Question on aluminum soldering

[BlueOcean]

I am building model sailing and power yachts using the bread and butter method with mahogany, basswood and Spanish cedar. I've developed some unique rigging using a variety of materials from hardware, fishing, jewelry making and sail making. I intended to use 1/8" aluminum tubing for bow and stern pulpits and rails but i have been unsuccessful in joining the tubing. I've tried soldering, but the aluminum tube melts before the solder and when the solder I have did melt it did not adhere to the aluminum. I've tried a dozen glues. None worked. I've even tried lashing the pieces together using very thin jewelry wire but it's a pain and the result is not acceptable. Supposedly aluminum can be soldered and I remain bullish on that method but I need some guidance. What solder/flux do I need? Any special prep to ensure a good clean joint? What tool is best for this type of soldering? Where can I get the materials at a reasonable price? Is there a technique for holding these small pieces while soldering them? Please let me know how I can do this or, if you have a better idea I am open to learning. Thank you. BlueOcean

[mtaylor]

Are you using a solder designed for aluminum?  Also, you'll need a low power soldering tool.  If no one gives you and answer, do some Googling for aluminum solder and soldering tools.   I did solder aluminum some decades using a small torch and aluminum solder to make spoiler for a car.   If I recall correctly, you're actually welding the aluminum.

[Dr PR]

Brass is much easier to work with than aluminum! It is easy to solder and machine.

 

If you want a "silvery" metallic look you can always use a relatively inexpensive electroplating kit to put chrome or nickle plating over the brass.

 

Note: I have never used the electroplating method, so I don't know what effect tin/lead solder will have. The plating instructions say it works on tin and brass, but I don't know how well it will work on areas where the tin/lead solder has dissolved into the brass (soldering works in part because the tin dissolves into the brass).

[No Idea]

Hi Blue Ocean - If you need Aluminium soldering I've not yet seen a decent solution.  I'm an ex coded welder and if I needed Ali joining I'd pop into my local welders and ask them to TIG weld it for me.  It takes them seconds to do our sort of job and my local shop would do it for the price of a pint of beer.  

[Roger Pellett]

There are several ideas that you can adapt from full sized pipe welding technology:

 

1. Socket welding-  In this technique a smaller diameter pipe is slipped into a larger diameter fitting with the joint secured by a fillet weld between the pipe and fitting.

 

2. Backing ring- When making a butt joint between two pipes of the same diameter a smaller od ring bridges the gap between the two and acts as a dam to support the liquid weld metal fastening the two pipe ends together.

 

3. Pre-Deposited weld metal- Here, a ring of weld metal is placed between two pipe ends to be joined.  The ring is then fused and weld metal can be deposited over it to complete the joint.

 

Aluminum readily forms an oxide film when heated that prevents deposited weld metal from adhering. For this reason, it is usually welded with an inert gas shielded torch.  Therefore, trying to solder it with an ordinary propane or butane torch will not work.  It also needs to be clean.  There is an old story about welding the first aluminum boats.  When welds continued to fail, two pieces of cleaned plate were set up in a clean room and the welder was observed through a window.  He picked up his welding torch, flipped his hood down, and from long habit ran his gloved hand down the weld prep groove to sweep out foreign material, thus contaminating the joint!

 

Aluminum melts at about 1200F so any soldering material must melt at a temperature below that.

 

I would mechanically clean the joint to remove anodizing  and oxide film, degrease with acetone and assuming the correct aluminum soldering material solder with an electric iron.  It would also seem important to somehow prevent the material from oxidizing after cleaning and before soldering.

 

A more promising technique might be to use the backing ring/socket weld technique above and epoxy, since small diameter Aluminum tubing is available in telescoping sizes.  Cut a short piece of the smaller tune, slip it into the larger so it protrudes a short distance, secure with a dab of epoxy, and slip the end of the other piece to be joined over the protrusion, secured with epoxy.  For a “branch weld” drill a hole equal to the diameter of the smaller tube in the side of the run, slip the protruding smaller tube end of the branch end in and secure with epoxy.  I believe that you should be able to easily find Aluminum filled epoxy.  The brand JB weld comes to mind.

 

Roger

 

 

 

 

[kurtvd19]

With the difficulties of soldering/welding aluminum why not just use brass rod.  It's easy to bend to shape and can be soldered easily.  The photos show brass rod bent to shape and soldered together (the kit provided aluminum tube that was to be glued together).  The brass rod can be plated or painted.  Krylon makes a spray chrome paint -Premium Metallic Original Chrome that was decanted from the can and then airbrushed onto the parts in the photos.  Stay-Brite solder was used with resistance soldering with the parts on the model - the perfect jig - the resistance soldering doesn't transmit enough heat to affect the model.  The parts were removed from the model, painted and reattached to the model after the hull was painted.

 

 

[grsjax]

Haven't tried this yet but it looks good.  https://www.amazon.com/KappAloy9-Aluminum-Solder-diameter-medium/dp/B00HYKQ6XY?ref_=fsclp_pl_dp_3

[BlueOcean]

To all who replied to me with your insights, suggestions and guidance all I can say is WOW and thank you. (Since I posted this cry for help I did visit my local welding supplier, found some solder that was supposed to work on aluminum (and didn't despite cleaning and flux, but maybe I did not do a good enough cleaning job) and tried some epoxy that was supposed to work on metal (aluminum) - it didn't.) There were several good ideas for how to do what I want'/need to do and I am going to try again to "solder" the aluminum tubing I have using some better materials and techniques suggested. And if that doesn't work I'l try using brass rod. That looked like a good alternative. Again, thank you to everyone for your thoughtful replies.

 

BlueOcean

[liteflight]

Aluminium can be soldered readily using An ultrasonic soldering iron and the appropriate solder.  The snagette of course is getting hold of a u/s iron.  The solder is specifically for u/s soldering as well.  It’s basically normal solder with additions to allow it to bond to the metal surface.

 

I used to use u/s soldering to join copper to graphite(!) and it would also solder anything happily to glass, ceramics, etc.  you could regard the u/s vibrations as abrading the surface enough to get the solder to adhere to the base material

https://en.m.wikipedia.org/wiki/Ultrasonic_soldering
 

There are other techniques to solder aluminium, but all require technique and practice, and I doubt if they would give you the result you want.