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  • Magnesiumn Question

    Is it true that Magnesiumn corrodes form ther Inside out? I faintly recall reading this many years ago. I am not sure though. I have some blocks of this stuff and thought of making some brake caliper hangers from it for my new Motorcycle.

  • #2
    Unless you know exactly which alloy of magnesium you have I would tend to go for some 7075 instead. You could compensate for the weight difference by using thinner sections of the stronger alloy.
    Gene

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    • #3
      It can cause the metal it is in contact with or bolted to to corrode.
      Especially if there is moisture and if a voltage is induced. Remember al the junk GM cars of the late 70's and early 80's where the bumpers would corrode right off the car. the bumper mounts where they were bolted to the frame just disolved. I would check the chart of galvanic reaction to see where that alloy stands.

      JL.........................

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      • #4
        Do you have a Class D fire extinguisher? Magnesium burns really well, especially when you put water on it. I won't machine magnesium even though I have some. The last thing I want is a metal fire.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          This is interesting. It's only 5 pages, the last one being very important.

          http://www.magnesium-elektron.com/da...20Brochure.pdf

          The stuff is just to strange to consider it for this application. Most of it is used for casting where strength can be gained by making it thicker where needed. Even then I would be surprised to see it being used as a mount for a vehicles brakes.

          In fact I think I have heard somewhere where it is illegal for use in certain applications, in and or around brakes for one.
          Gene

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          • #6
            The answer to his question is no. All metals corrode due to exposure to oxygen (air and/or water). He may have heard of hollow magnesium corroding on the inside due to oxygen exposure.

            As to machining mag, I'm with Evan. A class D fire is no fun.

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            • #7
              The O.P. may be thinking about "intergranular corrosion" which I assure you can happen internally, though I don't know if it happens in magnesium.

              Some Piper PA-28 and PA-32 airplanes had issues with intergranular corrosion of the extruded aluminum wing spars. Needless to say, it was not a good thing! Topical corrosion prevention does no good against intergranular corrosion, of course, because the electrical circuit is built into the metal.

              As I recall, the root of the problem was traced to some kind of a production issue at Alcoa in the mid 70's, of course that was no help to the people who had to replace their wing spars.

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              • #8
                Machining Magnesium is not a big deal. We machine center sections and side bells of quick change rears, as well as weld to repair cracks. We have never set the stuff on fire. However it IS POSSIBLE. A class D fire extinguisher is an absolute must have item. We have four of them in the shop, two in the fab section, and two in the machining section. Although I doubt you will have any trouble machining the stuff. We also make wheel nuts for sprint cars out of Magnesium, front steering and rear drive hubs are also a magnesium casting. Also wheel centers for sprint cars and late models are also magnesium. I think if magnesium was as easy to burn as people think, racers would accomplish the task on a regular basis.

                Having seen a good number of race cars drag a broken hub on the asphalt for over a mile, with sparks flying from the chassis dragging on the track, I tend to think the fire issue in a shop environment is a little over rated.

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                • #9
                  May be a tad hard to set magnesium on fire, but depending on the quantity of material, a paltry class D extinguisher wouldn't kill it. Especially if there were sufficient piles of shavings lying about. Ever see a landing gear fire? I watched an entire landing gear burn/melt down on a C-5A due to hot brakes (read- stupid pilot). Caught the wheel on fire. They foamed, and foamed, and foamed, and foamed the fireā€¦. And FINALLY put it out. But not before the front left main gear was all but gone, along with a lot of sheet metal and structure in the wheel well.

                  I have a little coil of it that I tear a piece off and light for the grandson once in a while. It is BRIGHT, SMOKEY, and COOL! But is also short lived and controlled.

                  I would opt for a good alloy of aluminum if it were me.

                  Just another $000,000,000.02

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                  • #10
                    It's pretty hard to "light" Magnesium unless it's in powder or thin sheet form. I've got some large pieces of it that took an acetylene torch to get started. The base on my vertical lathe is made out of it. I've drilled it and cut it with with no problems. You just need to take care of swarf and powder and not leave it laying around--About the same as Aluminum dust.

                    It burns brighter than the sun so don't play with it. But it does make cool blobs of melted dirt and sand.

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                    • #11
                      I just found some 7075 "magnesium" aluminum lug nuts on the net.

                      Yes 7075 contains magnesium. But that kind of magnesium won't catch fire.

                      Is it getting like that other tricky word, billet?
                      Gene

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                      • #12
                        There's only a few of the aluminum alloys that don't contain magnesium. Even 6061 has it. The sad part of using the magnesium alloys is that it must be coated. Well, not must, but if you want to keep looking nice it needs to be coated. It turns a dark grey and looks ugly in pretty short order. You won't have any problems machining it but I would stick to the aluminum alloys just because it's easier to get.

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                        • #13
                          I once did some machine work on a pair of valve covers off a double A dragster that were made of magnesium. I had no trouble machining them and tried to burn the shavings but couldn't. Magnesium only burns when you don't want it to.

                          Some time later was doing some welding on steel some 5 or 6 feet away and it (mag) caught fire in the middle of my shop. I scooped it up on a piece of plywood to take outside and when I did it exploded. It exploded because it had burned a hydraulic hose causing oil to get on it.

                          I'm 76 yrs old but nearly half the skin on my left arm is only 2 yrs old. Once is one too many.

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                          • #14
                            When I was in high school we had magnesium tape in the science lab. It came in short pieces about the size of a twist tie that you would put on your garbage bag. You could lite it with a match.
                            One day while in the dark auditorium I lit up a piece, you would think someone was welding in there. Got my ass booted out for that stunt.

                            JL..............

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                            • #15
                              Many wheels, and indeed brake housings on commercial aircraft are magnesium. And yeah, they will catch fire & burn.

                              "In fact I think I have heard somewhere where it is illegal for use in certain applications, in and or around brakes for one"

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