The Mechanical Properties of Magnesium Alloy Alloys

Magnesium alloys are used in a wide range of applications, including cladding fuel rods in nuclear power reactors. The optimum magnesium content for cladding purposes is 80%-90% magnesium with a maximum aluminium content of 10-12 wt.%, although other Al content ranges are possible.

The mechanical properties of cast and wrought Mg alloys are very similar to those of aluminum. The tensile strength is largely the same as in aluminum, and the modulus of elasticity is also very similar to that of pure aluminium for alloys up to 5 wt.% magnesium; however, it is generally lower at higher Mg contents.

Fatigue resistance increases with increasing magnesium content. This is because, unlike in aluminum, magnesium atoms are not able to disperse easily and remain in the matrix throughout the entire length of the specimen.

Corrosion resistant behaviour of cast Mg-Al-RE alloys is usually improved by the addition of alloying elements such as chromium, nickel, copper, titanium and molybdenum. These additions do not affect the ductility, creep and heat resistance of these alloys; however, they may influence the microstructure and surface quality of the alloy, thereby decreasing the corrosion resistance.

Despite the increased magnesium content, these alloys are not particularly easy to cast. The optimum fluidity of the melt is usually achieved at around 4 wt.% Al, although mischmetal can be added to improve the machinability of these alloys.

In addition, the microstructures of these alloys are affected by cooling rate, as shown in Table 3. For both investigated alloys the solid fraction at the dendrite coherency point determined from the second derivative of the cooling curve increases with an increase in Mg content and cooling rate.