Fabrication,Microstructures And Mechanical Properties Of SiC_p Reinforced Magnesium Matrix Clad Plate

In this paper,AZ91 alloy was used as matrix and SiC_p was used as reinforcement.The particulate reinforced magnesium matrix composite?PMMCs?with volume fraction of 10%was fabricated by semi-solid stir casting,the AZ91/PMMCs clad plate with thickness of 2 mm was fabricated by extrusion process.And then the clad plate was rolled to 1mm at 350^oC.The effect of extrusion temperature and solution pretreatment on the microstructure and mechanical properties of the clad plate was studied.The microstructures and mechanical properties of AZ91/PMMCs clad plate after rolling were analyzed,and the effect of thickness ratio on the microstructures and mechanical properties of rolled AZ91/PMMCs clad plate was investigated.The results show that the AZ91/PMMCs clad plates with good interface bonding were successfully fabricated by extrusion.Complete dynamic recrystallization?DRX?took place in composite layer and alloy layer.The grain size of the inner alloy is smaller than that of the outer alloy,and the grain size of composite layer is obviously smaller than that of alloy layer.The microhardness of the inner alloy is higher than that of the outer alloy,and the hardness of the composite layer is higher than that of the inner alloy,while the hardness of the interface is between of them.With the increase of extrusion temperature,the grain size of AZ91/PMMCs clad plate increases,the amount of second phase decreases,yield strength?YS?,tensile strength?UTS?and Vickers hardness decreases,while elongation shows an upward trend.The AZ91/PMMCs clad plate were prepared by extrusion after solution treatment,it is found that Mg₁₇Al₁₂ phases precipitates in the grain interior and grain boundary of clad plate,but most of them precipitates along grain boundary.With the increase of extrusion temperature,the grain size of clad plate gradually increases,the size of precipitated phase increases while volume fraction decreases.As compared with the AZ91/PMMCs clad plate obtained by direct extrusion,the clad plae that pretreated by solid solution possesses higher microhardness,more precipitated phases and finer grain size,and its strength is improved by the dispersion strengthening and refinement strengthening.In addition,the coarse Mg₁₇Al₁₂ phase is dissolved into the magnesium matrix because of the solid solution treatment,which reduces the inconsistency of deformation and improves the elongation The AZ91/PMMCs clad plate obtains good mechanical properties when extruded at 300^oC,the YS,UTS and elongation of clad plate are 272MPa,353MPa and 3.5%,respectively.The AZ91/PMMCs clad plate was rolled at 350^oC,it was found that the rolling formability of PMMCs is significantly improved by introducing AZ91alloy.With the increase of rolling deformation,the homogeneity of the microstructure is improved and the grain size of the clad sheet increases;the volume fraction and size of Mg₁₇Al₁₂ phase decreases,and the microhardness decreases,but the hardness of rolled clad plate is higher than that of pre-rolling clad plate.The tensile strength of rolled clad plate with the reduction of 50%increases significantly,YS and UTS are 341 MPa and 404 MPa,respectively,while EL decreases.During the tensile process,the crack initiation and propagation occur preferentially in the PMMCs layer due to the interfacial debonding between SiC_p and Mg matrix.However,the the existence of the AZ91layer will hinder the propagation of micro-cracks.The rolling deformation of AZ91/PMMCs composite plates with different thickness ratios?1:1,1:2,1:3?can reach 50%.When the thickness ratio of PMMCs increases,the grain size of clad plate increases and the amount of Mg₁₇Al₁₂ phases reduces;the YS,UTS and elastic modulus of clad plate gradually increase,when the thickness ratio is 1:3,the modulus of clad plate is⁵5GPa,but the elongation of clad plate decreases because of the large proportion of PMMCs.