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 dimen- sions 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. Shrinkage rates are more consistent and predictable in magne- sium than in other nonferrous metals. Components release from the die with minimal force and distortion, hence they have minimal residual casting stress.


• Impact & Dent Resistance—Te elastic energy absorption characteristics of magnesium result in good impact and dent resistance and energy manage-


Types Magnesium alloys


Fig. 1. Magnesium’s light weight has made it a useful alloy for a number of new markets and applications, such as the automotive, power tool, computer and electronics industries.


ment, 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 pos- sess a low galling tendency and can be used as a bearing surface in conjunction with a shaft hardness above 400 Brinell.


can be divided into two groups: sand casting alloys and diecasting alloys. Alloys also can be classified as general purpose, high-ductility and high-temperature alloys. Most mag- nesium alloys are produced as high-pu- rity versions to reduce potential corrosion problems associated with higher levels of iron, nickel and copper. Sand casting alloys can be produced with a fine grain structure due to


small additions of zirconium. Aluminum is the principal alloying


element for many magnesium alloys, as it can improve the mechanical strength, corrosion properties and castability of magnesium castings. Te most widely used general purpose sand casting alloy is AZ91. In the alloy nomenclature, the letters A and Z denote the major alloying elements, aluminum and zinc. However, not all properties improve with aluminum


2012 Casting sourCe DireCtory


Metal Casting Design & PurChasing


37


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