Magnesium alloys?

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John Hill
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Magnesium alloys?

#1 Post by John Hill » Mon Aug 17, 2020 5:34 am

We have received a Goblin engine to add to our museum collection. It some ways it is quite a gem with apparently all hoses, connections, ancillaries and plates etc. Unfortunately it has been 'stored' outdoors for a couple of decades and the big magnesium(?) casting is covered in a thick layer of corrosion.

Online I can find a thousand and one recommended processes for cleaning the corrosion so I thought I would ask here and maybe get something that would be within our capabilities!

Thanks, John
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Re: Magnesium alloys?

#2 Post by ian16th » Mon Aug 17, 2020 9:10 am

How do I clean corroded alloy wheels.

It seems that WD40, wire wool and elbow grease are the place to start.
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Re: Magnesium alloys?

#3 Post by Pontius Navigator » Mon Aug 17, 2020 9:38 am

John, try a yacht Chandler, they will have more need for fixing that sort of corrosion.

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Re: Magnesium alloys?

#4 Post by John Hill » Mon Aug 17, 2020 9:48 am

ian16th wrote:
Mon Aug 17, 2020 9:10 am
How do I clean corroded alloy wheels.

It seems that WD40, wire wool and elbow grease are the place to start.

Thanks but I believe no other metals are to be allowed to touch the magnesium, otherwise probably OK for a small piece.
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Re: Magnesium alloys?

#5 Post by John Hill » Mon Aug 17, 2020 9:50 am

Pontius Navigator wrote:
Mon Aug 17, 2020 9:38 am
John, try a yacht Chandler, they will have more need for fixing that sort of corrosion.
Tahnks, we are only 80kms from the nearest boat yard so I might just pay a visit down there.
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Re: Magnesium alloys?

#6 Post by ian16th » Mon Aug 17, 2020 10:02 am

John Hill wrote:
Mon Aug 17, 2020 9:48 am
ian16th wrote:
Mon Aug 17, 2020 9:10 am
How do I clean corroded alloy wheels.

It seems that WD40, wire wool and elbow grease are the place to start.

Thanks but I believe no other metals are to be allowed to touch the magnesium, otherwise probably OK for a small piece.
How about a coarse plastic pan scrubber instead of the wire wool?
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Re: Magnesium alloys?

#7 Post by om15 » Mon Aug 17, 2020 12:30 pm

Selenious acid, wash off with clean water.

The thing with mag alloy castings is that the corrosion does tend to go right through, apply the acid by placing paper towel over the pitted area, paint the acid onto the towel until it is soaked in the stuff, leave for half an hour, wash off, do not get it in your eyes and wash your hands before going for a pee.

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Re: Magnesium alloys?

#8 Post by om15 » Mon Aug 17, 2020 12:34 pm

Found this which might be of interest

https://patentimages.storage.googleapis ... 961030.pdf

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Re: Magnesium alloys?

#9 Post by TheGreenGoblin » Mon Aug 17, 2020 1:49 pm

Some useful advice herein as well...

Corrosion control of aircraft

See section six for magnesium alloys.

As per advice already given...
Mechanically remove corrosion products when practicable. Use stiff bristle brushes and similar nonmetallic cleaning tools for such mechanical cleaning, particularly during treatment in field conditions.

6.60.2 Any entrapment of steel particles from steel wire brushes, steel tools, or contamination of treated surfaces by dirty abrasives can cause more trouble than the initial corrosive attack.

In-Place Treatment of Magnesium Castings. Magnesium castings, in general, are more porous and more prone to penetrating attack than wrought magnesium skin.

Treatment in the field is usually the same for all magnesium areas. Engine cases are among the most common examples of cast magnesium in modern aircraft. Bell cranks, fittings, and numerous covers, plates, and handles may also be magnesium castings. When attack occurs on a casting, apply the earliest practicable treatment to avoid dangerous corrosive penetration. Engine cases in salt water can develop “moth holes” and complete penetration overnight.
I presume you are not attempting to achieve airworthiness but just achieve a reasonable finish and ensure further protection of the engine?

More useful stuff here too...

Surface treatments for Magnesium Alloys
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Re: Magnesium alloys?

