I am interested to hear what you consider more desirable in vinatge speed equipment. Who has arguments for the bennefits or drawbacks of either? I know Magnesium was the bee's knee's through the late 40's, 50's and into the 60's untill the EPA started cracking down on it. Are the differences in strength and weight that noticable? Outside of the nasty little burning habbit Magnesium has what else poised a concern with its use? Thanks.
The magnesium is definitely lighter. I personally like the look of magnesium, polished or not. The aluminum is a lot easier to care for.
magnesium reacts with oxygen,constantly . The white coating that magnesium has is an oxide of magensium and oxygen, MgO . While it looks crap,t actually protects the surface from further corrosion so each time you polish those antique wheels the coating is removed and the process begins again. A clean, unprotected magnesium alloy surface exposed to indoor or outdoor atmospheres free from salt spray will develop a gray film that protects the metal from corrosion while causing only negligible losses in mechanical properties. Chlorides, sulfates and foreign materials that hold moisture on the surface can promote corrosion and pitting of some alloys unless the metal is protected by properly applied coatings. The surface film that ordinarily forms on magnesium alloys exposed to the atmosphere gives limited protection from further attack. Eventually the entire object will break down with age,which is why antique rims are not used in vintage racing etc. MgO is harmless to humans and is often found in medicines ( milk of magnesia) and rock climbers use it on their hands to combat sweaty palms .There are dozens of industrial uses too. Two major magnesium alloy systems are available to the designer. The first includes alloys containing 2 to 10% Al, combined with minor additions of zinc and manganese. These alloys are widely available at moderate costs and their mechanical properties are good up to 95 to 120oC. The second group consists of magnesium alloyed with various elements (rare earth, zinc, thorium, silver etc) except aluminum, all containing a small but effective zirconium content that imparts a fine grain structure and thus improved mechanical properties. These alloys generally possess much better properties at elevated temperature, but their more costly alloying additions, combined with the specialized manufacturing technology required, result in significantly higher costs. So basically what i am saying that magnesium was lighter but costs and reliabilty was not as good or as cheap as the aluminum alloys that were later used.
I understand that magnesium alloys are now being used in modern engines to help save weight, in the search for better fuel economy. I don't know how they compare to the early speed equipment alloys, but I guess nowadays they would hope to be recycling the whole car in less than ten years anyway!
WOW! Good info! Any idea what recipe of magnesium was typically used on say wheels, manifolds, drivetrain parts, etc.? Would it have been the 10% Al flavor?
Strength? ,here are the figures . Magnesium Typical Physical/Mechanical Properties Density: 1770-1830 kg/m3 Melting Point: 650 °C Elastic Modulus: 44.8 GPa Poisson's Ratio: 0.35 Tensile Strength: 152-379 MPa Yield Strength: 80-280 MPa Percent Elongation: 5-15% and lots of info here on Aluminum. It depends on the alloys of aluminum when asking how strong it is,there being no definitive answer to any one question. http://en.wikipedia.org/wiki/Aluminium
Magnesium is being redevolped for use again car components with an Australian company leading the way. This is not to be confused with the old VW engine and trans cases ( burn baby burn.....) heres more here for those ewho like technical stuff. http://www.csiro.au/solutions/TMag.html CSIRO is a OZ government sponsored organisation for scientific research. They come up with lots of great stuff but often are let down by their political masters...
More great info. I have only found a few general foundries in America that still cast magnesium. Seems to be a lost art, or a heavily regulated one.
MacGyver used chunks of magnesium from a wheel and put it into a tube of some kind to make a little blow torch...
Mag is way cooler to me, mostly because of it's almost legendary status as the material of choice for the coolest of the cool parts from the 60's. Seems like the heart of every bitchin sweet factory drag car was topped with a cool magnesium 2x4 manifold, and they all rolled on some sweet mag wheels. This is also the same reason it is way out of my price range, so I get all the aluminum cool parts I can. Plus they don't make anything out of mag anymore so aluminum is the only material for new lightweight parts.
He didn't need one... he was a survivor! I on the other hand am not a survivor and must have hot rods and parts I can't afford made of aluminum or magnesium. Back to the thread. Just had a tourettes moment with my keyboard... sorry.
