Scratching my bald head

[Cedge]

I've always been told that one can't solder aluminum. That has always been one of those unquestioned facts that "everyone knew".

The links in another thread that lead to out of copyright books have consumed more than a few hours of late and one of those old texts describes how to solder the stuff with old fashioned lead/tin solder.

Aluminum oxide is formed as soon as freshly cut aluminum is exposed to air. Aluminum oxide is what forms sapphire and ruby. both are next to diamond on the hardness scale and prevents solder from forming a bond. That all makes sense, so how does one get past the barrier?

The book describes applying the solder with a copper iron and while it is still hot and plenty of flux is still there, brush the intended joint with a wire brush to break up the oxide coating. Apparently the flux gets beneath the coating, erodes it and the molten solder prevents air from reforming the oxides.. The solder then binds with the bare metal and the joint forms a solid bond.

I've not tried it yet, but I think I'm going to have to give it a go, just for the curiosity factor. You could really mess with some minds if it actually works.... not to mention expanding the number of places aluminum can be used effectively.

Anyone here ever had any experience with this "lost" tidbit of information? I also wonder if it would stand up to silver soldering, which came into use many years after the text was written.

Steve

 

[Bogstandard]

Hi Steve,
I did a few experiments in soft soldering aluminium in the late sixties, what a pig of a job. Had a bit of success but the joints were very weak. But that was using the fluxes that were available then.
You can get very aggressive fluxes nowadays that easily allow you to solder aluminium using commercially made solder sticks, and supposedly the joints are as good as the parent metal. The best vid I saw was a chap repairing a hole in the bottom of an aluminium drinks can.
I think you might hit a few problems with silver soldering because of the heat involved, the oxide layer will form just too quickly for standard fluxes to work.

John

 

[Cedge]

John
I've seen the guys hawking aluminum "repair" rods for years, around the local flea markets (boot sales) but that appears to be an aluminum version of brazing. It would take a gentle touch with a torch to do something as thin as a coke can, but they do it every weekend for hours on end. It just surprised me after all these years to read that it could be soldered.

A bit of Googling does bring up several techniques using today's available materials, but one readily admits the options are fewer since lead solders are no longer an acceptable blend. I'll have to give it a shot now that I've been exposed...LOL.

Most people think aluminum can't be plated, but all the custom motorcycle builders here in the US do it on a regular basis. A coating of zinc is applied and then nickel can be applied, followed by chrome. Copper can be applied over the zinc to form a surface that can be buffed to a high shine, while eliminating deep scratches. The copper works like a " filler primer" as it is built up enough to withstand buffing without exposing the aluminum base metal..

Steve

 

[Bogstandard]

Steve,
You love raking up my past.
Your bit on chroming ally reminds me of the time we customised one of those old american tractor engines, sorry harley engine (same thing)(wait for the sparks to fly now).
We had all the bottom end polished up and very deep hand engraving, then we smuggled it into Rolls-Royce motors (where I worked at the time) and had it fully plated up. It made the engine look almost useable.
I wish you success with your soldering experiments, keep us posted how you get on or not.

John

 

[1Kenny]

Steve,
I think I have one of those rods some where in the shop that they use on the beer cans. Haven't used it be it would seem to be better than JB weld. My local welder said he would have to whip me if I used it.

The chrome shop I use chromes aluminum. They polish it bright first, acid clean then copper coat it. Polish the copper coat bright then acid clean then another coat of copper coat and polish. That insures the chromic acid wont get to the aluminum. Then they acid clean and chrome the part. He has told me the extra layer of copper makes sure the chromic acid won't get to the aluminum so it won't pit or flake over time. It seems to be true.

John,

Here is a couple of tractor engines I have done with special carb to intake manifold adapters. lol

They run very well when the manifold pressure is raised 1 BAR.

 

[tattoomike68]

LOL tractor engines.

 

[Bogstandard]

Lovely bit of work there Kenny, it should be able to plough a bit deeper with that blower on it. :lol:

John

 

[rake60]

That is an interesting topic Steve.
I've seen aluminum brazed and Mig welded, but I've never seen it
soldered. The American Welding Society says it can be done and
goes into detail on the subject on their page:
Tips for Soldering Aluminum
I'll have to try it here. I can think of many places it could be useful
if it works.

Rick

 

[Cedge]

Silly John...
We all know a blower ain't gonna do no plowing... you move leaves around the yard with it. You some kinda city boy?....LOL

Rick...
I love finding out things like this. The same thought struck me when i read it. It has to have some uses that would come in handy once in a while. Those old publications have a number of lost tips in them.... some of which might have homeland security officers breathing down your neck, these days...LOL

I've been cleaning up and tweaking the arrangement in the shop today. It finally got so out of hand that I had to just stop and do the domestic thing. Pretty bad when the only one to complain to about lousy housekeeping is yourself...LOL. I think 50% of my hand tools were out on one bench or another, but damned if I can't find anything I need now. I won't know how to act.

Steve

 

[macona]

Harris makes a solder called Alumasolder. Comes in a little plastic container with a bottle of its flux.

Works good. I have used it to solder the aluminum and steel tabs on lithium ion batteries together.

Heres another interesting thing...

Did you know you can solder glass?

 

[Tin Falcon]

I've seen the guys hawking aluminum "repair" rods for years, around the local flea markets (boot sales) but that appears to be an aluminum version of brazing. It would take a gentle touch with a torch to do something as thin as a coke can, but they do it every weekend for hours on end. It just surprised me after all these years to read that it could be soldered.

Steve:
Somewhere around here I have some of that rod. the guy that demoed it showed that the base metal was actually penetrated. The sign of a true weld. I asked him how do I know that it is a true weld and not just solder . He started a bead and then poured off the molten metal shure enough some of the base metal was melted away. the trick is you have to clean off the oxidation inside the molten pool with a piece of S/S welding rod . so it is almost three hand welding one for the torch one for filler and one for the cleaning rod .
Can not say I have really used it I did some experimentation many years ago. I guess like any other welding a good eye and lots of practice to get good.
The stuff was not cheap IIRC 20 bucks a pound 20 plus years ago.

Tin

 

[Stan]

The aluminum rod sold at flea markets has been around since the 1930s when auto body shops used it to braze the fancy cast white metal grills in cars of that vintage.

There is definitely a knack to using it, but I have even brazed a leg on a aluminum ladder that has has been in use for about ten years since the repair.

 

[BobWarfield]

My welding teacher mentioned the wire brush trick, though he didn't actually demonstrate it. Got a Tig now, so that's not the approach I'd take, but it could be a lifesaver for someone that didn't. Even though its pretty straightforward to weld aluminum with the Tig, its still harder than welding steel. If I have to weld it, I tend to favor steel.

I like silver solder and brazing too for certain tasks.

Cheers,

BW