#10 Post by om15 » Mon Aug 17, 2020 2:53 pm

The thing with mag alloy corrosion is that it is rarely "surface" corrosion but is intergranular corrosion coming from the inside, Rolls Royce used mag alloy in the air inlet casings on the Dart, in over 20 years Dart maintenance I never saw corrosion, this due mainly to the paint and paint application process. However on the Garrett TPE331 fitted to the Dornier 228 the front gearbox mag alloy casings were pretty dreadful for corrosion, on aircraft with low operation altitudes (fisheries patrol), we were pulling engines for replacement gearboxes at under 1000 hours.
It may well be that what you are seeing is the original paint finish coming away, one method of restoring your engine might be to remove all accessories, looms, firewire and so on, and use a hand held grit blaster (preferably with plastic grit) to remove all surface loose paint, clear the loose stuff away and treat with selenious acid to stop further attack, then treat with original spec primer and top coat, these will still be available, if they are not available equivalent specs will be,
these people can advise

https://www.praxairsurfacetechnologies. ... ft-engines

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Re: Magnesium alloys?

#11 Post by John Hill » Mon Aug 17, 2020 9:00 pm

Thanks for all that good information.

I will be going out to look at the engine again tomorrow armed with my newly acquired expertise in the field of magnesium corrosion.
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Re: Magnesium alloys?

#12 Post by om15 » Tue Aug 18, 2020 5:53 am

John, could you post some photos (close up) of the problem, be interesting to see exactly what has occurred.

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Re: Magnesium alloys?

#13 Post by John Hill » Tue Aug 18, 2020 6:08 am

om15 wrote:
Tue Aug 18, 2020 5:53 am
John, could you post some photos (close up) of the problem, be interesting to see exactly what has occurred.

Sure, I will take a camera with me tomorrow.
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Re: Magnesium alloys?

#14 Post by John Hill » Wed Aug 19, 2020 5:51 am

I went to the local tractor shop and bought the biggest compressor that we could run on the single phase power in the workshop, 16cfm, 3 hp, I also got a sand hopper and a gun to go with it. I expect we will have time to give it a test soon but not before we get the three wheeled refueler out of the workshop and and our 'new' Cessna 410 air rescue delivered and under cover.


Image

Just the one picture as I doubt my sanity would survive getting another hosted and displayed here, John.
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Re: Magnesium alloys?

#15 Post by G-CPTN » Wed Aug 19, 2020 6:40 am

John Hill wrote:
Wed Aug 19, 2020 5:51 am
Just the one picture as I doubt my sanity would survive getting another hosted and displayed here, John.
Image not displaying for me.

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Re: Magnesium alloys?

#16 Post by John Hill » Wed Aug 19, 2020 6:44 am

G-CPTN wrote:
Wed Aug 19, 2020 6:40 am
John Hill wrote:
Wed Aug 19, 2020 5:51 am
Just the one picture as I doubt my sanity would survive getting another hosted and displayed here, John.
Image not displaying for me.

I may have to have a cup of tea and a lie down... :( :(
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Re: Magnesium alloys?

#17 Post by John Hill » Wed Aug 19, 2020 8:10 am

I hope these will work??

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Re: Magnesium alloys?

#18 Post by om15 » Wed Aug 19, 2020 8:51 am

Ah, I see, how much money have you allocated to this?

Method 1, complete disassembly of accessories, fuel pipes, looms and so on, split the casings and send away for cleaning, chemical treatment, priming and application of top coat, re assemble.
Method 2, use a small stiff brush and slowly work around the casing removing loose and flaking material, paint the casing with selenious acid, wash off, prime and apply top coat with a small brush.
Method 3, display as is to demonstrate the effects of corrosion on mag alloy.

A challenging job, good luck with it and keep us updated.

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Re: Magnesium alloys?

#19 Post by Wodrick » Wed Aug 19, 2020 9:25 am

A challenge indeed
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Re: Magnesium alloys?

#20 Post by Boac » Wed Aug 19, 2020 9:45 am

I think you'll be very lucky to get anything 'split' or 'undone' on that! Good luck indeed.

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