Effects of samarium on microstructures and tensile properties of Mg-5Al-0.3Mn alloy

Microstructures and tensile properties of Mg-5Al-0.3Mn-xSm (x = 0, 1, 2 and 3 wt.%) alloys prepared by metal mould casting method were investigated. It was demonstrated that Mg-5Al-0.3Mn alloy was mainly composed of alpha-Mg and beta-Mg(17)Al(12) phases. However, the other two precipitates (Al(11)Sm(3) and Al(2)Sm) were observed along grain boundaries in the alloys containing Sm. The amount of Al(11)Sm(3) and Al(2)Sm precipitates was increased with the increment of Sm content. Meanwhile, volume fraction of beta-Mg(17)Al(12) phase was decreased. Moreover, the morphology of (beta-Mg(17)Al(12) was altered from bulk bone-like shape to spherical one. Tensile results showed that Mg-5Al-0.3Mn-2Sm alloy exhibited the highest tensile properties both at room temperature and 150 degrees C. Compared with ultimate tensile strength (UTS), yield strength (YS) and elongation (epsilon) of Mg-5Al-0.3Mn alloy, UTS, YS and e of Mg-5Al-0.3Mn-2Sm alloy were enhanced by 30%, 45% and 35% at room temperature, and by 17,%, 48% and 96% at 150 degrees C, respectively. The improvement of tensile properties was attributed to the decreased amount of beta-Mg(17)Al(12) and its refined morphology, and high thermal stable Al(11)Sm(3) and Al(2)Sm precipitates which effectively prohibited dislocation movement and grain boundary sliding during deformation process. (C) 2011 Elsevier B.V. All rights reserved