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Up Topic Welding Industry / Technical Discussions / More casting ?s
- - By supermoto (***) Date 03-09-2011 11:55
I have been through 20 pages of this forum and I still can't get enough info.  There are some great articles and info, I guess just not what I need.

I would like to know more information on welding aluminum and magnesium or the combination of the two.  Info such as fillers, and GTAW polarity and any type of helpful hints.

I have tried it and was unsuccessful as I think the one I tried was magnesium.  Getting the area cleaned was most difficult and no matter what I did there was absolutely no fusion and all it did was pop.

Thanks in advance
Parent - - By Lawrence (*****) Date 03-09-2011 13:34
I was voluntold that I would be the "Mag" man for United Airlines back in the 1980's.  Spent a couple of years doing nothing but repairing Aluminum and Magnesium castings.

Both can be tricky...  Some older magnesium castings simply have too much residue/contamination right in the metal matrix to be weldable... You just keep routing until you hit clean metal or you scrap the project.. There are times when thats just how it rolls.

There are a couple of alloy families in the Magnesium group and fillers and pre/post heat operations are different for each..  So it's important to research and find out exactly what type of magnesium you are trying to repair.

There are also a couple of different techniques to repairing Mag castings... Including a very interesting DCRP/Helium combination for doing surfacing welds with reduced heat input.  (The only GTAW/DCRP operation I'm aware of).

Crack Repairs of Mag and Aluminum almost always require 100% removal of the crack. You will NEVER get away with routing partially.  Verification of crack removal with Dye Penetrant can save alot of rework.

Flanges and Mating surfaces are often metal sprayed. This must be removed if a bolt hole or alignment pin is removed and the hole refilled.

But rather than me babbling until I stumble upon what you want... How about you telling us more about your project..  Maybe something can be done.
Parent - - By supermoto (***) Date 03-09-2011 13:47
The one time I tried it was on a dirt bike and all I used was 5356 and a miller dynasty on AC with some pure tungsten.

I have been asked to do repair like this bit unable to do it properly. I would like to try with other techniques but my knowledge is limited to what to do.
Parent - - By Lawrence (*****) Date 03-09-2011 15:04
If the casting is Mag than it is not repairable with aluminum filler  :)

So you need to determine which material you have first.

Mag is 30% lighter than alum...  Experienced folks can simply tell be feel.

Mag is flammable.. Some drill or grinder shavings under an ox-fuel torch will ignite.. (safety first)

The safest way to test.. (if you absolutly cannot find out the mateiral by research) is to take a prepped section of suspect base metal (bright metal) and add a few drops of vinegar. If you see a reaction (bubble/etch) than you have magnesium.

There are also issues of surface prep... There are lots of threads on that for aluminum, mag equally sensitive to contamination...   Also there are balence control issues that come into play.. The Dynasty balence control settings are a bit different from transformer type power supplies and if too much EN is selected you can run into great frustration.
Parent - - By supermoto (***) Date 03-09-2011 22:19
I would agree that determining what material is crucial.

If the materials are either magnesium or aluminum casting what polarity and tungsten is best?
Parent - By Lawrence (*****) Date 03-09-2011 22:35
For fixing a motorcycle casting... AC

For tungsten... Anything but pure...  Thorium will do if you don't overheat it.

Lanthanum and Cerium are my favorites because they will work with AC or DC so there is no confusion if you sharpen both ends  :)

For dedicated AC   GTAW  I prefer Zirconium.
Parent - - By 522029 (***) Date 03-10-2011 12:22
Supermoto,

Don't use pure tungsten with the inverter  (Dynasty) machines.

Griff
Parent - - By supermoto (***) Date 03-10-2011 13:11
Thanks Lawrence, I will try this.

Griff,

I have used Pure plenty of times and it seemed to work fine on the dynasty. It is limited of course but seemed to good.
Parent - - By Lawrence (*****) Date 03-10-2011 16:05
Slightly off topic rant::::

Nobody should be selling/using pure tungsten electrodes.. It's the 21st century fellas.

At least don't spend any more coin on them... If you are so Dutch that you feel you must use up what you have?  Ok,.

The reason Miller recommends that pure tungsten not be used with their inverter based power supplies lies in the fact that pure tungsten does not have the alloying elements that improve the "work function" of GTAW electrodes. The "emitters" in Thorium, lanthanum, cerium and zirconium allow for better arc starts.  The capacitor discharge type of arc starting that are built into inverters is a little different than the High Frequency arc starters in transformer based power supplies.  This difference has an effect that makes arc starting more difficult with pure tungsten electrodes...  Will it hurt anything if you use pure tungstens with an inverter power supply?  No.

Spend the extra 5 bucks a box and buy cerium or lanthanum. Both of these work well with both AC and DC. Or if you are a dedicated AC aluminum person, Zirconium is also an excellent choice.
Parent - By supermoto (***) Date 03-10-2011 17:24
I don't mind spending $5 extra bucks, just what was available at the time.

Thanks for the explanation, much appreciated.
Up Topic Welding Industry / Technical Discussions / More casting ?s

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