Study On Fabrication And Wear Behavior Of Mg₂Si,SiC_p Hybrid Reinforced Magnesium Matrix Composites

Magnesium resources are rich both in the crust and sea water,and Magnesium is thelightest one in the Common metal,Its density is only 1.74g/cm³, the 1/4 times of the densityof iron, the 2/3 times of the density of aluminum. At the same time, as the green projectmaterials in the 21st century, magnesium also has the advantages which other metals do nothave: high specific strength and specific stiffness, denoise and decreasing vibration,recyclable, easy processing, non-toxic, non-magnetic and so on. Now magnesium inaerospace, electronics, optical equipment manufacturing, defense and other fields have beengot a certain application, especially in the automobile industry.However, magnesium and magnesium alloys has poor performance in strength,toughness, creep resistance, many researchers do a lot of research on how to improve theperformance of magnesium alloys, including particulate reinforced magnesium matrixcomposites. The study shows that the magnesium matrix composites have better mechanicaland physical properties, so the magnesium matrix composites have more future.In recent years, more and more researchers have studied about SiC, Mg₂Si or otherparticulate reinforced magnesium matrix composites, but the hybrid reinforced magnesiummatrix composites are relatively few. Therefore, to improve the mechanical properties ofcomposite materials at the same time to study the fracture mechanism and the wearperformance will accelerate the process in actually use, with far-reaching significance.Magnesium-based metal matrix composites (MMCs) reinforced by in-situ Mg₂Siparticles were successfully fabricated. Then SiC particles were added into the composite bythe way of stirring-melt casting process after the SiC particles had been pretreated. So thisMagnesium-based metal matrix composite is reinforced by both Mg₂Si and SiC particles.The best fabrication parameters are obtained though the studying of the(Mg₂Si+SiC_p)/Mgcomposites prepared at different stirring speeds ,different stirring time and by whetheradding pretreated SiC_p. The experiment results show that for stirring-melt casting processthe best stirring speed is 500r/min and the best stirring time is 30min, and the SiC_p particlesshould be pretreated at the temperature of 600℃for two hours.By calculating the latticemismatch between Mg₂Si and SiC in the(Mg₂Si+SiC_p)/Mg composites, the minimum latticemismatch was found between the [1210] face of SiC and the [001] face of Mg₂Si. It is only3.035%. So the primacyα-Mg₂Si may choose the face of SiC_p as the substrate ofnon-homogeneous nucleation.After analyzing the scanning electron microscope image, it was discovered that SiC_p isinserted in the Mg₂Si phase. This proved that the primacyα-Mg₂Si phase growth on thesurface of SiC_p. Thus the grain is reinforced and the property of the composite is enhanced.Through the data got from the tensile test machine,the tensile strength and percentelongation can be obtained. The results show that the tensile strength of the composite without Mg₂Si and SiC_p particles is 35.67MPa, and the percent elongation is 2.29%. And thetensile strength of the composite reinforced by Mg₂Si and SiC_p particles measure up to82.15Mpa, and its percent elongation reach to 3.15%. The percent tensile strength andelongation are respectively improved by 130% and 37.65%.The composite reinforced byMg₂Si+10vol.%SiC_p particles has greater tensile strength. Its tensile strength reached to91.98Mpa, and the percent elongation reach to 3.38%. Compared with pure magnesium, thepercent of tensile strength and elongation are respectively improved by 157.86% and 47.60%.The fracture mechanics has been discussed after analyzing the features of the fracture. Onthe surface of the fracture of pure magnesium a great many cleavage planes and stages canbe discovered. So the mechanic of fracture of pure magnesium is transgranular fracture. TheVolume of Mg₂Si produced in the Mg₂Si/Mg composite is relatively small, so the mainmechanic of fracture is still the cleavage fracture. But the mechanic has changed when SiC_pparticles were added into the magnesium-based matrix composite. Both the torn edge andcleavage planes existed on the surface of fracture. Some second-phase particles existed hasbeen discovered in some dimples. After analyzing the high magnification fractograph, it wasfound that microvoids between the interface of SiC_p and matrix have been observed andsome SiC_p dissociated from the matrix. When the composite was applied tensile stress, thecrack initiates at the interface of SiC_p and matrix. Especially the crack initiates at the placewhere the particles agglomerate more easily. As the deformation continues, the crackpropagation is going along the grain boundaries. When some cracks coalesce, intergranularoccurs. Sometime second-phase particles would be pulled out from the matrix. That istypically brittle.All composite material samples are performed abrasive wear test in different sizesandpaper and different load, according to the wear weight loss curve and scanning electronmicroscope image of the surface,wear mechanism was discussed. Under the same load, themore the enhanced particle, the less the Mg composites wear weightlessness, the higher theabrasive resistance. The more the content of particle, the higher the abrasive resistance is.Through the analysis of the wear surface morphology, study finds that the more the particlethe less the spalling pits of composite wear surface, which is because in the process ofwearing, composite particle load by enhanced particle, so adhesive wear becomes weak andimproves the wear resistance of composite materials.This paper also studied the affect of miscrostructures and mechanical properties about(Mg₂Si+SiC_p)/Mg composite materials by hot extrusion, from the microstructure photos wecan get to know that hot extrusion can making the particle break , increasing the quantity ofreinforcement phase , refining the partical size . It also can reduce the porosity of compositematerials, increasing the interface strength, more uniform the particle distribution thanbefore . In this study the ingot of(Mg₂Si+SiC_p)/Mg based Composite materials is preheatedat 420℃,approximately 2 hours , extruded at 400℃. The study found that hot extruded(Mg₂Si+SiC_p)/Mg have an improvement than casting materials in hardness, tensile strength, elongation and wear of based composite materials.