O / A welding Alum.

I have done a little O/A welding of aluminium using a flux cored rod. I used a very soft flame with very low pressures on the regulators, I seem to recall about 2 psi on both. I cleaned using a stainless steel brush, and I used a slightly reducing flame (less oxygen than neutral) to avoid any oxidization from the flame.

If you are using 16 Ga aluminium, this will be pretty hard for a first timer - I used 1/8" thick material for my project and found that to be a lot easier to control. the problem, obviously, is heat control. It may help to start your puddle with a blob of rod rather than trying to get a puddle started in the aluminium before adding rod.

The point, I guess, is that this can be done by a newbie like me, but it's hard. Don't start on your finish pieces...

Brian

Kent White at TM Technologies seems to be a guru in O-A welding of aluminum. I've seen him weld at demonstrations at the EAA airshow in Oshosh. He makes it look easy, but he will say it takes practice...practice...practice. He sells equipment, fillers, and video's. In the real world he makes custom aluminum sheetmetal parts for cars and aircraft. This is not the aluminum brazing/soldering that hawkers in the flymarket call "welding aluminum". So plan on spending time and money.

Al oxidises VERY quickly. The coating it develops makes it very difficult to weld....

If using an Oxy Acetelene set you will need a very soft carbourising flame, by this I mean use low pressure, a large tip size and have an excess of acetelene in the flame. This tends to minimise the oxidization. You will need to be able to supply a lot of heat input quickly, as the Al conducts heat very well.

Make sure your work is spotlessly clean.... do NOT use a normal steel wire brush... get a stainless steel one! The use of a steel wire brush will leave you with weakened welds as it contaminates the Al while you are trying to clean it. Brush the area to be welded just before commencing the weld! This is to remove the oxide skin (which forms IMMEDIATLY! and gets thicker and thicker the longer you leave it!)

Flux.... Soduim Flouride is what I have used. Should be available from most good welding supply stores. Apply it in a similar way you would use brazing flux. Gently heat the welding rod and dip it into the powder to get a coating onto it (unless you can purchase coated welding wire). Preheat the joint area, and apply flux poder to this area too.

Welding... It is DIFFERENT welding Al compared to steel. You need to 'dip' the molten end of the rod INTO the weld puddle. Failure to dip the rod will just leave you with a surface that is covered in lumpy bits of Al that are not really joined into the parent metal, they are held in place with the flux. The reason for needing to dip the rod is the oxide formation, which speeds up as you apply heat! The oxide stops the Al from the rod mixing with the pool of molten metal on the work. Dipping the rod breaks this surface skin.

I got taught how to weld Al with an Oxy Acetelene torch about 25 years ago by an old farmer, who was also a qualified boilermaker. He ran a farm machinery repair business on the side to supplement his income, as well as teaching welding in night classes. I didn't think it could be done with the Oxy torch until then!

I have found I can weld Al that is about 2mm thick.... any thinner and it just turns to mush as soon as I heat it. Thicker Al is easier to weld, but requires pre-heating to a larger degree, and if there is too much heat being sucked away from the weld area by conduction you may even need to use a helper with a second torch to provide a constant pre-heat to the area surrounding the weld to enable you to get enough heat into the joint.

A final word of warning..... it is a balancing act between having too little heat, and not getting a good joint, and having too much heat and ending up with a pool of molten Al falling to the floor leaving a huge hole in the work. Pre heat the general area well.... then after fluxing confine your heat to the fillet (joint) area, you need to be able to supply heaps of heat quickly compared to welding steel!

Pip

Guys Thanks for all your help. I feel I have a lot of test runs to do. Thank god for scraps. Pippa, I am glad you said to use a large tip, I was going to try it with a small tip low heat.

Thanks again, more play time trying new things

Don

YES!!

Long before I got my TIG, I learned to O/A weld Al. I picked up Al frame folding garden chairs that were broken or cracked in the corners. I made sheet metal gussets and welded them into the corners. If I screwed up, I returned the disaster to from whence it came. Once I got the hang of it (it took more than a few) I wound up with quite a good collection of chairs that were better than new (still have a dozen or so) and the skill to weld Al.

But TIG is far more fun! :-)

Ted

The only thing I can add to what others have posted is to put a support piece under the weld. Aluminium is "hot short", i.e. has no strength when it is hot/molten. So, as you might put a plate under sheet metal, it is also a good idea to put something under Al when O/A welding

Flux, rod and special filters. The real problem with AL is keeping the flux out of the weld as it keeps corroding.

Al doesn't change colour as it heats up.

On thicker slabs, a trick is to coat the piece with carbon (acetylene) flame until black then heat until all burnt off and it then has sufficent preheat.