Magnesium has a close-packed hexagonal lattice elongated along the six-fold axis with a c/a ratio of 1.856. Its melting point is 649°C and its density is 1.74 g cm−3. It has specialized applications in engineering by virtue of its useful properties and characteristics. It is the lightest of the common engineering metals, and when applied with discrimination it resists corrosion well. Its mechanical properties are useful but are usually improved by alloying. Other attributes that attract special applications include easy machinability, stiffness, high strength-to-weight ratio and low neutron capture cross section. The compositions and properties of some representative alloys are given in Table 14.1.