Papers by Author: Li Zheng Su

Abstract: 10vol. % Csf/AZ91D composites were fabricated by extrusion following vacuum infiltration process with self-developed experimental device and measuring system. The relationships of load vs displacement during process and surface quality of composites at various extrusion temperatures were investigated. SEM microscope was used to observe the microstructure of fabricated composites. The experimental results showed that the extrusion process can be divided into three deformation stages. The extrusion temperature had a great influence on the maximum extrusion load. Based on proper infiltration parameters, a extruded bar with good surface quality was obtained at extrusion temperature of 420°C.

Abstract: Extrusion directly following vacuum infiltration is a special forming technique that combines the advantages of liquid metal infiltration and semisolid extrusion. The major advantages of this process are elimination of porosity and shrinkage, good surface finish, good dimensional accuracy, high strength to weight ratio and near net shaping. Magnesium matrix composites are fabricated usually through stirring casting, powder forming, injecting deposition, liquid metal infiltration or die casting at present time. However few investigations on magnesium matrix composite are conducted for the specific characteristics of magnesium alloy, such as high chemical activity and easy oxidation. The present paper is focused on Csf/Mg composites obtained via infiltration of porous short carbon fiber preform by liquid Magnesium. The complete experiment setup is designed and fabricated by ourselves, which include the forming molds, the unit for melting the magnesium, the unit for vacuuming and the monitoring and collecting system of forming process parameters. In this method the whole experiment setup is vacuumed firstly. Then the pressurized nitrogen is used to infiltrate the magnesium melt through a porous preform of short carbon fibers. After the infiltration completed, the punch of the press extrude the magnesium-infiltrated preform out of the forming die to form the tubes or bars. X-ray diffraction (XRD), optical and SEM microscopes were used to characterize the infiltration and the microstructure of fabricated composites. The compression test was used to characterize the mechanical properties of fabricated composites. The results show that the preform was infiltrated thoroughly by melt magnesium and the fabricated Csf/Mg composites have excellent mechanical properties compared with the magnesium alloys. Csf/Mg composites should be very promising candidates for automobile parts and portable electronic appliance parts in the future.

Abstract: The pressure infiltration process of porous preforms by molten metals was investigated numerically in this paper. The finite element model of heat and mass transfer of the infiltration in liquid infiltration extrusion process was founded by the introduction of a new continuum model of fluid in porous medium and a distribution resistance concept. The proposed model can describe the transient flow behavior of semisolid materials qualitatively. Numerical simulations were developed in particular for non-isothermal infiltrations which take into account the thermal aspects (the mould, the fibres and the metal are initially preheated at different temperatures). The temperature distribution, infiltration front and infiltration depth in the infiltration area were gained by the simulation of ANSYS／FLOTRAN code. It is shown that the fiber volume fraction and initial temperature have a strong effect on the infiltration process. The simulation results of axisymmetric infiltration have a good agreement with their experimental ones. In addition, the infiltration time was predicted to get the effective infiltration depth based on the simulation results.