Preparation And Study On Microstructure And Properties Of In-situ Mg₂Sn Reinforced Magnesium Matrix Composites

Particle reinforced magnesium matrix composite is a hot research topic in recent years.It has the characteristics of simple preparation process,suitable for machining and so on.At the same time,it has some advantages in mechanical properties,and is suitable for large-scale production.In situ method,as an enhanced method of magnesium matrix composites,can enhance the phase formation in-situ.Meanwhile,the utility model has the advantages of no pollution,good thermal stability,good compatibility with the substrate,low preparation cost,etc.It has become an important direction for the development and preparation of high performance magnesium matrix composites.In this paper,choosing pure Mg as the matrix,in situ synthesis of Mg2 Sn nanoparticles in the matrix by mechanical alloying.The magnesium matrix composite material made of composite powder was prepared by hot pressing sintering method.The influence of the mechanical alloying time and the size of Sn particle on the microstructure and mechanical properties of the composite were studied using XRD,optical microscopy,SEM,TEM,DSC and the compression experiments at room temperature and the phase transformation in the process of hot press sintering were analyzed.The main conclusions are as follows:Mechanical alloying can produce Mg2 Sn particles in Mg powder and nano Sn powder in situ and the amount of Mg2 Sn phase increases with the raise of mechanical alloying time.Sn particles could be completely transformed into Mg2 Sn by enough mechanical alloying time.At the same time,the morphology of Mg2 Sn clusters changed constantly.When the mechanical alloying time increased from 5h to 20 h,the Mg2 Sn in the matrix changed from continuous lamellar to granular,and the distribution in the matrix was more uniform.The particle size of Mg2 Sn nanocrystals decreases with the increase of mechanical alloying time and the hardness and compressive properties of the composites are enhanced at the same time.After mechanical alloying 20 h,the size of Mg2 Sn particles is about 30 nm,the microhardness of the particles can reach 210 HV,the compressive strength is 406 MPa,the yield strength is273 MPa,the fracture strain is 11%.After the nano Sn powder was changed into micron Sn powder,the mechanical alloying could also produce Mg2 Sn.However,compared with the nano Sn powder,the reaction rate of mechanical alloying is obviously reduced and it takes longer mechanical alloying for thereaction to begin.The size of the Mg2 Sn clusters is larger,and the layer is continuous in the matrix.The hardness and compressive properties of the composites after hot pressing sintering were also increased with the increase of mechanical alloying time.However,compared with the composites made of nano Sn powder,the mechanical properties of the composites with the same mechanical alloying time were about 50% less than that of the composites.During the heating process,the residual Sn phase of the powder will continue to react with Mg after melting,forming the Mg2 Sn phase.When the concentration of Sn in the powder is high,the eutectic will be produced in the microstructure.The Mg2 Sn phase will be gradually refined with the increase of temperature and more uniform distribution in the composites.