Tig weld Al 5005 to Magnesium casting

Date 04-26-2004 10:26

We have an interesting job at the moment where we have to weld some valve spring oiler tubes internally to some Dodge Viper race car valve covers.
The valve covers are of Magnesium die cast alloy and the oiler tubes are 5005 aluminium 1/4" tubing.
When welding the 2 materials together with a Magnesium alloy filler, the weld seems OK on the Magnesium side but I'm not so happy with the Mag filler to Aluminium tubing.
I tried a test piece on some Mag plate we had where I used the Mag filler as a buffer then tried using 5356 (5% Mag filler) to weld from the buffer to the tube with no success as it simply pulled apart very easily.
I'm getting better results with the Mag filler straight to the Alum tube but I'm still not quite happy so I was wondering if there is another filler wire which will act as a buffer from the Mag filler to the Alum tube.
Is there another Alum filler wire with a higher Mag content than 5356 5% Mag content? Or can anyone suggest another alternative?
Regards Andrew.

By brande

Date 05-08-2004 05:15

Knowing the exact mag alloy woud help.

Aluminum and mag really don't get along well when welding.There can be some serious metallurgical problems.

As far as I know-there are no RELIABLE buffer alloys.At least for welding.

My first thought (like yours) is to go to a hi mag content aluminum alloy.5356 and 5556 are the highest at 5.5% or thereabouts. No sense, usually, exceeding the alloy of the weaker material.

In this app, however, you are finding better results with a mag filler.

I would go to AZ61A, for it's ductility.

Watch your heat. Too much heat can sometimes look like impurities.
Mag can give the appearance of "boiling". If this happens, your heat is too high. Grind out as this will be a pourous weld. A couple of weld/grind cycles should give you the results you need.

Hope this helps

Good Luck

brande

By awill4wd (**)

Date 05-10-2004 10:39

Brande, thanks for your reply but I have since found out as you suggested that the two metals are basically incompatible.
I have been in touch with an importer of welding consumables who specialises in "exotic" materials and he told me that Magnesium is something of a "hermit" metal in that it prefers to be by itself. Apparently aluminium can be alloyed to it up to a maximum of about 8%-10% and no buffer metal is available unfortunately.
I had to tap a thread in some of the tubes I had welded in the valve covers with mag wire and they have now torn away from the valve cover. It looks like Araldite or Devcon may be this fabricators friend :-)
Regards Andrew.