Study On Fabrication, Microstructure And Properties Of C_f/Mg Composites

In the present work, pressure infiltration process of carbon fiber reinforced magnesium matrix composites(C_f/Mg composites) is studied. Influence of the preform preservation temperature, melt temperature and preform structure on the microstructure and mechanical properties is investigated and optimal parameters for the pressure infiltration process are obtained. Then magnesium matrix composites reinforced with unidirectional carbon fiber and 2D-carbon fiber are successfully fabricated based on the optimized parameters. Effects of the matrix composition and fiber orientation on microstructure and mechanical performance in the synthesized composites are studied.Studies have shown that the best way to clean carbon fiber is the combination of first step ultrasonic cleaning in the mixture of acetone and ethanol for 1h and the second step heating at 450℃for 20 min. Better mechanical properties of the composites can be obtained by the following optimal parameters: preform prepared by winding carbon fiber by 5 ° around graphite rod or packing the carbon fiber pieces into the graphite groove, 450℃ as the preservation temperature and 800℃ as the melt temperature. Among the fabricated composites, the ones reinforced by the unidirectional carbon fiber have the highest flexural strength and modulus, which reach to 870 MPa and 164 MPa(350% higher than matrix alloy), respectively.Interface condition between the carbon fiber and the matrix and the precipitation mechanism of the secondary phase are also investigated. Interface reaction is observed and the secondary phases mainly include beta Mg17Al12, needle-like phase Al4C3 and lamellar phase Mg2 Si. The valid strengthening mechanism are thermal mismatch strengthening, load transfer and Orowan strengthening by the nanoscale second phase formed at the interface.Uniform microstructure is realized in the bionic structure of Ti/Mg/C_f composites fabricated by the optimal process and no porosities and cracks are found. The Al elements segregate on titanium mesh surface and the second phase in the Ti/AZ91/C_f form a continuous mesh pattern around the titanium mesh material leading to the more profound brittleness. As for 2D carbon fiber reinforced magnesium composites, after joining titanium net, not only the strength of the material is improved but also the deflection of the material. The strength of composites is improved by 40 MPa. The good mechanical properties mentioned above indicate that the joining of titanium mesh can be beneficial for ductility enhancement and thus meet the demands for material design.