7071-T7 -VS- 6061-T6 aluminum

[Midknight]

Whats the difference in T7 aluminum on the hardness scale? And how much heaver is it? And is it expensive?

But most important, how is its performance? Like dose it act as a better heat sink then you average T6?

 

[pullbangdead]

I can't find any data on 7071 aluminum.

I found several entries on 6061-T6 and several on 7075, but no numbers for 7071 in my minute of searching. I can look further later if you really want me to.

But really, heat-sinking performance shouldn't be much different with either of them. They'll both be polycrystalline metals with plenty of free electrons, and the free electrons are what contributes most to thermal conductivity. With normal applications, I doubt you would ever notice a difference in heatsinking capability. They will be different, but I bet you won't be able to tell without some better-than-necessary measurements.

One may be more difficult to machine, not positive without looking at the numbers, but they're still both aluminum, which means they're going to be relatively soft either way.

 

[RA_pierce]

I've been searching and I found this:
http://www.practicalmachinist.com/vb/showthread.php?t=148697

There is a link in the second post with some info.
Edit: You can look up pretty much any material there and it gives the heat capacity, thermal conductivity, and everything else.
Neat...

 

[pullbangdead]

^Well that would explain perfectly why there isn't any data on 7071, it doesn't exist, good to know.

 

[Midknight]

That answers that question. But what seems to be th difference between 7075-T6, and 7075-T7?

I also saw in one of those posts, someone talking about titanium, and how its a very nice metal for machining. Would titanium make a nice host for a laser?

 

[pullbangdead]

^Ti would be a heck of a lot more expensive, but you would certainly be the envy of a lot of people.

The difference between 7075-T6 and 7075-T7 is just the heat treatment it gets. It's exactly the same alloy, same composition, but different heat treatments. It won't be any heavier or lighter since they're the same composition. Their heat sinking capabilities should barely be any difference, I doubt you'd ever be able to tell a difference as far as thermal properties. Hardness, don't remember off the top of my head, but that should be findable on google. Remember hardness correlates directly to strength (yield strength, in particular; yield strength may also be called something like .2% offset strength or something like that). So if you see strength for both, you know how the hardness relates between them.

 

[RA_pierce]

No, the post about titanium was regarding springs.
Titanium might be harder to machine.
Aluminum also has better thermal qualities.
Edit: but yes, titanium would be badass.

If you look at the charts at matweb you'll see the differences.

They also have info on hardness but I don't feel like pasting all that.

I won't pretend I know what all this means:

 
Titanium   Metric     English
Specific Heat Capacity 0.528 J/g-°C 0.126 BTU/lb-°F
Thermal Conductivity  17.0 W/m-K 118 BTU-in/hr-ft²-°F

6061 Al
Specific Heat Capacity 0.896 J/g-°C 0.214 BTU/lb-°F
Thermal Conductivity  167 W/m-K 1160 BTU-in/hr-ft²-°F
Machinability    50.0 %

    7075 Al
Specific Heat Capacity 0.960 J/g-°C 0.229 BTU/lb-°F
Thermal Conductivity  130 W/m-K 900 BTU-in/hr-ft²-°F
Machinability    70.0 %

 

[Midknight]

So as far as heat sinking goes, Specific Heat Capacity, and Thermal Conductivity is something you want to be as high as possible?

Like the difference between 6061, and 7075 is 1160-BTU vs 900-BTU. I'm not sure witch number is better. The higher one, or the lower one. If its the lower the better then your right, Titanium would be bad ass.

Thanks guys,

 

[pullbangdead]

Yes, you want heat capacity and thermal conductivity to be high. "Best" heatsinking is not a simple thing, as lots of things come into play: heat into the metal (from source), heat through the metal (conductivity), heat out of the metal (to drain, or air), heat absorbed by metal (that's where the heat capacity comes in), it's a fuzzy picture. But generally, higher conductivity is better, and higher heat capacity is better.

Conductivity allows the heatsink to move the heat away from the diode, from source to drain, and for it to spread throughout the whole mass faster. Since it spreads through the whole mass faster, the energy coming in is distributed better, and there will be less localized heating.

As far as heat capacity, think of it as "how much energy I can put in to achieve the same rise in temperature". So, if heat capacity is higher, the heatsink will absorb more energy before the temperature rises, so it's a better heatsink.

 

[Midknight]

Yes, you want heat capacity and thermal conductivity to be high. "Best" heatsinking is not a simple thing, as lots of things come into play: heat into the metal (from source), heat through the metal (conductivity), heat out of the metal (to drain, or air), heat absorbed by metal (that's where the heat capacity comes in), it's a fuzzy picture. But generally, higher conductivity is better, and higher heat capacity is better.

Conductivity allows the heatsink to move the heat away from the diode, from source to drain, and for it to spread throughout the whole mass faster. Since it spreads through the whole mass faster, the energy coming in is distributed better, and there will be less localized heating.

As far as heat capacity, think of it as "how much energy I can put in to achieve the same rise in temperature". So, if heat capacity is higher, the heatsink will absorb more energy before the temperature rises, so it's a better heatsink.

Thanks for the info. It was very helpful.

 

[Midknight]

No, the post about titanium was regarding springs.
Titanium might be harder to machine.
Aluminum also has better thermal qualities.
Edit: but yes, titanium would be badass.

If you look at the charts at matweb you'll see the differences.

They also have info on hardness but I don't feel like pasting all that.

I won't pretend I know what all this means:


Titanium Metric English
Specific Heat Capacity 0.528 J/g-°C 0.126 BTU/lb-°F
Thermal Conductivity 17.0 W/m-K 118 BTU-in/hr-ft²-°F

6061 Al
Specific Heat Capacity 0.896 J/g-°C 0.214 BTU/lb-°F
Thermal Conductivity 167 W/m-K 1160 BTU-in/hr-ft²-°F
Machinability 50.0 %

7075 Al
Specific Heat Capacity 0.960 J/g-°C 0.229 BTU/lb-°F
Thermal Conductivity 130 W/m-K 900 BTU-in/hr-ft²-°F
Machinability 70.0 %

I now know what I will be using for my new laser project. It will be a very large hand held portable laser. And for the outside shell I will be getting a custom designed Titanium body. And as far as the heatsink that will be housing the array of laser crystals, 3 laser diodes, driver, and TEC will be done out of 7075 aluminum.

But what I'm thinking is making a separate heat sink for the 3 laser diodes out of copper.
I was trying to get the stats from www.matweb.com but I can't figure out how to use the search engine.[smiley=lolk.gif] Would you mind pulling up some info on copper. As far as Specific Heat Capacity, and Thermal Conductivity goes.

Thanks,

 

[Spyderz20x6]

Titanium is a bad heat conducter.
Your best bet for conducting heat is copper, and if you can afford it, silver.
Silver is the best thermal conducter out there, while copper is second best.