Generally Mag will have a 30-35% lower density than a comparable use Aluminum, which means less weight of the same amounts. as far as strength goes Mag tends to have a higher tensile strength with a lower yield strength. What that means is Mag will have a higher specific stiffness. Mag also demonstrates higher vibration damping. The molds for Mag can be cheaper to make for die casting because the pressure required is considerably lower. On the down side there are gases released during the manufacturing of Mag that have been classified as Green house Gases so Al Gore won't like you much.
Engineering data suggests that magnesium alloys are less susceptible to fatigue cracking than aluminum alloys (meaning that their fatigue life is longer in similar applications), which logically follows from the above mentioned vibration dampening property. Magnesium parts will still fail from fatigue long before steel would, obviously, but the increase in lifespan versus aluminum, coupled with the weight savings sometimes make its use worth the additional cost of production it brings with it. Older mag alloys got a bum wrap because they were more brittle than the lower grade aluminum alloys commonly in use at the time. If you had a mag wheel, and an aluminum wheel, the alum version would survive smacking a curb a lot better than the mag version would, because of the increased ductility. Those days have been over for decades now, but the stigma still gets tossed around sometimes. Modern mag alloys can be just as ductile as modern alum alloys, and conversely, some modern alum alloys can be heat treated to be as brittle as those early mag alloys. I believe that's called "coming full circle".
Who is Al Gore and what kind of Hot Rod does he drive? Thanks for all the input. Someone mentioned variations in casting procedures. Do those differences apply to sand casting?
There is 'very little to none' done in the way of sand casting commercially today. All wheels and engine parts are die cast . Don't forget that Audi have been building die cast body structures for their cars for years and Daimler Benz have been die casting cylinder heads since 1958 and blocks since 1978. They too are redeveloping the whole magnesium alloy formulation to reduce vehicle weight and save the planet through reduced fuel consumption.. The biggest problem with sand casting magnesium ,and this is 1930's technology which isn't even considered today, was that you got severe porosity and impurities because the molten metal would be reacting with the ambient atmosphere. Many racing efforts were thwarted when the use of magnesium cylinder heads couldn't be made leak proof. Magnesium oil pans are another and pictures of 1930's race cars can be seen covered in oil which literally sweated from the engine.
Against my advice, my brother bought a set of magnesium American wheels for his sedan. Not only did they oxidize instantly, but they were so porous that we had to have tubes installed. We ended up selling them to the guy who now owns the Larsen and Cummins roadster for his '55 Chevy gasser. When we had them they were polished to a mirror finish, but Willie (I think that's his name) liked them crusty looking and let them turn to black.
I've been running real magnesium American five spokes on the coupe for a few years now. I did a DOW7 coating but they are still dark. The rims are painted with an epoxy primer on the tire side so there's no need for tubes. I've been through one set of tires and when they were changed the bead on the rim showed a little corrosion but nothing bad.
Bedsides porosity, another problem with magnesium is that it outgasses or corrodes internally, so by the time the problem appears on the surface, there is most likely a hidden cavern inside. Think of it as behaving like pot metal. When you see the pimple on the surface, it is just the tip of the proverbial iceberg. Todays powder coating technology can give you a powder coat finish on aluminum that closely resembles aged magnesium. I have seen forty year old mag wheels in the raw which were scary and I would strongly recommend if you want to run magnesium wheels, that you have them X rayed and crack tested first - for your own safety and the safety of others.
Alfa thought it the bee's knee's and used it extensively by the early 30s. Here's a good run down on corrosion treatments http://www.patentstorm.us/patents/7101589/description.html
Chrysler uses mag for I/P castings. It is quieter and transfers vibrations at a lower amplitude to HVAC and other components to reduce future squeaks, rattles and vibrations. It is used in a crash component situation and gives a reliable future expectancy in impact situations. Think fatigued mini-van strikers or rusty Chevy pickup boxes. Expect to see alot more of the stuff diecat into structural parts. Seat frames, maybe cross members could easily be made with the product. Light and predictable is future of automotive materials. You heard it on here first. It is going to become a common material at the pick a part. It will be worth learning how to cast or fabricate with it.
Magnesium is lighter than alum & cost more but remember they use Magnesium in fireworks for the pretty bright light that is very hard to put out when burning !!
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