Microstructure and Properties of Elektron 21 Magnesium Alloy.

Abstract

Magnesium is the lightest of metals used for constructional alloys. These alloys are characterised by low density and good mechanical properties (Mordike et al., 2001), however they are showed poor properties in elevated temperature (Mordike, 2002). Among various magnesium alloys, rare earth containing alloys are known to show good mechanical properties and excellent creep resistance (Avedesian et al., 1994). Mainly for these reasons, magnesium alloys have a widespread application in the motor vehicle and aircraft industries. The disadvantages are poor properties in elevated temperatures and high reactivity (Mordike, 2001). A range of alloys are commercially available from Mg-Al alloys to highest strength, high temperature Mg-Zr alloys with addition of yttrium. However alloys that contain yttrium have high associated cost due the difficulties in casting. Therefore there is a need for an alternative alloy which has similar properties to Mg-Y alloys, but with foundry handling and associated costs like non-yttrium containing alloys (Lorimer et al., 2003). Magnesium alloys containing neodymium and gadolinium are interesting as light structural materials with high mechanical properties at room and elevated temperatures (Smola et al., 2002). Mg-Nd-Gd-Zr magnesium alloys are characterised by high-strength and good creep resistance to automotive and aerospace applications (Rokhlin et al., 1996). The rare earth elements have beneficial effect of on the creep properties, thermal stability of structure and mechanical properties of magnesium alloys (He et al., 2006). Elektron 21 is new magnesium based casting alloy containing neodymium, gadolinium and zinc for used to approximately 200°C. This alloy has high strength, good corrosion resistance and excellent castability. Neodymium has a positive effect on tensile strength at elevated temperature, reduces porosity of casts and susceptibility to cracking during welding. Gadolinium, like neodymium shows a decreasing solid solubility as temperature falls, indicating potential for precipitation strengthening. Addition neodymium to Mg-Gd alloys reduces the solid solubility of gadolinium. It improves precipitation hardening response, at lower levels of gadolinium than the binary system offers. Zinc is added to magnesium alloys in sufficient quantities to achieve precipitation strengthening. It improves strength without reducing ductility. Zirconium, which does not form any phases with magnesium or alloying elements, contributes to the obtaining of a fine grain structure and improves the mechanical properties at an ambient temperature, castability and corrosion performance. Elektron 21 is being used in both civil and military aircraft and also in automobile (motorsport) industry (Lyon et al., 2005).