The Study On Microstructure And Properties Of C_sf/AZ91 Magnesium Matrix Composite Fabricated By Stir-casting

Three kinds of short carbon fiber(C_sf) reinforced AZ91 Magnesium alloy: 10%C_sf/AZ91, 15%C_sf/AZ91 and 20%C_sf/AZ91 were fabricated by stir-casting method, then extruded into bars at two kind temperature and three different extrusion ratio. The microstructure of the composites were observed by Optical Microscope(OM), Scanning Electron Microscope(SEM) and Transmission Electron Microscope(TEM); The mechanical properties were tested by tensile test; The Dilatometer(DIL) and the Dynamic Mechanical Analyzer (DMA) were used to investigate the thermal expansion behavior and the damping capacity respectively.There was no macroscopic in the as-cast composites. And carbon fiber distributed homogenous in the AZ91 matrix, though the fiber was broken during the fabrication procedure.The hardness, the yield strength and the elasticity modulus increased with the increasing of the carbon fiber volume fraction, because of the grain refinement. Duo to the increasing of the carbon fiber, the thermal expansion coefficient was reduced gradually. There is no obvious difference among the composites with three different volume fraction, as the energy absorb occurred in the matrix.The grain that refined during hot extrusion became equiaxial and was smaller than before extrusion. The length of carbon fiber was significant reduced after extrusion. The fiber lies parallel to the extrusion direction. After hot extrusion, the mechanical property improved for the increase of density and smaller grain. Because of the directional arrange of fiber, the thermal behavior of composites obtained improved property in parallel direction. Compared with as-cast composites, the damping capacity of composites after hot extrusion was better.