Guess I could but I don't think it is thick enough to give a good hold

 

you can not weld a steel nut to alum tree, your going to need a converter wire feed spool for your mig to weld alum anyway. I know the one for my lincon was $$$$, best way to do alum is tig, also the nut is chrome so you will have to grind the chrome off to get to the bare metal to weld the steel, but again this is pointless as you can not weld the two opposing metals together, if you where to weld steel to steel your going to want a shielding gas as well so you do not get a ton of splatter on my mig i run a 80% Argon, 20% CO2 shielding gas in my mig and strait CO2 for when i really need to throw alot of heat into a part, we also do a ton of mig welding in the shop on alum, stainless, steel, you name it. to add a nut to the tree you can also just drill a hole, tap it, then run some threaded rod down it, little red loctite and then put on your nut, i would go this way anyway, much cleaner.

 

pretty sure that the tree you posted there is steel... but again that is chrome and the nut is chrome so that will both have to be ground off andd then welded, or you will not get penatration or a good hold. PLus the heat is going to blue the metal, so you will want a cold compress on the back side and ready for the top to reduce heat transfer, but again i would not do this, just drill a hole, and run a bolt up from the bottom, you can always grind the head down for clearance issues

 

why not drill and tap ?

 

Joe's on the right track ... The lower tree is steel. If the Nacelle will cover the tree after installation, the chrome shouldn't/wouldn't be a factor. Once welded, just cover the area with some Rustoleum Chrome or Silver paint ( or send it Joe! ) and finish the project. Otherwise send it out to be re-plated ( by a reputable plater, of course )

 

I took a magnet to the lower tree and it stuck so guessing steel, I would have to grind off the chrome and then weld a steel nut, everything will be covered by the Shovel head headlight nacelle so bluing or discoloration is not an issue.

 

Drill a hole and double nut it, nut on top and nut below

 

I wouldn't think its steel, its probably an alloy. The magnet may stick to it but that doesn't prove anything but the fact it has iron in it. It is possibly to weld different metals together but its not easy and impossible to get any strength with your basic mig. Just drill it and put a bolt through it any you will be sure it will not brake or wreck the chrome. Taping alloy can be done carefully but the threads will be weak because the hole was not there when the part was cast.

 

Joe is probably the most knowledgeable when it comes to this kind of thing and has probably provided the best advice.

 

if you flip the bottom tree over you will see the weld on the stem to the tree , I welded on a 1996 heritage lower tree last year , its still holding and was not a big deal . I would not weld on nut but a piece of cold rolled ground to round shape of tree or use a half round file to get saddle shape in cold roll , clean chrome off use a c clamp to hold cold roll in place then tack cold roll on top and bottom of tree and weld then drill and tap thru cold roll and tree . DO NOT TRY AND COOL METAL AROUND WELD , if you put wet cloth or quench metal you will harden it and it will be harder to drill and tap and you could make it brittle so let it cool on its own