Welding copper heatpipes to aluminium fins - how to?

Tzupy · Post by **Tzupy** » Thu Oct 27, 2005 6:10 am

As the title says, I'd like to find out reliable information about this topic. People I spoke to told me it's not difficult to weld copper to copper, but didn't know about copper to aluminium.
I need this kind of information to advance from my heatsink concepts to working prototypes.
Thank you.

GlassMan · Post by **GlassMan** » Thu Oct 27, 2005 7:24 am

Don't know about welding, but usually solder would be used, or braizing if more strength was needed.
the welding eqipement usually available is much to large, and welding doesn't flow to cover all the contact surfaces like solder.
Do copper and aluminum melt at appx the same temp, if not you can not weld them. Alulminum is welded by a MIG welder I believe
http://www.lincolnelectric.com/knowledg ... t/alum.asp
This, maybe? http://www.muggyweld.com/
or http://www.jwharris.com/welref/faq/#Diss
Joining aluminum to copper?
Solder - Alsolder 500 and Stay-Clean® Aluminum Flux.
Brazing - Not recommended. Use steel transition piece between aluminum and copper.
Coat on steel end with aluminum. Braze coated steel to aluminum with Al-braze 1070. Braze uncoated end to copper with a Safety-Silv® brazing alloy.

Mats · Post by **Mats** » Thu Oct 27, 2005 8:35 am

GlassMan wrote: Do copper and aluminum melt at appx the same temp, if not you can not weld them.

Melting points
Al: 660° C
Cu: 1085° C

Aris · Post by **Aris** » Thu Oct 27, 2005 9:07 am

i think the way most heatsink company's do copper/aluminum is either solder them, or like when they put a copper core inside a block of aluminum they freeze them so they shrink slightly, slide them together then when they warm up to room temp they expand and dont come apart. but i'm pretty sure that process is a little beyond the average joe to do, so i think soldering is your best option.

Tzupy · Post by **Tzupy** » Thu Oct 27, 2005 9:22 am

Thank you for the replies, soldering it is.
I never heard of the Alsolder 500 and Stay-Clean® Aluminum Flux.
If they have bad thermal conductivity this would mess up the product.

GlassMan · Post by **GlassMan** » Fri Oct 28, 2005 7:48 am

ASlsolder is a solder made for aluminum, flus is an acid that thouroughly cleans the metal (solder and weld will not stick to non bare metal) and boils off.
they are just examples, home depot probaly has what you need

Tzupy · Post by **Tzupy** » Fri Oct 28, 2005 9:27 am

The composition of Alsolder500 is 85% tin and 15% zinc. Melting point is ~250C. Now, zinc has a thermal conductivity of ~30% that of copper, but I don't know how conductive tin is. I suppose one should use a larger amount of Alsolder to compensate for the poor thermal conductivity.

EndoSteel · Post by **EndoSteel** » Fri Oct 28, 2005 1:24 pm

Tzupy
Be careful, heatpipes explode if overheated. There's also a good chance of melting the solder а pipe is sealed with (-> dead pipe). I would suggest using low melt alloys (90-150C) if there are any of them that stick to aluminum well.

Ryan · Post by **Ryan** » Fri Oct 28, 2005 2:03 pm

Or, you could use thermal epoxy to glue them on. No heat, holds just fine, trasfers heat. without welding.

Post by **MikeC** » Sun Oct 30, 2005 9:51 am

If you examine all the heatpiped-heatsinks around, you find that >50% are not soldered or welded. Instead, they are usually clamped using mechanical tension/pressure or press-fitted. The Scythe Ninja's fins, for example, are simply press-fitted. Ditto the Zalman 9500, the Arctic Cooling Freezer. Press-fitted means the holes in the fins are just big enough to allow the heatpipe to slip through them but small enough so there's a lot of friction to hold them in place.

If press-fitting is good enough for these high performance HS...

Tzupy · Post by **Tzupy** » Sun Oct 30, 2005 11:02 am

Thank you for the reply, MikeC. I didn't expect the fins to be kept in place like that. I wonder if this could cause a major loss in thermal conductivity.

ronrem · Post by **ronrem** » Tue Nov 01, 2005 10:09 pm

Tzupy wrote:Thank you for the reply, MikeC. I didn't expect the fins to be kept in place like that. I wonder if this could cause a major loss in thermal conductivity.

It sounds like the Zinc/Tin solder is more apt to reduce conductivity. That with the tight fit style you'd need very exact tolerances. some framed designs would be held togather by the external frame. That,or the Thermal epoxy would be most apt to work for a homebuilt.