Study On The Preparation And The Microstructure And Mechanical Properties Of Mg-3Al-0.5SiO₂ Composite Materials With Sn Modification

Magnesium and its alloys have been widely used in automobiles,aerospace and electronic products in recent years due to their low density,high specific strength,specific stiffness,good conductivity and excellent damping and shock absorption properties.Particle reinforced magnesium alloys have become a research focus in recent years.In-situ particle reinforced magnesium alloys have attracted much attention of many studies because of its good interface with the matrix.On the basis of in-situ particle reinforced AS-based magnesium alloys,nano-SiO₂ powder is used to replace Si element,Mg₂Si strengthening phase is introduced,and Sn element is added to study the modification mechanism on Mg₂Si phase.Combining with plastic deformation process,the effect of strengthening phase on microstructure and mechanical properties is discussed in order to provide an experimental basis for developing an excellent performance and low cost new magnesium alloys.In this paper,the Sn content of Mg-3Al-0.5SiO₂-xSn composites with 0%,1%,3%,5%,7%and 10%were prepared by traditional casting method.Then the as-cast composites were treated by solid solution at 425?,24h and aging at425?,24h+180?,16h,respectively.Then hot extrusion was done through aging.Microstructure and phase of as-cast,heat-treated and extruded composites were analyzed by optical microscopy?OM?,scanning electron microscopy?SEM?,energy dispersive spectroscopy?EDS?,transmission electron microscopy?TEM?and X-ray diffraction?XRD?.Room tensile tests and hardness tests of as-cast and as-extruded composites were carried out by electronic universal testing machine and hardness-testing device in order to analyze variation of mechanical properties.Finally the refinement mechanism and strengthening mechanism were discussed.The results show that the addition of nano-SiO₂ powder introduces a new spinel phase MgAl₂O₄ with high strength and high hardness.With the increase of Sn content,the Mg₂Si phase undergoes the following changes:Mg₂Si?Mg₂(Si_x Sn_1-x)?Mg₂Sn.The matrix grains of as-cast and as-extruded composites decrease first and then increase with the increase of Sn content.With the increase of Sn mass fraction,the tensile strength of as-cast composites increases first and then decreases but the tensile strength and yield strength of as-extruded composites have been increasing.Fine grain strengthening and second phase strengthening are the main reasons for the improvement of mechanical properties of composites.