Papers by Author: Hua Shun Yu

Abstract: The microstructure and macrotexture of ZK60 alloy sheet were investigated through OM and XRD, which were produced by twin roll casting and sequential warm rolling. Microstructure of twin roll cast ZK60 alloy changed from dendrite structure to fibrous structure with elongated grains and high density shear bands along the rolling direction after warm rolling process at different rolling parameters. The density of shear bands increased with the decreasing of the rolling temperature, or the increasing of per pass rolling reduction. Dynamic recrystallization could be found during the warm rolling process at and above 350oC, and many fine grains could be found in the shear band area. The warm rolled ZK60 alloy sheet exhibited strong (0001) basal pole texture. The formation of the shear bands tends to cause the basal pole tilt slightly to the transverse direction after warm rolling. The intensity of (0001) pole figure increased with the decreasing of rolling temperature, or the increasing of per pass rolling reduction.

Abstract: In this study, SiC particles reinforced aluminum matrix composite was successfully fabricated using powder metallurgy technique followed by hot extrusion. The phases were identified by XRD and the microstructures were observed by SEM. The results showed that only Al and SiC phases existed in the composite, SiC particulates were well distributed in the aluminum matrix and the interface between Al and SiC was clean and well combined. Meanwhile, thermal conductivity and coefficient of thermal expansion of the composite were investigated, the research showed that thermal conductivity decreased as SiC_p content increased because of poor thermal conductivity of SiC_p and increased crystal defects forming during the fabrication process. And the same to thermal conductivity, coefficient of thermal expansion of the composite decreased as SiC_p content increased because SiC_p can acted as obstacles to the motion of dislocations, which can hinder the hot movement of electronics.

Abstract: The effects of titanium modification, which was added along with the pouring liquid in ladles, on the hardness and its distribution of cast steel ZG45 smelted in intermediate frequency induction furnace were studied. Titanium modification increased the hardness of cast steel effectively. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, causing the serious crystallographic lattice distortion. So the hardness increased. Proper content of titanium prompted more even hardness distribution across the whole temperature front section. However, overdoes titanium modification easily caused mass nitrides or oxides, which kept solid phases with high meting point in metal liquid to cause difficulties in metal liquid filling and shrinkage, resulting in less concentrated shrinkage cavity and serious structure rarefaction. The hardness ratio between that of internal and external with overdose titanium modification decreased instead compared to that of none modification.

Abstract: Equal channel angular pressing (ECAP) has been conducted on as-extruded Mg-Zn-Y alloy containing quasicrystal phase at a temperature of 523 K. The optical images indicate that after 8 ECAP passes through route BA, the grain size of the extruded alloy is decreased sharply; and the coarse eutectic icosahedral quasicrystal phases (I- phases) are broken and dispersed in the alloy; and the distributions of Zn and Y elements become more homogeneous. These can be attributed to the shear effect during the ECAP processing. TEM micrographs show the grain refinement, the evolution of broken and dispersed I- phases and dispersion precipitation of nano I-phases during 1- ,4- and 8- pass ECAPed Mg-Zn-Y alloy. And the mechanism of grain refinement is also discussed.

Abstract: The effects of titanium modification, which was added along with the pouring liquid in ladles, on the shrinkage porosity and cavity of cast steel ZG45 smelted in intermediate frequency induction furnace were studied. The metal liquid fluidity was measured by casting spiral samples. 0.2 wt.% titanium modification achieved the highest fluidity for steel liquid. Proper content of titanium could effectively increase the volume of concentrated shrinkage cavity, and restrain the forming of shrinkage porosity. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, diminish the strong dendrite, and increase the fluidity and feeding capacity of steel liquid. However, overdoes titanium modification easily caused mass oxide TiO2, which kept solid phases with high meting point in metal liquid to increase its viscosity and decrease the fluidity. Meanwhile, these solid state titanium compounds enlarged the composition supercooling, so the metal liquid changed from sequential solidification to simultaneous solidification, resulting in inadequate metal liquid feeding, less oncentrated shrinkage cavity and serious shrinkage porosity.

Abstract: In this study, AZ91 and SiC particulates reinforced AZ91 (SiCp/AZ91) magnesium alloys were successfully fabricated using rapid solidification/powder metallurgy technique followed by hot extrusion. Microstructural evolution and mechanical properties of the monolithic AZ91 and SiCp/AZ91 magnesium alloys were evaluated. SiC particulates were well distributed with only few agglomerated particles. The porosity level and microhardness increased as SiCp content increased because the increased surface area of SiCp, harder ceramic phases and SiCp acted obstacles to the motion of dislocations. In addition, an increase in particulate reinforcement content was observed to decrease mechanical properties of the composite compared with the unreinforced counterpart due to increasing agglomerating regions and porosity, brittle interface debonding between matrix and SiCp.

Abstract: The effects of titanium modification, which was added along with the pouring liquid in ladles, on the shrinkage porosity and cavity of cast steel ZG35 smelted in intermediate frequency induction furnace were studied. Proper content of titanium could effectively increase the volume of concentrated shrinkage cavity, and restrain the forming of shrinkage porosity. The concentrated shrinkage cavity was analyzed quantitatively by stuffing wet gluten and draining water method. The maximal cavity arrived at 0.15wt.% titanium modification. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, diminish the strong dendrites, and increase the fluidity and feeding capacity of steel liquid. However, overdoes titanium modification easily caused mass nitrides or oxides, which kept solid phases with high meting point in metal liquid to increase its viscosity and decrease the fluidity. On the other hand, these solid state titanium compounds enlarged the composition supercooling, so the metal liquid changed from sequential solidification to simultaneous solidification, resulting in inadequate metal liquid feeding, less oncentrated shrinkage cavity and serious shrinkage porosity.