Papers by Author: Yan Xiang Li

Abstract: Large size Gasar ingots have the advantage of cost saving and productivity improvement, while little attention has been paid to the preparation of large size ingots, especially those with high structural quality. Bridgman method was introduced to fabricate large size Gasar metal ingot. High quality Gasar Cu cylinder sample of 150 mm in diameter and about 200 mm in height (weighing about 20 kg) was obtained at a proper withdrawing velocity. Pore structure distribution at different heights and radii in the sample was measured and analyzed in detail using the image analyzing software. The results showed that the pore aspect ratio changed slightly along the sample height. All the other structure parameters including porosity, penetrative porosity, penetrative pore area and number ratio, pore diameter, pore length and the pore aspect ratio kept almost constant at heights of over 65 mm, while they all varied little along the sample radius. Most of the pores were straight and round. The results suggested that Bridgman method was feasible for the fabrication of large size high quality Gasar metal ingots. This would promote the commercial application of Gasar metals, such as Gasar Cu for micro-channel heat sinks.

Abstract: Aluminum foams from A356 base alloy were produced by both the melt foaming process and gas injection foaming process. A comparison of microstructures between the two kinds of aluminum foams was carried out. The related causes were analyzed to form the difference in microstructure. Results indicate that aluminum foams produced by different processes are distinct in metallurgical structure. The average thickness of cell wall, the species and area fraction of secondary phases or particles and other metallurgical features have been all comparatively studied. The difference in microstructure features of the cell walls will also make the aluminum foams different in mechanical properties. Therefore, we need to select proper foaming process for aluminum foams according to the property requirements in practical application.

Abstract: A kind of austempered boron alloyed high silicon cast alloy was developed though modification with Ti and controlling austempering temperature, the impact toughness of which increases to 20.7 J/cm², which is more than triple that of the previous work. The alloy with modification exhibits obvious grain refining both in matrix and boride, improved the morphology of boride into discontinuous network and small particles. The phenomenon and mechanism are discussed in the article, it proved TiC is possible to act as the nuclei of eutectic boride and Ti can be an effective modifier.

Abstract: Metallic foams of A356 alloy with a uniform porosity of 75-85% were produced with the melt foaming process. The microstructure inside the foam cell walls was experimentally studied. It is found that the microstructure is greatly different from the as-cast structure of the base alloy. It is believed that the thickening process with calcium, the adding of foaming agent and the mixing process during the production process all play important roles on the solidification microstructure of the cell walls. The morphology and grain size of primary α-phase, the amount and morphology of eutectic silicon, the distribution and size of CaSi2Al2 and residual titanium hydride particles were studied. The sound absorption coefficient of the alloy foams was measured. Two methods, drilling small holes and compressing the foam, have been developed to improve the sound absorbability of the alloy foam in low and middle frequency ranges.

Abstract: In order to clarify the effect of antimony on graphite morphology and mechanical properties in heavy section ductile iron, experiments were carried out using a newly developed thermal simulation system. Results show that with 0.011% addition of antimony, tensile strength of heavy section ductile iron are obviously improved by elimination of graphite degeneration in it, and the effect of antimony is increased when the addition is increased to 0.02%. In the range of 0.01~0.04%, antimony is beneficial to graphite morphology and tensile strength although the advantageous effect on them become not so obvious when addition is exceed 0.02%.

Abstract: The influence of rare earths(RE) and Mg compound modification on eutectic carbide morphology and matrix of high speed steel(HSS) roll was investigated. The results show that the matrix can be refined by the RE-Mg compound modifier, the eutectic carbides are inclined to turn into small lump, whose distribution is homogeneous. After modification, the heat conductivity coefficient of HSS is increased and heat expansion coefficient is decreased. Moreover, RE-Mg modification is able to increase the cycles of thermal fatigue crack initiation and decrease the propagation rate. After cycling 700 times at the condition of heating at 600oC and cooling in 25oC water, the length of thermal fatigue crack is lessened by 41.12%.