alot of the newer welding books have steps/tips on welding magnesium.. i'm not so much particularly interested in learning to weld magnesium as much as wondering what kind of parts are typically made of magnesium. steel i can recognize.. but perhaps i'm mistaking magnesium as something else... say, cast aluminum.
i occasionally get work to weld unknown aluminum castings.. when they dont weld, i attribute it to being and 'unweldable aluminum alloy' ... (i get good results welding aluminum otherwise)
but maybe its magnesium? and i should start learning how to weld it.
so the question is: what's magnesium usually used for? i must be used abundantly enough to warrant sections in welding texts.. usually bigger chapters than welding titanium, for example.
and how do i identify it?
aside from the fact that WELDING magnesium sounds downright dangerous after all the commotion in my highschool chemistry class, watching it explode into flames.
Not many. Magnesium is a lousy metal in service, because it corrodes like crazy and also has cracking problems. If you meet a "magnesium" casting, then the chances are that it's actually Elektron - an alloy of aluminium and magnesium. Aluminium's self-passivating oxide film protects against the worst of the corrosion.
If you find old copies of Flight magazine from the late WW2 period you'll see _lots_ of adverts for magnesium "The wonder metal that will rebuild our country when peace comes". Although it was developed enormously for wartime aircraft, its poor long-term service made it fall from favour by the early '50s.
In the '60s, Lotus racing cars were designed by Chapman on his "simplificate and add lightness principle". The "wobbly web" wheels of the type 23
so infamously unsafe today that they're no longer allowed on a track, and are replaced for competition
The "Kirk" bicycle of the late '80's was a cast magnesium frame. Not a bad road frame (until it cracked or turned to dust) but absolute rubbish as a mountain bike. There are many stories of them returning from rides in two halves.
Magnesium is a useful stiffening addition to aluminium alloys. Although the density of the casting isn't much less than another aluminium alloy, the extra stiffness may allow thinner walls. These are obviously lighter, but thin castings are also easier castings to make. This is why Volkswagen used it (intermittently and not universally).
Pure magnesium is mainly used as diecastings, because it has suitable properties for easy casting. AZ91 is the usual alloy (9% Al), either AZ91B or AZ91HP - trace elements (mainly iron) are reduced for the High Purity form, which improves corrosion resistance.
These days it's cropping up increasingly often, but it's mainly for its easy casting and light weight in relatively low-stressed consumer goods. The NeXT computer (the cube) had one of the first magnesium cases and they're now commonplace for cellphones.
A PhD chemist I work with used to work as a firefighter, both volunteer and paid, for quite a while. He said you have about ten minutes to put out a VW beetle fire before the magnesium catches. Once that happens, it takes about 5,000 gpm of water to put it out. Less water just makes it worse, due to the very exothermic dissociation and reforming of the water molecules caused by the intense heat.
He says they took a lot of crap from other fire companies once for having a "three alarm car fire", but they got it out (it was in a garage). Usually, once the mag case caught, they just let them burn.
One real good telltale that you may be deling with Magnesium is when the part seems to be too light weight for it's size.
Vinegar on a fresh scraped spot of bare metal will react with bubbles and a purpleish darkening.
Scrapings or filings will light on fire if they are fairly fine. This is the principle behind some emergency firestarters.
You will get your excersise trying to break a magnesium casting like a trasmission case or oil pan. The one Mag. oil pan I did break up nearly got me. With it on a concrete floor, a 12 LB hammer rebounded almost all the way back when I struck it. I nearly took the hammer on the forehead. Wicked rebound. I should have clued in then, but I got it broken up. Once I tested it, I junked most of it, as it was of no use for my casting use.
I do a lot of alum welding myself and checked into welding Magnesium but the process was more than I wanted to invest. What I was told is you need a sealed vacuum chamber to weld in so that the air bubbles can escape the metal. Anyhow I have several old engine cases made of Mag, The old VW air-cooled engines were magnesium, Porsche used a lot of it in there engines and transmissions, I had some aircraft engine case parts welded that were also magnesium, its very light weight, strong if its the right alloy and if its an old part it will be a darker grey in color not shinny like aluminum. The weight is the big difference, you can really tell when you compare it to aluminum.
.>A lot of earlier VW beetle crankcases are magnsium.
So for a time were the gearboxes of Bristol engined buses! After a fire when one was on a milling machine in the factory, extra flood coolant was installed, and special fire-fighting equipment around the machine shop.
From then on, all Bristol-engined buses and lorries with the magnesium boxes were identified externally by different - hexagonal - wheel hub centres - just so that fire crews etc could idenify them in an accident.