MAGNESIUM


CASTING PROCESS COMPATIBILITY While the majority of magnesium production is via diecasting and sand


casting, other processes have been developed: • Permanent mold. • Plaster mold.


DESIGN CONSIDERATIONS • When evaluating alloys and processes for magnesium, the end-use applica-


Typical Mechanical Properties of Common Alloys Alloy


Ultimate Strength (ksi)


AZ91


AM60 AM50 AM20 AS41 AS21 AE42


224 225 210 190 215 175


230


160 130 125 90


140 110 145


Yield Strength (ksi)


Elongation %


3 8


10 12 6 9


10


Hardness Bhn


70 65 60 45 60 55 60


Converting this military helicopter transmission housing from a fabrication to a magnesium casting reduced cost and scrap rate.


tion, post-casting operations and tooling costs should be considered to obtain a quality, low-cost component.


• Magnesium has a high stiffness- to-weight ratio. This characteris- tic is important where resistance to defl ection is desired in a lightweight component.


• Unlike molten aluminum, molten magnesium does not react with tool steels, resulting in longer die life and increased productiv- ity. Because of low erosion and heat input, which reduce the propensity for thermal fatigue, magnesium can achieve three to four times the die life than can be achieved with aluminum.


PROCESSING CONSIDERATIONS • 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 require- ments for machining magnesium alloys permit the use of deeper cuts and higher feed rates, thus permitting fast and effi cient ma- chining when compared to other metals. Magnesium alloys also normally produce well-broken chips, which are easy to handle.


• Annealing, artifi cial-aging or stress-relieving treatments normally are not necessary to achieve stable fi nal dimensions.


36 | METAL CASTING DESIGN & PURCHASING | Jul/Aug 2012


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