Magnesium Profile

Magnesium has a density two-thirds that of aluminum and only slightly higher than that of fiber-reinforced plastics and possesses excellent mechanical and physical properties. When coupled with the inherent advantages of the metalcasting process, magnesium alloys yield cost-effective solutions to product needs by allowing for part consolidation and weight savings over other materials and manufacturing methods.

Advantages of Magnesium
Magnesium alloy properties can provide a casting designer with several advantages over other lightweight alloys.

Weight—The lightest of all structural metals, magnesium preserves the light weight of a design without sacrificing strength and rigidity. This benefit is important when portability is a key element of the product design, such as with chainsaws, pneumatic nailers, circular saws, luggage, laptop computers and cellular phones. Automobiles and other transportation equipment continue to take advantage of magnesium’s low density in expanding application areas ranging from under-hood and driveline uses found in engine brackets and transfer cases to numerous interior parts, such as steering column components, pedal brackets, instrument panel supports and seating.

Damping Capacity—Magnesium is unique among metals because of its ability to absorb energy. Increased vibration absorption capacity provides for quieter operation of equipment when magnesium castings are used for housings and enclosures.

Dimensional Stability—Annealing, artificial-aging or stress-relieving treatments normally are not necessary to achieve stable final dimensions. Metallurgical changes in the structure of some metals can affect dimensions after prolonged exposure to elevated temperatures, but this is not the case with magnesium alloys. As a result, there have been few problems associated with the dimensional change of castings in assemblies. Magnesium shrinkage rates are more consistent and predictable in comparison to other nonferrous metals. Components release from the die with minimal force and distortion, hence they have minimal residual casting stress.

Impact & Dent Resistance—The elastic energy absorption characteristics of magnesium result in good impact and dent resistance and energy management, which is one reason magnesium castings can be used for automotive safety-related applications, such as air bag systems. Portable tools and handheld electronics also benefit from this combination of properties, offering mechanical shock resistance.

Anti-Galling—Magnesium alloys possess a low galling tendency and can be used as a bearing surface in conjunction with a shaft hardness above 400 Brinell measurement

Design consideration

When evaluating the various alloys and processes for a magnesium casting, a number of characteristics should be considered to obtain a quality, low-cost component. These include the end-use application, the post-casting operations and tooling costs.

High Stiffness-to-Weight Ratio—This characteristic is important where resistance to deflection is desired in a lightweight component.

Improved Die Life—Unlike molten aluminum, molten magnesium does not react with tool steels, resulting in longer die life and increased productivity. Because of low erosion and reduced heat input, which reduce the propensity for thermal fatigue (heat checking of the die), casting magnesium can achieve three to four times the die life than can be achieved with aluminum.

Machining—Magnesium is recognized as the easiest of structural metals to machine and is the standard of the cutting tool industry when comparing machinability of metals. The low power requirements for machining magnesium alloys permit the use of deeper cuts and higher feed rates, thus permitting fast and efficient machining when compared to other metals. Magnesium alloys also normally produce well-broken chips, which are easy to handle.