It does not anodize well (due to the copper) but it turns very nicely and stands up well to wear. My EDC is made from the stuff. It is un-anodized and rides on my belt every day, totally unprotected. After a year of use it has a few surface marks but no scratches or gouges. 

LedCandle. All is not lost. You can do a lot of shaping with a file even on pure copper. It will load up the file's teeth but you can clear it with a "file card". A disk sander will also take off a lot in a hurry.

Daniel


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## cmacclel (Feb 6, 2006)

At my work

-6061 is used 99% of the time
-2024 is gummy and clogs cutters and mills the guys hate it.
-5052 is used when we need something bent.



Mac


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## b2eze (Feb 6, 2006)

I agree, copper is a PIA to machine! Sticky!!!!! Grabs drills, turning bits, and will break your tap in a heartbeat, but it sure is pretty when the project is done. And it does seem to conduct heat better than Al. I like 6061 aluminum and buy it exclusively.... but I do machine "junk" I pick up here and there for free! I haven't found a big difference in machining "junk" aluminum and store bought! Maybe the free stuff is 6061 too.... I'm no expert... just learning.


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## tino_ale (Feb 7, 2006)

yinou said:


> tino_ale:
> 
> For off-the-shelf aluminum alloys 7068 is stronger than 7050. It's yield is 90-100ksi versus 40-60ksi for 7075, both in T6511 temper; it is currently one of the strongest available in round barstock. It is also considerably harder than 7075 or the 'standard' 6061 alloy, about twice as hard at 190 Brinell (95 for 6061).


 
That's interresting!
Thanks for the info :wave:


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