Study On The Structure And Properties Of SiC/Mg-based Composites Prepared By SPS Method

In this paper,pure magnesium is used as the matrix material,and nano-sized SiC powder is used as the reinforcement particles.The spark plasma sintering method is used to prepare x% SiC/Mg-based composite materials（x=1,3,5,10,15）.The microstructure and metallographic morphology of the made SiC/Mg composite material were characterized,and used compression tests to analyze the mechanical properties of SiC/Mg composites.The influence of the introduction of nano-sized SiC reinforcement particles on the structure and mechanical properties of the material is discussed.At the same time,we also conducted thermal simulation tests on SiC/Mg composites,and systematically studied the influence of deformation rate and deformation temperature on the microstructure and mechanical properties of SiC/Mg composites.Combining the two analytical methods of constitutive equation and thermal processing diagram,the microstructure change,deformation mechanism of SiC/Mg composite material in high temperature deformation and the suitable processing range in actual thermal processing are discussed.The processing performance and thermal stability of the material were explored and tested.The test results show that most of the added SiC reinforcement particles are located at the grain boundaries of the SiC/Mg composite,and only a few SiC reinforcement particles are distributed inside the grains.As the SiC content increases from 1%to 15%,the reinforcement gradually fills up the grain boundaries and begins to agglomerate,and agglomerations are more likely to occur at the junctions of polycrystalline grains.The introduction of SiC reinforcement particles has a significant impact on the mechanical properties of SiC/Mg composites.In terms of microhardness,the addition of SiC significantly enhances the hardness of SiC/Mg composites.In terms of compressibility,the influence of the addition of SiC reinforcement on the mechanical properties is divided into two stages.When the addition of SiC is less than 5%,the compressive strength and yield strength of SiC/Mg composites are lower than those of pure magnesium sintered samples.When the addition amount of SiC is higher than 5%,the compressive strength and yield strength of SiC/Mg composites are significantly improved.After the SiC/Mg composite material undergoes a hot compression test,the metallographic structure changes greatly with the change of deformation temperature and deformation rate.Under the processing conditions of low deformation temperature and high deformation rate,the structure of SiC/Mg composite material still maintains the morphology after sintering,and its morphology is that a few grains are elongated.With the increase of the deformation temperature and the compression of the low strain rate,the SiC/Mg composite material will undergo a dynamic recrystallization process during thermal deformation,and a large number of dynamic recrystallized grains will be formed inside the material.The stress-strain curve can also better prove this conclusion.In the state of low deformation temperature and high strain rate,the material will not appear rheological steady state stage.The SiC/Mg composite material will fracture before the work hardening and recrystallization softening reach equilibrium.Under the condition of high strain temperature and low strain rate,dynamic recrystallization process occurs inside the material.When the internal recrystallization softening and work hardening of the material reach a dynamic balance,the SiC/Mg composite material will produce recrystallized grains.Combined with the thermal simulation test data,we calculate that the compression deformation rheological behavior of SiC/Mg composites can establish the following constitutive equation model,which can be described by the Arrhenius relationship modified by the hyperbolic sine function and the Z parameter,respectively:5%SiC/Mg:(5=6.2×10⁶[sinh?（0.022321）]^11.1exp?（-106150/）10%SiC/Mg:(5=4×10⁷[sinh?（0.020794）]^10.6exp?（-122150/）Based on the thermal simulation test data and the Prasad instability criterion,the thermal processing map of the SiC/Mg composite is established.Through the analysis of the thermal processing map,it is determined that the processing range of the SiC/Mg composite is at the deformation temperature of 450℃～500℃,The strain rate is in the interval of 0.001 s^-1～0.01 s^-1,and the power dissipation coefficient of the SiC/Mg composite is at its peak in this interval.The rheological instability zone of the material is located in the range of deformation temperature 400℃～500℃and strain rate 0.1s^-1～1 s^-1.The structure of SiC/Mg composites processed in this region is prone to cracks.After friction stir processing,the deformation zone of the SiC/Mg composite material has a clearer division of WNZ,TMAZ and SAZ.The WNZ zone is a complete dynamic recrystallized grain with a grain size of 500 nm.The agglomeration of SiC particles basically disappears.Most of the TMAZ area is dynamically recrystallized grains,but there are still a few elongated streamline grains,and the agglomeration phenomenon is improved.In terms of mechanical properties,the Vickers hardness of the deformed area of the SiC/Mg composite material is significantly higher than that of the base material,and the Vickers hardness of the WNZ zone is as high as 72～75HV.The thermal compression material is subjected to annealing test to observe the structure after annealing.The test shows that the SiC/Mg composite material itself has excellent thermal stability due to the addition of SiC particles.