Microstructures,Mechanical Properties And Multiphase Interaction Of N-SiCp Reinforced Mg-Al-Si Matrix Composites Processed By ECAP

Mg-9Al-1Si-XSiC magnesium matrix composites fabricated by semisolid stirring assisted ultrasonic vibration were subjected to equal channel angular pressing?ECAP?.Optical microscopy?OM?,X-ray diffractometer?XRD?,scanning electron microscopy?SEM?and Energy dispersive spectrometer?EDS?were employed to observe the microstructures of as-cast and ECAPed composites.The evolution of microstructure during ECAP was also investigated.The mechanical properties of as-cast and ECAPed composites were measured by electronic universal testing machine at room temperature and 200?.The results showed that most of the n-SiCp were evenly dispersed in the matrix with few SiC agglomeration and segregation in the composites.However,the amount of SiC agglomeration increased with the mass fraction of n-SiCp increasing.The matrix grains in the Mg-9Al-1Si-XSiC composites were refined gradually with the increasing of n-SiCp,leading to the Hall-Petch strengthening effect.The dispersed n-SiCp not only refined the coarse ?-Mg₁₇Al₁₂ and Mg₂ Si,but also facilitated the precipitation of ?-Mg₁₇Al₁₂ lamellaes.The mechanical properties including ultimate tensile strength,yield strength and elongationpresented a decline before an increase trend and Mg-9Al-1Si-1SiC showed the best values.Comparing with as-cast composites,the size of matrix grains,?-Mg₁₇Al₁₂ and Mg₂Si phase in Mg-9Al-1Si-1SiC composites decreased remarkably after different passes ECAP process.The brokenlevels of ?-Mg₁₇Al₁₂ and Mg₂ Si phase increased obviously and the distribution of crushed particles became much more uniform as ECAP passes increasing.Some of the matrix grains in Mg-9Al-1Si-1SiC grew slightly after two and three passes ECAP comparing with one pass ECAPed Mg-9Al-1Si-1SiC composites.Besides,the mechanical properties of ECAPed Mg-9Al-1Si-1SiC at room temperature and 200? were significantly improved.At room temperature,the ultimate tensile strength increased slightly as ECAP passes increasing;the fracture elongation reduced firstly after 2 and 3 passes ECAP then increased obviously after 4 passes ECAP.At 200 ?,ultimate tensile strength and elongation improved gradually.The largest values of ultimate tensile strength and elongation of Mg-9Al-1Si-1SiC at room temperature and 200?are both obtained after four pass ECAP.Comparing the microstructures and mechanical properties of Mg-9Al-1Si,Mg-9Al-1SiC and Mg-9Al-1Si-1SiC composites after four passes ECAP,the following conclusions could be drawn.The crushing effect of Mg₂ Si phase and?-Mg₁₇Al₁₂ in composites and the distribution of crashed particles during ECAP could be modified by introducing of n-SiCp.The effect of n-SiCp and Mg₂ Si particles on grain refinement of matrix was different during ECAP.The matrixgrain size of Mg-9Al-1Si-1SiC was smallest followed by Mg-9Al-1SiC,and Mg-9Al-1Si was the largest.Besides ?-Mg₁₇Al₁₂ pashe,there are also two other kinds of reinforcements n-SiCp and Mg₂ Si with large mass fractions in Mg-9Al-1Si-1SiC composites.The distribution of the reinforcements in the composites is modified by ECAP process which results in the improvement of mechanical properties obviously.Therefore,both the ultimate tensile strength and elongation of Mg-9Al-1Si-1SiC were larger than that of Mg-9Al-1Si and Mg-9Al-1SiC.