Need help repairing this (magnesium welding)

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Hi guys,    I need some advice on repairing this cast magnesium brake assembly, and particularly, WELDING MAGNESIUM.   First, I know i'll be asked so:      I know it's magnesium because it's light, soft (I can cut it with my pocketknife), the shavings react to vinegar and most of all because it's stamped "magnesium".        I'm assuming it's cast only because I'm thinking it would be easier to mass-produce them that way rather than machining each one.  If i'm wrong on this assumption, someone please correct me.  Also, there are no existing welds on it, so I'm only assuming that it is a weldable alloy of magnesium.What needs repair:   As you can see, half of the threaded hole (I'm going to refer to it as the "nut") at about the 7 o'clock position is broken.  My intention was to completely remove the broken nut and then machine a similar sized piece of magnesium, drill & tap it then weld it back on.  Seems simple, right?           The first problem I ran into was that my two nearest metal retailers do not sell magnesium- in fact the "Metal Superstore" (which is a large chain) even indicated that nobody has ever asked for magnesium before!  So, finding magnesium around here might be impossible.So, question 1:  does anybody (particularly those in British Columbia) know where I can find a small piece of magnesium.  Or does anybody know an online place that will ship a small piece?Question 2:   If I can't find magnesium, what can be welded to magnesium?  Since the process to weld it is somewhat similar to aluminum, is there any aluminum alloy that can be welded to it?  I understand I could simply braze a piece of mild steel to the magnesium however this would only be a fraction of the strength that I'd get from TIG-ing it.Any advice would be appreciated. Attached ImagesLincoln AC225 & MigPak 140, Lincoln Magnum SpoolGun, Miller Spectrum 375-X Plasma, Syncrowave 200 TIG, Millermatic 252 MIG, Miller Digital Elite, General 7x12" horiz/vert bandsaw, 3' box/pan brake, 20 ton press, milling machine, 12x28 lathe, etc.
Reply:Oh, just to avoid any sidetracks I should add that I'm aware of the safety implications surrounding the flammability of magnesium (particularly the filings and shavings) and what could happen if the weld fails on a brake assembly.  Lincoln AC225 & MigPak 140, Lincoln Magnum SpoolGun, Miller Spectrum 375-X Plasma, Syncrowave 200 TIG, Millermatic 252 MIG, Miller Digital Elite, General 7x12" horiz/vert bandsaw, 3' box/pan brake, 20 ton press, milling machine, 12x28 lathe, etc.
Reply:no experience welding magnesium  but if you can is there anything on the  othere side were the broken nut is that would stop you from drilling a hole and making a new piece and bolting it to the magnesium?
Reply:No experience with Mg, but if that was an aluminum part it would be very easy to build up the broken part with weld, and re-drill/tap it.  Maybe that would be the best choice here as well.Have we all gone mad?
Reply:I am no expert in welding magnesium, but do believe that using the correct alloy is important; an improper alloy can lead to intergranular corrosion, I think. I'll let someone else cover that subject fully, though,I will suggest that if you aren't sure of the strength of the finished part, you may be able to make a steel piece to cover the outside of the boss and epoxy it in place to get some added strength, assuming this isn't a show bike but that performance is important. I would use an epoxy which could withstand the highest temperatures, due to heat being generated in the drum eventually warming the hub. Stainless might even look good there!
Reply:Snowboarder's suggestion would be the way i'd go about that sort of repair, there's some threads around using that technique on Al castings- using a bolt/mandrel to make remachining the thread easier. Can't weld aluminium to mag cause it'll result in brittle intermetallics. Dissimilar joints are out with the kit you've got available AFAIKLooks to me like the shoe mountings would interfere with a bolted fix leaving welding the only viable option. Given the cost of mag filler wire (if you get a quote make sure you're sitting down and medicated!) i would be looking for a replacement or if that part's rarer than rocking horse poo consider subbing the job out to someone that works with mag on a regular basis (almost certainly be cheaper than buying a kg of filler wire)Probably the best resource freely available for mag alloys is http://www.magnesium-elektron.com/, there are detailed pdf's covering pretty much everything including pre and  PWHT of the various different alloys, welding techniques etc.
