Effect of needled structures on in-plane tensile behaviors of 2.5D-Cf/Mg composites fabricated by the liquid-solid extrusion and vacuum pressure infiltration process

Abstract

In this study, a novel magnesium matrix composite (2.5D-C f /Mg) with 2.5-dimensional needled carbon fiber preform and enhanced interlaminar shearing strength was prepared by the liquid-solid extrusion and vacuum pressure infiltration process. The microstructure and interlaminar shear strength (ILSS) of the 2.5D-C f /Mg were fully investigated. Meanwhile, tensile behaviors of the composites were also studied by the tensile tests along 0° / 90° and ± 45° fiber orientations. The results demonstrated that a high-quality infiltration in the composite preform could be realized at the 50 MPa pressure. The micro-cracks were more easily formed in the fiber directional change regions as well as in the vicinal areas of the needled fibers. The ILSS of the composites along ± 45° and 0°/90° shearing directions could reach to 64 MPa and 31 MPa respectively, which was attributed to the stabilizing effect of the needled structures along the thickness direction. The ultimate tensile strength (UTS) of the composites loaded along the 0° / 90° fiber orientation was 203 MPa, 40% higher than the matrix, in which the fracture mode of 0° fibers was interfacial debonding, whereas the 90° fibers were pull-out/rupture. Regarding the 45° loading direction, the peeling/shearing fracture mode was observed for the 45° fibers. The failures of the composites in the above two loading cases were mainly attributed to the damage of needled fibers to long fibers in non-woven cloth ply. • A novel 2.5D-C f /Mg composite was prepared by the liquid-solid extrusion and vacuum pressure infiltration process. • Gradually increasing the pressure, rather than suddenly, can reduce the scouring effect of the liquid alloy on fibers. • The interlaminar shearing strength of the 2.5D-C f /Mg in 45° direction is three times higher than that of the 2D-C f /Mg. • The UTS of the 2.5D-C f /Mg loaded along the 0°/90° orientation can be increased by 40% compared to the matrix. • The long fibers are damaged in needled regions, which reduces the strengthening abilities of the preform to the composite.