You can call just about any steel foundry, the one that made that casting would probably be the best one to let you know the chemistry of the part to know what electrode would be best to use on it. They would also have the weld procedure to make repairs to that particular casting. All foundries that make steel casting usually have a rpair procedure for each casting.

Andrew,

Lets start with safety. Magnesium (Mag) is a flammable metal, in this case flammable metal means a metal that produces its own oxygen when burning. Breaking the Fuel/Heat/Oxygen cycle is nearly impossible once the stuff gets going. Metal-X fire extinguishers and buckets of sand are necessary to cover burning Mag. Magnesium will literally burn under water. Do NOT use your regular shop ventilation to remove mag grinding particles and dust. Some shops use modified paint booths, which pull the dust into a water medium. Most people cannot or will not invest in the necessary safety measures, however please do use extreme caution if you're doing a lot of grinding of mag.

There is a lot to cover as far as weld repairs of Mag castings go. The more complex the casting geometry the more strictly guidelines should be followed. Firstly you need to identify the type of magnesium alloy you are dealing with. Now with you in Australia and me in the US we may have to work a bit to define terms. None the less, Preheat, inter pass temperatures and postheat as well as filler wire selection are all going to be governed by the specific type of casting your dealing with. Here in the US. We deal with several predominate types, here is a listing of some that I have worked with personally.

AMS4418 …………………Trade name QE22A (Alloyed with Rare Earth and Silver),
AMS4434 …………………Trade named AZ63A (Aluminum Zinc)
AMS 4434 and 4484 ………Trade named AZ92 and AZ92A (Aluminum Zinc)
AMS 4442 …………………Trade named EZ33A (Rare Earth and Zinc)

Now rather than write an entire lecture I'm going to wait to see if you can identify the type of metal you're proposing to work with. Once that's established we could talk about the very important Preheat techniques, Manual TIG repair, Electrode Selection, the effect of hotwork on Temper/ Designations, Shielding Gasses or mixtures, InterPass temperatures, Distortion restraint, grinding and surface prep, and a whole lot more.

The best suggestion of all would be for you to gain access to the AWS Welding Handbook Volume 3 Eighth Edition which gives detailed guidelines in over 40 pages dedicated specifically to Magnesium.


The Ball is in your court.


Lawrence

Andrew

Were you able to acquire AWS Welding Handbook Vol. 3 Materials and applications?

I'm not familiar with auto castings; my Mag. experience is strictly with aircraft. None the less, differential castings sound pretty critical. So to give advice without knowing what we deal with makes me nervous.

Here is the tricky part. Whilst Professor Crisi correctly acknowledges that Magnesium is most susceptible to corrosion and in obedience to the second law of thermodynamics, really likes to return to its oxide form. And while *some* magnesium castings contain as much as 10% aluminum we need to be equally clear that as many as 50% of the types of magnesium castings to be found today are NOT alloyed with aluminum. Zinc and or Zirconium being added instead. The composition of the casting, as stated in my last post, has an effect on Pre/interpass/post temperatures and is critical to filler metal selection. While guessing sometimes works, the wrong filler wire will necessitate the removal of all deposited metal and the diluted parent material as well, only then can a sound weld be made with the correct filler if you guess correctly the second time.

This all sounds complicated only because we lack data. Once you know what your working with the actual welding is pretty routine. If the casting is a good one, Mag. Can be welded with relative ease.

The tables in the AWS handbook provide an excellent source of data and if you are going to have to experiment on scrap material, (due to lack of response from your foundry) it may be wise to acquire a copy before you begin. If you must make general assumptions it will be invaluable.

If you cannot do these things, Here are a few rules of thumb, which apply to nearly all Mag. Castings.

1) No old filler wire. If the wire has been exposed to air for more than a month or so chuck it. Unless fresh out of a new sealed package, clean with fresh scotch brite until a *bright* surface is achieved than wipe down with Acetone or Alcohol.

2) Route out entire flaw. Cracks hold impurities, which will foul any attempt to cover them over. Argon backup on any part which may melt thru or has been routed completely thru.

3) Preheat the part in an *oven* <pick a day your wife is gone> with at least a 60 minute soak time. No rosebuds!

4) Cover entire part with an insulation blanket during welding operations leaving only the weld area exposed. Return to oven as necessary to keep heat uniform.

5) If multiple passes are required use tempstick to stay within interpass temperatures.

Keep us updated and good luck

Lawrence