Abstract Magnesium is the lightest of all metals used as the basis for constructional alloys. It is this property which entices automobile manufacturers to replace denser materials, not only steels, cast irons and copper base alloys but even aluminium alloys by magnesium based alloys. The requirement to reduce the weight of car components as a result in part of the introduction of legislation limiting emission has triggered renewed interest in magnesium. The growth rate over the next 10 years has been forecast to be 7% per annum.(Fig. 1) A wider use of magnesium base alloys necessitates several parallel programs. These can be classified as alloy development, process development:improvement and design considerations. These will be discussed briefly and followed by some examples of the increasing uses of magnesium and future trends. Magnesium and magnesium alloys are primarily used in aeronautical and automobile industry in wide variety of structural characteristics because of their favorable combination of tensile strength (160 to 365 MPa), elastic modulus (45 GPa), and low density (1 740 kg/m3), which is two-thirds that of aluminum). Magnesium alloys have high strength-to-weight ratio (tensile strength/density), comparable to those of other structural metals [1-4] Knowledge of the relaxation properties of metal materials at elevated temperatures is necessary for the verification of susceptibility of castings to the creation of defects during the production and forming processes. Temperature limits of materials where highest tension values are generated may be detected with tensile tests under high temperatures.