[IisChas]

I work on a competitive design team and one of the biggest factors in our design considerations is weight. As such, using magnesium in place of aluminum is very enticing to us. I’ve already been working on getting ready to mill it, but we were recently donated a plasma cutter. It’s nothing special, with no air-tight enclosure and a standard water bed underneath. I already understand the risks if/when something goes up in flames. We’ll have buckets of sand and type D fire extinguishers ready, in addition to training, etc., etc.

That leads me to my question: is it even possible to cut magnesium over a water bed in normal atmospheric conditions? I’ve seen some people successfully plasma cut magnesium with handheld cutters, but I haven’t found any good resources for CNC cutting. My assumption is that the burning remains of the magnesium would fall into the water and create a runaway Hindenburg, but I’m wondering if anyone has any prior experience. Thank you.

[peteeng]

Hi Chas - From what I gather using water on burning Mg is a no no as it produces H2 gas which burns more. Why are you bothering with Mg when you should go to carbon fibre? same stiffness as Al yet 1500kg/m3 vs 2700kg/m3 for AL. I made a couple of Mg and titanium bicycle frames some 30 years ago and the Mg material was difficult to work, difficult to get the right alloys and its not that strong. If you get the strong alloys they are very brittle. The Ti bike frames used Ti6-4. I make CF plates that are E=70-80GPa at 1500kg/m3 and 950MPa flexural strength in my garage. If you look at videos of metal fires or speak to firepeople that haver fought metal fires you really don't want to do it. The energy levels and speed are huge. Same as machining it the swarf can spontaneously combust... be very very careful in fact don't do it... Alcoa used to publish excellent books on this sort of thing, they must be online now... But CF is the answer for you, thats how all high performance structures have gone... Steel, alum, carbonfibre soon to fullerenes. Peter most mg structural applications have been replaced by CF. Even car and racing wheels are CF now vs forged Mg. Alcoa closed its Mg plants some 20 years it seems...

if its strength you need even glass fibre laminate like G10 will get you to 900MPa at 1800kg/m3 way past AL. Do you need strength or stiffness? attached data sheet shows G10 at 500MPa strength the stuff I make is much stronger at test. Look up infusion great process.

edit if you can get intermediate modulus fibre then 100GPa is easy at 1500kg/m3... if you have seen videos of "Mg" plate it maybe a AL/Mg alloy not a true Mg alloy.

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