- For good reason, magnesium alloys have long been used in various motorsport applications.
- The most common process for producing magnesium automotive parts and components is high-pressure die-casting. However, this process is only practical for large, well-financed operations.
- One alternative is sand-casting, more available to the small operation, and better for prototyping and iterating.
- This process was used in 2007 by a University of Michigan racing team to produce wheels for their competition car.
- Magnesium alloy may not always be the niche auto product it is now.
Though it is often considered an exotic or expensive material, magnesium is one of the most common elements on earth and, as an alloy, is comparable in cost to aluminum. Cast magnesium alloy is employed in many applications where performance under stress is required while weight must be minimized. For obvious reasons it has been in use in the automotive industry for years, especially for racing or high-performance applications: engine cradle for the Corvette Z06, cross car beam in the Jaguar X Type, engine block for BMW N52 engine…the list goes on. The most widespread application of magnesium alloy, however, is as a wheel material, an alternative to steel or aluminum.
In general, magnesium alloy components are best produced by some type of casting. The most common alloy employed in high-performance wheels is Magnesium AZ91. The specification AZ91 refers to the fact that the principal makeup of the alloy is magnesium with 9 percent (by weight) aluminum and 1 percent zinc added. Casting can be done in several ways. By far the most common process is die-casting, an industrial process which can produce alloy products with consistent properties quickly and on a large scale. In the die-casting process, molten metal is forced at high pressure into the mold: this works via a piston contraption. The piston contracts, pulling molten alloy from a reservoir. The piston then reverses direction, pumping the alloy into the mold. One of the advantages of this process is that the molten alloy cools suddenly on contacting the relatively cold mold. This quick cooling of the metal produces a cast piece with incredible strength and consistent composition. As the cast piece is ejected or a fresh mold is placed in position, the plunger goes through the same cycle again. If there is a detriment to this process, it lies in the fact that the shape of the object to be cast is set—there is little room for prototyping or iterating. This is a process for well-financed ventures that require a large number of a single component—not the case for most racing teams or motorsports enthusiasts.
One practical alternative to the die-cast process is sand casting. The sand-casting process begins with a prototype (in some other material) of the object to be cast. This prototype is surrounded by a sand-and-binding-agent mixture which hardens and forms the mold for casting. Molten aluminum is poured into the cavity left by the original object and allowed to cool, and the sand mold is knocked off, leaving the cast object. This process can be fairly rough and requires some machining to produce a finished piece. Also, the relatively slow cooling process means that the pieces can’t achieve the highest quality of their die-cast brothers. However, the process can certainly produce components of racing vehicle quality, built on the scale and to the demands of the user.
In 2007, the University of Michigan MRacing Formula SAE Team utilized the sand-casting system to produce new Magnesium AZ91 wheels for its competition car (which had previously used aluminum wheels). The team was able to go through a process of computer design, iteration, and hands-on production for their components that would have been impossible with the die-cast system. They used 3D printing to produce the prototype around which the sand cast was built, had the molds poured, tested the wheels for performance, and then used them on the car. By replacing their aluminum wheels with magnesium alloy wheels of their own design and manufacture, the team from UM was able to reduce wheel weight by roughly 25% while also improving stiffness.
Despite its reputation as a specialized or niche material, cast magnesium alloy continues to hold its own as a light, strong, and cost-effective alternative to aluminum or steel. As the quest for further efficiency and better performance continues, and with new advances in micro-engineering, magnesium may be poised to take a larger role in the vehicles of the coming years.
Magnesium in motorsports article:
University of Michigan MRacing Formula SAE Team’s scholarly article:
Wikipedia article: “Magnesium Alloy”
Wikipedia article: “Alloy Wheel”
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By Oscar P.