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Magnesium Alloys


high strengths at light weights. Magnesium possesses proper- ties that can open the door to structural applications and has gained widespread use in automo- tive components. Non-automotive applications, spurred on by the computer, electronics and power tool industries, continue to expand.


C Magnesium has a density


two-thirds that of aluminum and slightly higher than that of fi ber-reinforced plastics while maintaining the mechanical and physical properties shown in Tables 1-2. When coupled with the inherent advantages of the metalcasting process, magnesium alloys can yield cost-eff ective solutions to product needs by allowing for part consolidation and weight savings over other materials and manufacturing methods. Magnesium can be cast in a variety


This structural automotive liftgate met the same crash requirements as a steel alternative.


of methods, including high-pressure di- ecasting, permanent mold casting, sand casting, and semi-solid and squeeze casting. Diff erent alloys may be specifi ed for these diff erent processes, but in cases where the same alloy is used with dif- ferent casting processes, the properties


Table 1. Typical Mechanical Properties of Magnesium at Room Temperature Property


Ultimate Tensile Strength MPa


Tensile Yield Strength (0.2% offset )


225 210 190 215 MPa


Compressive Yield Strength MPa Fracture Elongation


Elastic Modulus, tension Elastic Modulus, shear Brinell Hardness


Impact Strength, Charpy un-notched test bars


GPa GPa


J


(250) 160


(160) 160


% 3 (7)


45 17


70 6


(9)


(240) 130


(130) 130 8


(13) 45 17


65 17


(18)


(230) 125


(125) 125 10


(15) 45 17


60 18


(18)


(210) 90


(90)


(20) 45 17


45 18


(18)


(240) 140


(140)


90 140 12


6


(15) 45 17


(16)


ast magnesium alloys have gained popularity in recent years due to their ability to maintain


of the fi nished castings will de- pend on the method. T e most prevalent casting method for magnesium is diecasting. In this process, complex, thin-walled parts are produced at high production rates aided by the low-heat content per volume of molten metal. Both hot cham- ber and cold chamber machines can be used for magnesium. For optimum performance, it is recommended that higher shot speeds are used for magne- sium compared to aluminum, especially for thin-walled parts. Diecasting process variants (such as vacuum diecasting) can produce components with lower


porosity and better properties than standard diecasting. Magnesium also is conducive to


semi-solid casting methods, typically with magnesium alloy granules or partially solidifi ed alloys rather than liquid magnesium. Semi-solid molding commonly is used for smaller parts, such as those used in the electronics industry.


Properties Because of their properties, mag-


Unit AZ91 AM60 AM50 AM20 AS41 AS21 AE42 240


175


(220) 110


(120) 110 9


(13) 45 17


60 55 4


5 (12) Note: Values in parentheses show mean property values obtained from separately diecast test bars.


Table 2. Typical Physical Properties of Magnesium Property


Density Liquidus Temperature


Incipient Melting Temperature


Linear Thermal Expansion Coeffi cient


1.81 1.8 F F7 1,110 µm/m 68-212 26


Specifi c Heat of Fusion kJ/kg Specifi c Heat


kJ/kg*K 68


Thermal Conductivity W/K*m 68 Electrical Conductivity MS/m 68


230


(230) 145


(145) 145 10


(11) 45 17


60 5


(12)


Unit Temp (F) AZ91 AM60 AM50 AM20 AS41 AS21 AE42 g/cu cm 68


1.77 1.75 1.77 1.76 1.79 1,139 1,148 1,182 1,144 1,169 1,157 788-815 788-815 788-815 788-815 788-815 788-815 1094 26 26 26 26.1 26.1 26.1


370 370 370 370 370 370 370 1.02 1.02 1.02 1.02 1.02 1.02 1.02 51


61 6.6 nm 38 METAL CASTING DESIGN & PURCHASING


65 9.1


94 68 84 13.1 nm 10.8


84 11.7


nesium alloys can provide a casting designer with several advantages over other lightweight alloys: • Weight—T e lightest of all structural metals, magnesium preserves the light weight of a design without sacrifi cing strength and rigidity (Fig. 1). T is benefi t 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 equip- ment continue to take advantage of magnesium’s low density in expand- ing 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 pro- vides for quieter operation of equip- ment when magnesium castings are


2013 CASTING SOURCE DIRECTORY


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