Soldering Aluminum to aluminum

I'm building an aluminum bridge for my railroad.  I need to solder the side braces rather than using screws and nuts.  I've ordered a 150 watt chisel soldering iron and need to know what items (solder etc) I need to perform this project.  Any assistance greatly appreciated.  I would rather not use a torch on this project unless absolutely necessary.

Picture of Soldering Aluminum to aluminum

If I need to solder aluminium then I make use of two options:
1. Normal works that won't require too much in terms of structural integrety.
Plumbing solder is used here.
Aluminium is cleaned in the area of the joint, then heated from the other side using a flame.
Once hot enough so the solder would melt on the surface I use a stainless steel wire brush to clean again and a stainless steel needle to keep scratching.
Even with just a tiny amount of solder on the surface you can then "wet" the are until an even coat of solder is done on the area.
After that it is normal soldering from here on.
2. Heavy duty works.
Here I use aluminium brazing or welding rods from the hardware store.
Principle is same as above just that I use the rod directly for the scratching action and only assist with needle and brush.
Tricky bit is that these rods are just a few degrees under the melting point of aluminium, so it takes care not to overheat the material.

Whatever you do: never use a solder with a flux in it.

Yonatan2413 days ago

I think brazing aluminum works better https://www.instructables.com/id/How-to-Weld-Alumi...

Been over to read the brazing aluminium reference and it is quite interesting especially the comments. From them, my favourite would be some sort of superglue rather than brazing or soldering.

TCSC4713 days ago

I have successfully soldered copper wire on to aluminium chassis. The secret is to drop some thin lubricating oil on to the aluminium and then, under the oil, scratch away the surface oxide layer of the aluminium with a screwdriver. The purpose of the oil is to stop the aluminium surface re-oxidising, which it would do quite quickly if exposed to air. Don't clean away the oil but just apply your iron and normal multicore solder to the aluminium and you should find that the solder runs quite happily onto the aluminium if you can get it hot enough.

You are correct in thinking a high power iron would be helpful but I managed it with a 25 W iron as I only had to join small areas.

I learnt this trick 55 years ago on my apprenticeship but have never really found a use for it in my work.