Study On The Preparation And The Strengthening Mechanism Of Differential Temperature Extrusion For X%SiC/AZ91D Composite Materials

Magnesium matrix composites are used to improve the mechanical properties of magnesium alloys due to their low density,therefore,it has a wide range of applications in the field of automotive and aerospace.Compared with other types of magnesium matrix composites,Magnesium matrix composites with particles reinforcement has gained widely attention because of its lower production costs and easier fabrication machinability.When SPD is applied to magnesium matrix composites,their microstructures can be refined,and the mechanical properties would improve due to the refinement of the microstructure.There is an un-homogeneous microstructure of composite materials when using original extrusion,the re-dispersion effect of reinforcement particles in magnesium matrix composites are not satisfactory,and it is detrimental to the popularization of Magnesium Matrix Composites.In this paper,the magnesium matrix composites were prepared by semi-solid stirring method when using the AZ91 D alloy as matrix,the SiC nanoparticles with 50 nm average size as reinforcement particals,and then it was extruded by differential temperature extrusion.It was found that the smaller size the reinforcement particle is,the more significant improvement the mechanical properties of the composites are.During the differential temperature extrusion.Because of the heat conduction effect,the extruded ingot was always in the state of temperature difference,it will have an important influence on the microstructure,mechanical properties and redispersion effect of nano SiC particles in the composites.The microstructure,mechanical properties,fracture appearance and microhardness of the as-cast and as-extruded x%SiC/AZ91 D composites were analyzed to indicate the refining mechanism and strengthening mechanism.The results indicated that the microstructure of the x%SiC/AZ91 D composites were finer with the increasing content of SiC particle.Compared with original extrusion deformation,the re-dispersion of nano-SiC particles were fine via the differential temperature extrusion,and the microstructure is fine and uniform.Nevertheless,the mechanical properties were increased first and then decreased.Under the optimized conditions,the tensile strength is 315 MPa,the yield strength is 200 MPa,and the elongation is 10.3%.