Papers by Author: Li Ping Wang

Abstract: Ductile iron was prepared through Sandwich Process and annealing treatment was carried out. The effects of annealing treatment on the microstructure, mechanical and damping properties of ductile iron were studied by means of metallographic microscope, scanning electron microscope, transmission electron microscope, universal test machine and dynamic thermal mechanical analyzer. The results show that annealing treatment has little effect on the morphology and distribution of graphite cast iron, but it will lead to the decrease of pearlite content in the matrix, the increase of ferrite content and the disappearance of cementite. Annealing transforms the fracture form of ductile iron from cleavage fracture to quasi-cleavage fracture, which greatly increases the ductile fracture area of the matrix compared with the as-cast, and tends to develop ductile fracture. The annealing treatment results in a decrease in the tensile strength of the ductile iron, but it can increase the plasticity and increase the elongation after fracture to 7.5 times that of the as-cast state. The damping value of as-cast ductile iron increases first and then decreases with the increase of temperature, and peaks at 190 °C when Q^-1 is 0.025. The damping value of annealing ductile iron decreases with increasing temperature. The damping value increases with increasing strain amplitude before and after annealing. Annealing treatment will reduce the sensitivity of the damping property of ductile iron to strain amplitude.

Abstract: The Mg-6Al-xCa-xNd alloys, which were alloyed by Ca and Nd element on basis of Mg-6Al alloy, were fabricated by gravity permanent mould method. The microstructure and mechanical property were characterized by scanning electron microscope (SEM) and X-ray diffractometer (XRD). Experimental results show that the microstructure of as-cast Mg-6Al alloy is with typical dendritic morphology, which is consist of α-Mg matrix and divorced eutectic β-Mg₁₇Al₁₂ phase along the grain boundaries. With increasing of Ca and Nd elements content, the α-Mg grains of Mg-6Al-Ca-Nd alloy were refined obviously, and the dendritic structure disappeared and equiaxed grains appeared. Meanwhile, β-Mg₁₇Al₁₂ phase decreased until disappeared and intermetallic Al-Ca phases and Al-Nd phases increased.

Abstract: In this paper, WC particles and NH4HCO3 powders were mixed evenly, and then pressed under 150MPa. The WC porous preforms were obtained after the compacts being heat treated to eliminate NH4HCO3. The volume ratios of WC in the preforms were 30%, 40% and 50% respectively. WC/Fe composites were fabricated by infiltrating liquid cast iron into the WC porous preforms. Optic microscope and scanning electron microscope were employed to observe the microstructure of the matrix alloy and the composites. The results showed that matrix alloy without WC addition had pores in the surface. The microstructure of the composites with WC volume fractions of 30%, and 40% were denser than that of 50%. Hardness and wet sliding wear behaviors of the composites were investigated at room temperature. The addition of WC particles could effectively improve the hardness and the wear resistance of the composites. The influence of volume fractions on hardness of the composites was similar to that on wear resistance. The hardness and the wear resistance of the 40vol.%WC/Fe composite was better than those of the 30vol.%WC/Fe composite. And the properties of the 50vol.%WC/Fe composite were the worst.

Abstract: A commercial software, MAGMASOFT, was used to simulate the ZM5 shell with different materials of chills. The calculated results of solidification are obtained. Shrinkage porosity is predicted by means of a built-in porosity criterion. It shows that using the different materials of chills, such as copper, gray iron and steel, a large amount of shrinkage porosity defects are formed in ZM5 shell. However, with graphite as the material of chills, shrinkage porosity defects of ZM5 shell can be effectively reduced.

Abstract: Application of spheroidal graphite cast iron in the production of spent-nuclear-fuel container contributes to improve the strength and toughness of the casting, because of the nodular shape of graphite. For a large-scale container, a forced-chilling technique is used to accelerate solidification process and raise spheroidization rate. In this paper, modeling of heat transfer in the container is performed. Influences of cooling media, inflow flux of coolant and thickness of sand layer upon the variations of cooling rate are systematically analyzed. Calculated results indicate that water as a coolant is more capable of enhancing the cooling course than air. Increasing inflow flux conducts an effective cooling job, whose influence is more apparent for air-cooling than for water-cooling. The role of decreasing the thickness of sand layer is most pronounced for raising solidification rate. The predicted cooling curves are compared with experimental measurements to validate the model.