On Microstructure And Mechanical Properties Of 2.5D-C_f/Al Composites Fabricated By Vacuum Pressure Infiltration

2.5 dimensional(2.5D) carbon fiber braid is a specical structure in three-dimensional braided. It have many advantages such as simple braided processing, similar property at the warp and welf direction and the structure can be designed. Also, 2.5D braid have excellent inter layer properties and structural integrity. It is an ideal method of weaving the fiber preform. Vacuum pressure infiltration preceded is a processing method that forming at vacuum pressure and solidify at high pressure. It is a method that could fabricate and form material integrated. Moreover, it is a method that could prepare components with precise size and complicated shape. And this could avoid the fibers continuity being damaged on the post processing. Combination both of the advantages above, vacuum pressure infiltration is suit for C_f/Al composites with high property and complicated shape producing.In this paper, matrix alloy was ZL301, reinforcing materials were M40, fiber preform is 2.5D similar plate and 2.5D large flat plate, the volume fraction of C_f is42 %, fiber volume ratio of the warp and welf is 3:2. The structure is 2.5D shallow bend-joint with characteristic of the warp braiding path is the sine curve and the weft is straight line. the study focused on investigating the effect of fiber preheating temperature on the density,microstructure and tensile strength of 2.5D-C_f/Al composites, by the means of x-ray diffract meter(XRD), scanning electron microscopy(SEM), analytical balance(EDS), etc. Based on preparation of 2.5D similar plate, optimization of the process to make the warp and welf 2.5D-C_f/Al composites large plate, then test and analysis tensile and flexural properties at room temperature.The results show that with increasing the fiber preheating temperature, the density increases first and then reduce,the largest of the 2.5D-C_f/Al composites is98.43% at fiber preheating temperature of 570℃.while the fiber distribution in the matrix is uniform. The pore size inside the bunch become smaller,and the pores between the bunch is decreased first and then increase. XRD patterns indicate2.5D-C_f/Al composites is mainly composed of the Al, C, Al4C3 and Al3Mg2 phase diffraction peak.C elements departing from the surface of carbon fiber diffuse into the aluminum matrix, and Al4C3 brittle phase is generated. It is promoted that diffusion ofC elements and Al4C3 with the fiber preheating temperature increasing.The results of the 2.5D similar plate faric composite tensile test indicate that the tensile strength decrease with the fiber preheating temperature increase. 2.5D-C_f/Al composite tensile strength is 274.4MPa with the fracture uneven and a lot of fiber pull-out at the fiber preheating temperature of 530℃.Based on preparation of 2.5D similar plate faric composite, the best process parameters are the preheating temperature, infiltration temperature, impregnation pressure and dwell time of the fiber are set as 530℃, 720℃, 8MPa and 20 min,respecttively. The tensile strengh, poisson ratios and ductility the warp are355.83 MPa,0.19,5.1%.The tensile strengh, poisson ratios and ductility the welf are265.42 MPa,0.24,3.9%. The tensile strengh and ductility warp is larger than the welf,but the poisson ratios is little than the welf. Compared with 3D-C_f/Al composites which has obvious anisotropy, 2.5D-C_f/Al composites exhibited good isotropic properties.Flexural property is like tensile property.The bending strength and flexural modulus of the warp is higher than the warp,but their ratio is smaller than the fiber volume ratio of the warp and weft.The bending strengh and flexural are 384.81 MPa and 123.21 GPa.The bending strengh and flexural are 361.67 MPa and 104.63 GPa.The warp and weft directions of 2.5D-C_f/Al composites the tensile stress-strain carves exhibited mostly nonlinear behavior.The carves can be divided into three stages.Every stage compared with a tangent modulus, and increase first and then decrease, at last increase again.the warp tensile always break in the warp and weft intersection, and the weft break in the weaked point weft.Tensile damage and shear damage are two damage modes for 2.5D-C_f/Al composites flexural fracture in room temperature,the outside surface under tensile is tensile damage, and the inside surface under press is shear damage. Study on the bending fracture, both of fiber bundles exist tilte toward the bending direction, cracking and shear failure, with the fiber uneven.