Aluminum Soldering

On Mon, 02 Jul 2012 13:50:23 -0700, Gunner Asch wrote:


Oh. So you can post a link -- great. I'm waiting for it.
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On Fri, 29 Jun 2012 11:23:17 -0400, Joseph Gwinn

Nonsense.
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Ned Simmons

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In article

Interesting book and webpage. I think I'll read the book.
The issue is not that one cannot braze metal X to metal Y. For the most part, you can braze anything to anything. The issue is that if one does not design to handle dissimilar temperature coefficients, the joint will soon tear itself apart.
This is a big issue in high reliability engineering, especially in the engineering of packages for semiconductors. There is an accelerated-aging MIL-SPEC test for such things, where one alternately plunges a part being tested into hot oil then liquid nitrogen. If tempcos are not well matched, the part deconstructs itself. This is a very severe test, but is a good predictor of future failure rate. Especially in power electronics.
Joe Gwinn
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I've a little bit of experience with HAST, but nothing as severe as what you describe. Military stuff is always pushing the limits.
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The brass part could be changed. Bronze, TeCu, BeCu if any might be better?
An Al puck in an oversized hole is an interesting idea. I assume the solder will shrink less than the Al, Do I want the puck to be pulled from the sides as well as the face?
George H.
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It IS possible, but you have to use something to scratch through the oxide coat first to bare aluminum. Usual practice is to puddle the solder on the aluminum and use a stainless brush through the molten solder until the surface is tinned, then sweat the other piece to it. My Alcoa book suggests that the high zinc-content solders work the best, another one recommends almost pure tin, go figure. Fluxes usually have some really active content to dissolve the aluminum oxide and will result in severe corrosion if not removed/neutralized.
If there's significant stress and it's a butt joint, you may have cracking and joint failure. In that case you might need some redesign, like going to solder tabs on your plates and maybe a thin aluminum shrink-fit tube over your brass to solder to.
Stan
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On Fri, 29 Jun 2012 19:15:13 -0700 (PDT), George Herold

Greetings George, What Stan says about scratching the surface through the solder is right on. You can solder without any flux at all. I have used the aluminum solders available at the hardware store and the strength is remarkable. You can buy little stainless brushes that are about the size of a toothbrush at the hardware store too. Once the surface is tinned it is easy to solder to anything else. If it was me I would avoid the use of flux on the aluminum just for ease of cleaning. Once the solder is molten and you start scratching the aluminum through the solder you will see that the solder will follow the brush as the brush moves beyond the area initially covered with solder. Eric
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On Sat, 30 Jun 2012 09:10:21 -0700, snipped-for-privacy@whidbey.com wrote:

Another trick is to sand the aluminum clean and OIL it, then solder. Vegatable oil, kerosine, WD-40, or motor oil will all work. do the final cleaning/sandong/wire-brushing through the oil and it can't oxidize so the solder tins the aluminum very easily. After it is tinned you can solder anything to it.
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On Sat, 30 Jun 2012 21:15:57 -0400, snipped-for-privacy@snyder.on.ca wrote:

I tried for the first time recently some tinning flux for plumbing. This is the flux that has the finely ground nonleaded silver bearing solder mixed with the flux. It worked very well for a non plumbing job soldering manganese bronze. I'm gonna try it today on aluminum with the wire brush trick, like the oil trick above. I'll post the results here. Eric
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On Jun 30, 9:15 pm, snipped-for-privacy@snyder.on.ca wrote:

Interesting idea, Thanks
George H.
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On Jun 30, 12:10 pm, snipped-for-privacy@whidbey.com wrote:

Thanks Eric that sound promising.
George H.
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On Mon, 2 Jul 2012 06:29:56 -0700 (PDT), George Herold

You're welcome. I hope it helps.
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The specialty rods marketed for repairing and/or joining aluminum parts will also work well with most non-ferrous metals.. which would include joining aluminum to many other alloys.
One can expect considerably more joint strength when using the aluminum repair rods, than the strength from using lead-type soft solder.
When the workpiece(s) can tolerate the higher sustained temperature of about 750 degrees F to join them, the aluminum repair rod will typically yield very strong joints.
--
WB
.........


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wrote:

Yeah, I figured I'd tin both sides and then mash 'em together.. (not sure exactly how to do the mashing, from center out at least.)
I never thought (or heard) of brushing it while under the solder, Thanks!

Yeah.. been there with some SS fluxes. Should be fine if I can tin it all nicely.

Well if solder doesn't work, then maybe some Al 'loaded' epoxy will, 'be the ticket'.

Thanks again Stan,
George H.
Since gluing is a possibility then there are a lot of other options. First, a press fit plug would probably be the best. If you want to solder, I wouldn't dick around with the zinc stuff. Get some La-Co Aluminum flux. This is for lead/tin solders. Scrape the aluminum clean and apply the flux (I usually scrape some more under cover of the flux) then tin the aluminum with regular plumbers solder. Tin the brass with whatever flux you prefer. Then clean both parts, apply regular flux and sweat them together. Practice with the La-Co on some scrap until you get your technique down.
If you want to glue, epoxy is a pain to bond with AL. The best stuff is an 2 part acrylic from Lord #406/16. This is the stuff they glue airplanes together with. You need a special dispenser gun and the first use is pretty spendy, but if you ever get a chance to try it you will be amazed at how well it works.
Paul K. Dickman
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wrote:
<snip previuos stuff>

Hi Paul, I need a good 'acoustic' joint between the two materials. I can see a press fit giving good contact around the perimeter, but I don't know about the two faces. What (I think*) I want is to get rid of all the air gaps at the boundary. I've been using this ultra sonic 'goop' between the layers, the quality of the coupling depends on squezzing hard and having the absolute minimum of 'goop'.

OK, that looks like an option. I'll order some. (I already committed to dicking around with the zinc stuff... can't just let it go to waste.)

Hmm, did you mean Lord 406/19. There's a lot of that on the web.
Here I was thinking that gluing would be the easy alternative, but the advice I'm recieveing seems to suggest that it may be harder than I thought.
Thanks for the wisdom.. at the moment I'll keep the Lord stuff as a back up plan, (If all the more commone epoxies we have laying around fail.)
George H.
*I've just started with this acoustic 'gizmo' so....

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On Fri, 29 Jun 2012 05:48:18 -0700, George Herold wrote:

Famously, Al quickly acquires a tough oxide layer of Al2O3 in air, and nothing solders to that. There are ultrasonic iron tips that break up the oxide so quickly and thoroughly that it can't reform before the solder gets to it, but they are too rare and pricey.
I actually had success with the method I heard about here long time ago: cover up your soldered area with light oil (engine/turbine) and scratch the aluminum surface vigorously under the oil with steel brush or a scraper, then apply hot iron loaded with solder. I used regular SnPb.
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