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

Here,the pressure infiltration process of carbon fiber reinforced magnesium matrix composites?C_f/Mg composites?is investigated.Influence of the fabrication parameters such as preform preservation temperature,molten temperature and pressure is also analyzed.By comparing the microstructure and mechanical properties of composites fabricated,parameters for the pressure infiltration process are further optimized.Mimicking the old fish skin structure,we design a multi-layered structure and fabricated laminated composites using pressure infiltration method.The microstructure and mechanical properties of this multilayered composites are analyzed.In this study,three kinds of carbon fibers are incorporated.Study indicated that T300 and T700 carbon fiber can stay at 450? while when the temperature is improved to 500? and upwards DSC results show that carbon fiber is oxidized.However,M40 with high graphite levels is inactive whether at temperature of 450,500 or 550 ?.the performance of carbon fiber to temperature will absolutely affect the performance of composites.As for T700/AZ91 composites,the best bending strength was obtained by using 450 ? and750 ? as its preservation temperature and molten temperature respectively.But it is worth noting that among all the composites,M40/AZ91 composites hold the highest bending strength at about 1300 MPa improved 500% in comparison with that of AZ91 matrix.It is interesting that the presence of SiC particles doesn't improve the mechanical properties of the composites as expected.In contrast,the mechanical properties decline with the addition of SiC particles.This may be attributed to the following reasons: the size of SiC particles is 10 ?m which is too large to perform as a dispersion agent;besides the addition of SiC will scratch the carbon fiber and reduce the properties of carbon fiber.The interface between the carbon fiber and the matrix and the precipitation mechanism of the secondary phase are also analyzed.Interfacial reaction is proved by the observation of Al₄C₃.Besides,beta Mg₁₇Al₁₂ the normal secondary phase present in AZ91 alloy.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 or cracks are found.The Al element segregates on titanium mesh surface and carbon fiber surface.It is worth noting that the Al element prefer to segregate at Ti/Mg interface contributing to the different physical properties between carbon fiber and Ti.