In this article, mechanical and electromagnetic stirring methods were employed in different sequences during the stir casting process in order to fabricate metal matrix nanocomposite. Sequence of stirring methods can affect particle distribution and porosity of the composite and consequently alter microstructural and mechanical properties. To investigate the stirring effects, AZ31B/1.5 vol% nano-Al2O3 composites were produced using different stirring processes. Next, the as-cast billets were hot-extruded at 350 °C using 20:1 extrusion ratio. The results showed that the sequence of the mechanical and electromagnetic stirring methods have considerable effects on porosity, grain size, microhardness, tensile properties, and high cycle fatigue behavior of the composites. The best mechanical and microstructural properties were obtained by the mechanical stirring method followed by the electromagnetic stirring. The samples produced by this method exhibited 44.7% decrease in grain size, 40.8% increase in hardness, 12.3% enhancement in ultimate tensile strength, and 16.5% improvement in maximum elongation, compared to the monolithic AZ31B sample. Additionally, the endurance limit of the composite enhanced about 21% in high cycle fatigue regime. On the other hand, nanocomposite fabricated by mechanical stirring method showed the poorest behavior under cyclic loading.
magnesium metal matrix composite stir casting mechanical stirring electromagnetic stirring high cycle fatigue
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The authors would like to thank Mr. Arash Shafiee Sabet for his kind help during the experiments.