Problem Soldering Aluminum

[gilrussell]

I am dealing with an aluminum boat that has been dragged over the rocks and loading ramps too often, resulting in leaks at the stern. My solution was to solder (low temp) aluminum angle cut to about 6" pieces, covering the molded ridges (on the bottom). (The grooves on the top side have been patched by the former owner with JB Weld--it works but doesn' prevent the bottom of the boat from further degredation.)
But I couldn't get the aluminum to accept the solder. I cleaned it very well and then wiped everything with acetone. Then used acid flux, first liquid and secondly flux paste. I heated the piece on the opposite side from where I wanted the solder to flow. (I wanted to tin both the angle iron and the boat, then put it together and add some solder.) I tried it first with propane and then with mapp. The angle iron is probably three times thicker than the boat.
Where did I go wrong?
Thank you!

 

[gorilla]

What kind of solder were you using?

 

[djjsr]

I think there's special flux for aluminum.

 

[mzahn]

I think there's special flux for aluminum.

Put some small pieces of galvanized iron in muratic acid (don't breath the fumes) and prep the solder area with the cut acid. It worked 25 years ago for me.

 

[NASTYZEN]

I have used Aladin products before, with good resaults. Soldering Alu.can be quite difficult. Prep. is everything.
You could even have a rep. come over to help you out. These guys are good and have great products.

 

[ZRX61]

Why wouldn't you just attach them with PRC?

 

[gilrussell]

I was using old solder, just marked as "solder". Have used it on copper and steel and it worked fine.

 

[NASTYZEN]

I was using old solder, just marked as "solder". Have used it on copper and steel and it worked fine.

There's your problem right there! You need to use ALUMINUM solder AND flux or it'll never stick.....using lead.

 

[Bondo]

I was using old solder, just marked as "solder". Have used it on copper and steel and it worked fine.

Ayuh,...As noted, Solder don't/ won't stick to aluminum....

 

[rlitman]

Solder don't/ won't stick to aluminum....

It can be made to with the right flux, but I would sooner attach the pieces with JB-Weld and a few aluminum rivets than solder them if welding wasn't an option.

 

[trainer]

I'd just take it to a welding shop. They could probably weld it up quicker
, stronger, and for less money than what you would spend on supplies to solder it.

 

[Bondo]

Originally Posted by Bondo
Solder don't/ won't stick to aluminum....

It can be made to with the right flux, but I would sooner attach the pieces with JB-Weld and a few aluminum rivets than solder them if welding wasn't an option.

Ayuh,.... Plumber's solder will NOT stick to aluminum....

regardless what flux is used....

 

[rlitman]

Ayuh,.... Plumber's solder will NOT stick to aluminum....regardless what flux is used....

Again, that depends. Modern day solder is lead free. Today's lead free tin/antimony plumber's solder will not stick to aluminum. There are some solders that are made for aluminum (they're high in zinc content), but old 50/50 lead solder can be made to work with aluminum, but not acid core. Just plain 50/50 solid core (a staple of plumbers in years past), plus a liquid acid flux. Still, it requires patience, serious cleaning, and very careful heat control, and the best results are not spectacularly strong. JB-Weld has about the same bond strength.

Finding someone to weld it IS the best answer. Going with one of the "miracle" aluminum soldering rods may be a good second best. A glued and riveted patch may not be as good, but it will still probably outlast the boat.

 

[NASTYZEN]

Anyone can say anything, but this works best.

http://www.aladdin3in1.com/products/solder/low-melt.php

I've used it on Alu. rads and inter coolers with great results before. Nothing else I've tried even came close.
There used to be Harri Kirri, but I can't find them any more.

 

[Tom_20m]

Tractor supply and even harbor freight have those low temp (700 degrees F) aluminum brazing rods. I've used them on my john boat and they work. You just need to take your time, prep, the area and whatever you do, don't heat and melt the rod. Heat the area and than scratch the rods on the area to be repaired and build it up. 2nd option is a torch with aluminum welding wire. There's a gentleman on Youtube who has a video of him brazing two aluminum pieces together and then testing the sheet out. Very informative video.

 

[ptschram]

Anyone can say anything, but this works best.

http://www.aladdin3in1.com/products/solder/low-melt.php

I've used it on Alu. rads and inter coolers with great results before. Nothing else I've tried even came close.
There used to be Harri Kirri, but I can't find them any more.

This!

Use a NEW, CLEAN stainless steel wire brush to clean the surface.

Once you get the hang of it, it's as easy as silver solder, soft solder, brazing, etc.

Remember, the solder goes where the heat is.