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Magnesium rot

farmguywithasaw

farmguywithasaw

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Anyone aware of what causes this stuff to “rot” away. I got a couple of case halves for a 365 that in putting together and there is a bit where the muffler brace bolts on and the falling dog. Any tips to prevent and repair said issues. Thanks for the interest.
 
Conquistador3

Conquistador3

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I can give you a lesson in chemistry of the materials if you like. :laugh:

Suffice to say that being a metal with high electrochemical activity, most magnesium alloys have a tendency to corrosion in certain situations.
Among the stuff that can result in really bad corrosion are:
salt solutions, including chlorides dissolved in freshwater
all mineral acids bar HF
anhydrous methanol
halogenated organic compounds (only at high temperature)

Generally speaking magnesium will develop a thing gray patina (passivation in old chemists' parlance) when exposed to atmospheric humidity or water sprays that protects the underlying metal but when moisture is trapped on the surface by dirt, that patina will be eroded very slowly due to the aforementioned electrochemical activity, leading to the most common form old magnesium rot. The presence of contaminants such as chlorides will accelerate the process.
Contant high air humidity (over 80%) will also speed up the corrosion process.

Your standard pro-grade chainsaw is usually treated to prevent magnesium rot, or at least to slow it down but there's no cure for poor material handling. Keeping the saw clean and storing it in a low humidity environment will help bunches.

Personally I am not a fan of magnesium repairs, especially in areas like felling dog and anti-vibe attachments, but some people here have attempted repairs.
 
Canyon Angler

Canyon Angler

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One thing that I think really gets the rot going is any form of alkali/base such as lye or oven cleaner or ammonia or even the lime in concrete. If you set aluminum alloy down on bare concrete (like the bottom of an outboard motor skeg -- where the paint is worn off -- against a concrete slab), the lime in the concrete will attack the aluminum alloy. I believe magnesium will also do the same thing, even faster. So you need to be careful if you use a base like ammonia or Simple Green to clean grease off a magnesium chainsaw, and be sure to rinse it all off really well.

I know with boats, in saltwater, you use a zinc anode on a stainless steel or monel prop shaft or on an aluminum-alloy outdrive, and the zinc will disappear before the aluminum (or stainless steel or monel). But if you're boating in freshwater, you can use a magnesium anode (instead of zinc) and, since it's even less "noble" than zinc, it will even protect zinc in fresh water. (But don't use magnesium anodes in saltwater, because they'll disappear faster than you can attach them.)

Magnesium is weird stuff. I've seen videos where if it catches on fire, it burns so hot that if you try to extinguish it with water, the hydrogen and oxygen in the water will dissociate, and putting water on the magnesium fire is like putting gasoline on an ordinary fire, because the hydrogen ignites... or something like that.
 

TLG

Komatsu Iron Life
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Agree with what Canyon Angler said above. He speaks the truth. Being around mining machines that use a lot of magnesium cast parts for wear items. No burning or hard facing rules apply as it will light up. And yes using water on a magnesium fire is like putting gasoline on a fire LOL!!!!
 
farmguywithasaw

farmguywithasaw

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Well this saw was road hard and put away wet from the look of it. It was also full of used engine oil when I got it and I imagine the corrosive acids and alkaline compounds that develop in used oil. led to the corrosion. I noticed that it really discolours the plastics too
 
Franny K

Franny K

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It is cast magnesium that seems to rot. The welding rods as well. Magnesium concrete tools seem pretty free of this phenomenon. Perhaps some additives to make it flow into the molds easy? There is a scale of voltage produced in the corrosion or needed to stop it and Magnesium is way on one end and gold on the other.
 
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