Effect of Sm content on microstructure evolution and mechanical properties of as-cast Mg−6Al−2Sr alloys

Abstract

Mg−6Al−2Sr alloys with different Sm contents (0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg−6Al−2Sr alloys were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, X-ray diffraction and tensile test. The results show that the microstructure of as-cast Mg−6Al−2Sr alloy is composed of α-Mg, Mg₁₇Al₁₂, Mg₁₃Al₃Sr and lamellar acicular Al₄Sr phase. After adding Sm element, granular block Al₂Sm phase appears in the grain. With the increase of Sm content, the discontinuous long strip reticular Mg₁₇Al₁₂ phase and the lamellar acicular Al₄Sr phase gradually decrease, and the Al₂Sm phase increases and distributes more dispersedly, so the alloy microstructure is continuously refined. The average grain size of the alloys decreases at first and then increases with the increase of Sm content. When the Sm content is 1.5 wt%, the average grain size reaches the minimum value of 94.6 µm. With the increase of Sm content, the mechanical properties of the alloy at room temperature first increase and then decrease. When the Sm content is 1.5 wt%, the alloy has the best comprehensive mechanical properties at room temperature.

Keywords

Mg−6Al−2Sr alloy / Sm / mechanical properties / microstructure / Al₂Sm phase

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