Reply:Instead of machining off and welding a new "nut" on, just drop a undersized piece of carbon rod in the hole so it won't weld closed and build up whats missing from filler. And the filler is expensive! If I remember right there are two popular grades of filler, with the percentage of aluminum the major difference. Being that you will be welding an "edge" there should be no need for extensive pre/post heat, but some surely won't hurt. Weld up against carbon. Drill out carbon with drill size used to prep hole for tapping, then tap hole.Peter
Reply:Could you mill it off then drill and tap the hole.Take a nut the right size then weld a stud to it and thread it in the hole with some locktight on it?that would probably be as strong and would eliminate the mag welding.After the arc has died the weld remains
Reply:yeah , definately like he said...........definately end mill (face mill) those two nubs , drill and tap , wala.        thermal arc 252i  -  millermatic 350P -   miller XMT, cp300ts, 30a 22a feeders, buttload of other millers, handfull of lincolns, couple of esabs  -   Hypertherm 1250 G3
Reply:Hello aquafire, magnesium can generally be welded with GTAW very readily. I know of a couple of options for you to consider here. First one, using a rotary tool with a carbide cutter carefully clean the entire area around the broken part and clean all of the surfaces of the broken section. Then using magnesium filler rod weld and build up the area to the proper profile and drill and tap a new hole through the built-up portion. With GTAW there is no fire hazard to welding magnesium(however, if you are grinding magnesium you need to pay attention to the dust as it can be ignited with open flame). Second possiblity, find a stainless steel bolt of the same size and thread pitch as the original piece that was connected in the broken area. Carefully clean all of area of the break except for the threaded area that is exposed with the rotary carbide cutter. Line up and lay the threaded portion of the stainless steel fastener into the threads that are left on the hub. Now start welding and building up around and over the top of the bolt from the broken tab ends until you have them connected and the bolt is encased with the weld that you have applied. You should be able to unscrew the bolt now and be left with formed threads. This is possible because the magnesium will not stick to the stainless steel material. The bolt acts as a form. This would be my second choice for repair, the first option is the one that I would likely use myself, although I have done it both ways. The other posters were right when they mentioned that magnesium filler is expensive and sometimes you have to buy a minimum amount so look out. If it turns out that you can't justify the cost of filler you could possibly find some other magnesium castings or parts and saw some strips off of them and use these for filler, sometimes you just have to get creative. Keep us informed on your progress. Good luck and best regards, Allanaevald
Reply:Whoa    Firet rule aluminum to aluminum----Magnesium to magnesium     this is not a tuff fix. first make a template of how much build up you need to replace the broken boss  tig weld just as if it were aluminum only use magnesium filler rod. make sure it is clean. Mag dosen't take quite as much heat as alum. you mite like to do a few test first.  i'm sure that you can find mag filler rod at your local welding supply. Make sure you strip and remove anything that the heat could damage. Now if you can tig you can do it. build up--machine--redrill hole--and tap. presto now you can go for a ride.  ? you mite be thinking if I have done this before. the answer is many times. GOOD LUCK GO FOR IT
Reply:That little threaded post portion is also slotted isn't it? Slotted so the cable can pass through?"The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Hmmmm...... Yamaha Enduro? Don't have any answers for you but it looks like the front brake on a couple of old enduros we've got sitting around.... one has a magnesium gear case that has several small cracks.HH 187Miller Bluestar1EAHP AlphaTig 200X
Reply:Easiest thing would be to build it up with magnesium rod, clean it up with a grinder drill and retap, pretty much as Pro-X-60 said. Not hard to do.....Mike
Reply:Thanks for the advice guys- some really good advice.  This is a case of easier said than done:   I tried (and tried HARD) to find magnesium rod! I tried 7 welding supply companies in the area (a few of them big chains) and none of them stock it.  The best I could find is one that said they could order it in, but only if I bought at least 1 pound (about $360).  I'm hoping another one might be able to get a "sample" from one of the manufacturers (probably 1/2 rod- which is really all I need).   With all the magnesium engine blocks and other automotive components made of magnesium, why are the rods so damn hard to find??!?!?!   Lincoln AC225 & MigPak 140, Lincoln Magnum SpoolGun, Miller Spectrum 375-X Plasma, Syncrowave 200 TIG, Millermatic 252 MIG, Miller Digital Elite, General 7x12" horiz/vert bandsaw, 3' box/pan brake, 20 ton press, milling machine, 12x28 lathe, etc.
Reply:Have you considered an epoxy and helicoil?
Reply:Posted by AquafireThanks for the advice guys- some really good advice.This is a case of easier said than done: I tried (and tried HARD) to find magnesium rod!I tried 7 welding supply companies in the area (a few of them big chains) and none of them stock it. The best I could find is one that said they could order it in, but only if I bought at least 1 pound (about $360). I'm hoping another one might be able to get a "sample" from one of the manufacturers (probably 1/2 rod- which is really all I need).With all the magnesium engine blocks and other automotive components made of magnesium, why are the rods so damn hard to find??!?!?!
Reply:With all the magnesium engine blocks and other automotive components made of magnesium, why are the rods so damn hard to find??!?!?!
Reply:Hey what bike is that off of by the way? I had the same thing break on my old RM 250 It was way before i got trained in the welding feild so i never tried to weld it so i just replaced it. The first one i found was 300 bucks, i looked around and found another for 100. Maybe I or somebody else could help you find a replacement unless your heart is set on welding it.Nothing Ever Got Done By Quitting, Never Give Up.
Reply:Aquafire,I found this place in Canada that will sell small quantities.  I'm down to my last rod and would be happy to split a pound with you.JimWe have a $50.00 min, $5.00/ea. Or $70/lb. for extra small quantities upto 1 lb.We have AZ61, 1/16" and 1/8" dia in stock.Regards,JohnM&B MAG LTD197 Toryork DriveToronto ON M9L 1X9CanadaTOLL FREE 1 877 749 9461LOCAL 416 749 9461FAX   416 749 5023Web: www.mandbmag.comE-mail: [email protected]
Reply:Im also glad to help. I can fix this for $20. check out www.oasismotorcyclecenter.com  unfortunately Im in Miami, FL. We also have magnesium rods for sale AZ92A. you can buy one rod or more. or go to ebay here let me know.
Reply:Originally Posted by Doug247Hey what bike is that off of by the way? I had the same thing break on my old RM 250 It was way before i got trained in the welding feild so i never tried to weld it so i just replaced it. The first one i found was 300 bucks, i looked around and found another for 100. Maybe I or somebody else could help you find a replacement unless your heart is set on welding it.