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 α-Mg and β-Mg17Al12 phases. However, the other two precipitates (Al11Sm3 and Al2Sm) were observed along grain boundaries in the alloys containing Sm. The amount of Al11Sm3 and Al2Sm precipitates was increased with the increment of Sm content. Meanwhile, volume fraction of β-Mg17Al12 phase was decreased. Moreover, the morphology of β-Mg17Al12 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 °C. Compared with ultimate tensile strength (UTS), yield strength (YS) and elongation (ɛ) of Mg–5Al–0.3Mn alloy, UTS, YS and ɛ 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 °C, respectively. The improvement of tensile properties was attributed to the decreased amount of β-Mg17Al12 and its refined morphology, and high thermal stable Al11Sm3 and Al2Sm precipitates which effectively prohibited dislocation movement and grain boundary sliding during deformation process.

Research highlights
► Mg–5Al–0.3Mn–xSm alloys were prepared by metal mould casting method.
► Effects of Sm on the microstructures and tensile properties were investigated.
► Al11Sm3 and Al2Sm precipitates were formed and their amount increased with increasing Sm content.
► Volume fraction of β-Mg17Al12 phase was decreased and its morphology was refined.
► Mg–5Al–0.3Mn–2Sm alloy exhibited the highest tensile strength and ductility.