Formaton of nanocrystalline Mg 2Si and Mg 2Si dispersion strengthened Mg-Al alloy by mechanical alloying

Abstract

Formation of Mg 2Si via mechanical alloying of elemental Mg and Si powders has been investigated. The formation of Mg 2Si occurs after 10 hours of mechanical alloying. Nanocrystalline structure of Mg 2Si with grain size of 22 nm obtained after 50 hours of milling was found to be stable upon heating to about 390 °C. Sudden increase in crystalline size to 157 nm after annealing at 520 °C was observed. Although the reaction between Mg and Si could be completed after about 50 hours of mechanical alloying, thermal assisted reaction starting at as low as 190 °C could promote the formation of Mg 2Si at a short milling duration and hence reduce Fe contamination. Mg-Al alloy reinforced by Mg 2Si was prepared by milling Mg, Si and Al powders. Intermediate phase of Al 12Mg 17 has been detected after 5 hours of mechanical alloying. This intermediate phase was observed to disappear to form equilibrium solid solution of Mg-Al alloy after annealing at 300 °C.