A Study Of The Microstructure And Mechanical Property Of Carbon Fiber Reinforced Magnesium-Gadolinium-Zinc Compoites

In this study, long-period-stacking-ordered(LPSO) phases were introduced to carbon fiber reinforced magnesium-gadolinium-zinc(Cf/Mg-Gd-Zn) composites by adding Gd and Zn with the atomic rate of 2:1 into the matrix, and a new and practicable method of design and optimize the interfacial structure was found. The Cf/Mg-Gd-Zn composite was fabricated by pressure infiltration method. The morphology, distribution, and crystal structure of precipitates were observed and analyzed by transmission electron microscope(TEM), and the chemical compositions of which were detected by energy dispersive spectroscopy(EDS). The mechanical properties of Cf/Mg-Gd-Zn composite were tested on a universal testing machine(INSTRON-5569). Moreover, the effect of microstructure on mechanical properties was discussed.LPSO phases were precipitated both at the interface and in the matrix during the heat treatment of Cf/Mg-Gd-Zn composite. The LPSO phase at the interface was long rod-like, with the length of about 500-1000 nm, who seemed to nucleate on the surface of carbon fibers and grew preferentialy about perpendicular to the axis of carbon fibers. The LPSO phase in the matrix was long and short rod-like, sharing the length of around 100-1000 nm. The long rod-like LPSO phase arranged in a certain angle with the axis of the adjacent carbon fiber, while the short rod-like LPSO phase dispersed uniformly in the matrix. The chemical composition of LPSO phases at the interface and in the matrix are Mg79.06Gd19.88Zn1.06(at.%) and Mg84.96Zn15.03(at.%), respectively. The carbon fiber with high volume fraction contributed a lot to the difference between LPSO phases at the interface and which in the matrix.Moreover, carbon fibers dispersed uniformly in Cf/Mg-Gd-Zn composite, without defects, i.e. inclusions and holes. Gd atoms tended to segrege on t he surface of fibers, and formed the Mg-Gd interfacial layer, the thickness of which is about 100-300 nm. However, Zn atoms prefered to disperse uniformly in the matrix. Beside, Mg-Gd and Mg-Zn intermetallic, such as Mg3 Gd 和 Mg5 Gd were also observed in the composite except LPSO phases. Also, dislocations tangling with precipitates were found at the interface.The mechanical properties of Cf/Mg-Gd-Zn composite were improved by LPSO phases. It was clearly that the bending strength and interlaminar shear strengt h were enhanced to 61.2±3.3MPa and 1479.0±117.5MPa,respectively, and were improved by about 26.4% and 25.7%, respetcively, compared with Cf/Mg composite. The bulky Mg-Gd intermetallic were inhibited, and the interfacial structure was due to LPSO phases. Thus, the load could transmite through the interface effectively. What’s more, the LPSO phase in the matrix can be regarded as short fibers, which can also contribute to the improvement of mechanical property.