Welding aluminised steel exhaust

[Bonnewagon]

I am helping the neighbor's kid get his car back on the road, thus freeing up their garage for the dad. I had to weld some 2.5" aluminised exhaust pipe to a thick CAT flange which I think was also aluminised. I normally gas weld anything exhaust related but this stuff was fighting me the whole way. It would not melt and flow like I expect regular steel to but I got a little better flow using some brazing flux you dip the rod into. I even went to a larger tip but that just blew the puddle around, and no matter how hot I got it, the two metals acted like they were afraid of each other. After it cooled down I looked at it and suspect it will pinhole leak. Any one have any tricks with this stuff, flux coated rods, special alloy rods, special flux, anything. Or maybe I should just start over and arc weld it?

 

[565bbchevy]

Did you grind any of the coating off prior to welding?

 

[Bonnewagon]

Yes, bare metal. You know how steel gets yellowish-white before it melts away? This gets reddish-orange then just bubbles.

 

[lightemup2]

yes your better off mig welding it (GMAW) using oxy argon mix

 

[pontiacgp]

muffler shops use mig welding on that stuff

 

[Bonnewagon]

I considered that but when I was inspecting the original welding I saw lots of MIG wire that had penetrated right through the pipe into the inside of the flange. I assumed that the aluminised pipe was thin and was easy to burn through with the MIG. The flange is very thick in comparison. Or maybe whoever did the job was using too much amperage and/or just a sloppy welder. That's why I decided to use gas as I usually have better results than arc on exhaust stuff. The piece is short so I think I will seal the end and test for leaks with water. If it leaks I guess I will break out the MIG and do it over again.

 

[lightemup2]

yea either of those could be the reason, more then likely they are using to much heat, if your wire feed and heat settings are right you should have no problem migging it... just remember to start your arc on the thick flange and push the puddle to the thin walled exhaust. and don't try to make a full weld around it, because it heats up quick, id do a 1/4-1/2 inch stitch weld on opposite sides of the pipe, to distribute the heat, and just do that till its fully welded, like you would do when putting a wheel on (star pattern) and once you do that inspect it let it cool then you could make a full weld around if need be, because now you will have a thick base to weld to and wont blow through right away like it would on the pipe itself... also don't do real slow, move your hand at a steady pace so you don't heat up one spot to long.... ( just some helpful tips)

 

[pontiacgp]

Mark, you probably already thought of this but can you expand the pipe to slide over the cat and put a clamp on it?

 

[Bonnewagon]

Thank's for the help guys. I water tested the job and of course it leaked at several spots. So here's what I did. Rather than cut it apart again, I saw that I could I could maybe put an arc bead around the INSIDE of the flange where the pipe poked through. Seeing how the brazing flux helped I grabbed my POS Harbor Freight stick welder and some Easy Strike flux coated rods and went around the inside of the flange. That worked as I did what Lightemup2 suggested and got the thick flange part molten first, then worked that over to the pipe. I did it in tiny bursts all around the perimeter until it was complete and looked good. Then I went back to the outside and redid the seam where the pieces met and any other spot that looked crummy. Now there is weld outside and inside so I doubt there will be any leaks. This flange is before the muffler so you know even a pinhole will be loud and aggravating. That's why I keep the HF welder, every now and then it is indispensable. Definitely the ticket for the aluminised pipe. PS-Steve, someone had cut the CAT off, flange and all, so I needed to restore that so it would pass emissions inspection.

 

[Blake442]

Glad you got it worked out, Mark.

I've had awesome results with Muffler Cement on any small leaks that can show up down the line.