Effects of Li addition on microstructure and mechanical properties of Mg-6Al-2Sn-0.4Mn alloys

Effects of Li addition (2%, 5%, 8% and 11%) on microstructure and mechanical properties of the as-cast and as-extruded Mg-6Al-2Sn-0.4Mn-based alloys were investigated. Mg-xLi-6Al-2Sn-0.4Mn (x=2, 5, 8 and 11, mass fraction, %) alloys were cast under an SF6 and CO2 atmosphere at 700 degrees C. After homogenization heat treatment at 350 degrees C, cast billets were extruded with a reduction ratio of 40: 1 at 200 degrees C. Li addition to Mg-6Al-2Sn-0.4Mn resulted in the formation of MgSnLi2 and MgAlLi2 and/or AlLi intermetallic compounds and random basal texture. With increasing Li addition, beta-Li phase was increased and the average area fraction of precipitates increased. Compression yield strength was increased from 212 to 235, 242 and 239 MPa as Li content was increased from 2% to 5%, 8% and 11%, respectively. Elongation was remarkably increased above 60% in 11% Li alloy. It is probable that Li-containing phases play a significant role in the enhanced mechanical properties by Li addition.