Papers by Author: Si Cong Zhao

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: 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.