Sciencemadness Discussion Board

aluminium welding

jimwig - 5-7-2005 at 17:19

at certain events such as gun shows and county fairs there has been in the past folks who demonstrate a kind of alloy which will solder/weld aluminum. does anyone have knowledge of the alloy's composition?

oh i should add this is done with heat of a propane torch

jim

E.b.C.:Title

[Edited on 9-7-2005 by chemoleo]

12AX7 - 5-7-2005 at 22:04

Not weld, braze (or solder). The former is a ZA alloy (zinc aluminum) with melting point 716°F (eutectic) up to about 900°F. The latter is a tin-zinc solder.

The brazing rods can be used without flux, in which case the (solid) rod is rubbed against the work, mechanically removing the aluminum oxide surface. Solders usually come with some sort of chloride + fluoride flux that's probably very bad to eat.

Tim

jimwig - 8-7-2005 at 13:39

is this within the range of preparation of the average noob type with access to moderately high temp via muffle furnace say like 2000 degrees?

that is can the zinc and aluminum be alloyed in a simple proces and extruded (whatever) to form usable solder brazing material.

i remember the demonstrator defiantly stressed the important of oxide removal via staninless wire brush. this is i understand the largest impetiment to successful aluminum brazing/soldering.

uber luminal - 8-7-2005 at 15:09

Those people that sell that solder are not very smart if they say you must use a brush to remove oxides from the Aluminum.

Coming from someone who makes a lot of custom alloys, its almost cheaper to buy the crappy solder than to try and make it. You must get the mostly pure raw materials (which costs money to buy and ship esp in low quantities). Then you must spend time prepping and massing out the materials. put them into some sort of furnace that will not allow oxidation. (gas with flux, muffle with vacuum or sealed can etc). bring it up to the alloy temp, which is pretty low(below 600C), allow it to sit, and then somehow quench it, without contaminating it again. Then to extrude the stuff... no... thats a lot of work. I would swage it if it doesnt end up brittle.

12AX7 - 8-7-2005 at 16:01

Erm...

No offense but you really don't have much really practical experience with metal, do you? Brazing isn't exactly analytical chemistry.

Aluminum scrap (besides cast alloy) and zinc scrap (any) can be mixed to get some sort of a ZA alloy, around 5-10% Al I'd figure for a brazing rod. Heat it to a dark red glow (at night might be helpful) and cast a long thin ingot in a (possibly preheated) ingot mold. You can also pour into a sand mold with holes poked in it of the desired size.

For the Zn-Sn alloy, you might get away with some OTS lead-free solder. I'd have to guess you'd want one of the sort that contains copper and/or silver to harden the tin, as opposed to antimony, although depending on how much Sb it has, it may still be acceptable when alloyed with zinc.

Tim

off topic

uber luminal - 9-7-2005 at 15:32

Quote:
Erm...

No offense but you really don't have much really practical experience with metal, do you? Brazing isn't exactly analytical chemistry.
ohh harsh. I am curious what leads you to believe that I 'really don't have much really' practical experience with metal' ? (in your expert opinion of course. )

I also would like to know why it is suggested to scratch the surface of the Al... to remove the Al oxide...

scratching the surface with something that is harder than the Al is useful to create mechanical sites for the liquid metal. (and to clean it). Scratching the surface with brazing rod... which is likely softer than the base alloy, helps the braze or solder adhere to the surface. However, neither of these two methods, would be methods for removing surface oxides for any period of time that would be of use.

12AX7 - 9-7-2005 at 16:39

Quote:
Originally posted by uber luminal
ohh harsh. I am curious what leads you to believe that I 'really don't have much really' practical experience with metal' ? (in your expert opinion of course. )


Well in particular... no one in the business cares about 99.99% pure materials (except for sulfur in ferrous alloys, but that's a special case). I get passable results (yeah, for overbuilt castings ;) ) using literally any aluminum available.

Tolerances get comfortably baggy and loose when you're not doing things to litigious specifications...
Quote:
I also would like to know why it is suggested to scratch the surface of the Al... to remove the Al oxide...

scratching the surface with something that is harder than the Al is useful to create mechanical sites for the liquid metal. (and to clean it). Scratching the surface with brazing rod... which is likely softer than the base alloy, helps the braze or solder adhere to the surface. However, neither of these two methods, would be methods for removing surface oxides for any period of time that would be of use.


Well, then, I guess you'll just have to see it to believe it.

I've done it with 2.5% Cu, 97% Zn (oh I'm sorry, Cu0.025 Zn0.97, as bulky as THAT is...), when it gets to the right temperature, the oxide losens from the metal and, more importantly, the rod forms an eutectic which melts on contact. This lubricates and makes the oxide that much more mobile, allowing it to be simply pushed aside. Without pretinning or fluxes, full penetration cannot be had, although with careful temperature control and technique, smooth fillets can be made.

Tim

P.S. Yes indeedy, this (and the preceeding) post of mine have been unusually harsh... just trying things the MSDB way... er, oops...

Aluminium solder

Lambda - 9-7-2005 at 18:28

Aluminium solder # 1

Aluminium....30 parts
Zink................20 parts
Tin..................15 parts
Copper.............5 parts
Bismuth..........10 parts
Silver...............10 parts

Aluminium solder # 2

Aluminium......88 parts
Silicium...........12 parts

Remark about unit usage:
Parts = Weight units.

Refference:
UPLOAD / LAMBDA / Mengen en Roeren (Dutch) / Mengen en Roeren volume 1.
Page: 225.

Location:
MadHatter's FTP (Mengen en Roeren volume 1 & 2).

Book downloaded from Gamekeeper's website:
http://gamekeeper.deds.nl/

Remark: No specific flux for Aluminium was found in "Mengen en Roeren" volume 1 & 2. These fluxes are cheap, and easily obtainable. Fluorides may be the stumbling block in making it yourself.

[Edited on 10-7-2005 by Lambda]

jimwig - 10-7-2005 at 17:56

girls girls didn't mean to start a pissing contest. although that is an interesting graphic.

no, i may be wrong but surface oxidation can be removed with a wire brush or at least enough of it to allow some type of soldering/brazing (try not to nitpick my choice of words here).

'course an approipriate flux also helps.

i have been doing that for a while. you do not have to be a metalagist (sp?) to understand this rather basic operation.

oxidation layers for the most part are surfical. and since aluminum oxidizes almost immediately then removing the top most surface should reduce if not remove the "rust".

i suppose this affinity for aluminu for oxygen has to with bond angles, valence coordinates and all kinds of stuff that i really don't care about.

you see i don't have refine my own petroleum to use it my infernal combustion engine.



thanks for the help ----

[Edited on 11-7-2005 by jimwig]