Papers by Author: Guang Hui Min

Abstract: The microstructure of magnesium alloy sheets (nominal composition Mg–6Zn–Y in at. %) was investigated with the Optical Microscope (OM), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) technique after the annealing treatment. Tensile test at room temperature was performed to show the influence of annealing treatment on mechanical properties. Experimental results indicate that there are a large number of twin crystals appearing in microstructure of the extruded Mg-Zn-Y alloy sheet at 350 °C. The distinct icosahedral phase appears on the α-Mg matrix in granular form and the strength gets largely improved to the maximum. The uniform distribution of isometric crystal contributes to the best elongation at the annealing temperature of 400 °C.

Abstract: Lathanum hexaboride films were deposited by dc magnetron sputtering with the same sputtering parameters. AFM, XRD, Raman spectrum was used to characterize the film. The as-deposited films were annealed at 400 ^oC, 500 ^oC and 600 ^oC, respectively. After 400 oC’s annealing, morphology of fracture cross-sections of the films exhibited evolutions from columnar to the equiaxial, and the crystallinity of the film was improved as well. It was also found annealing process generated negative effect on the film’s hardness and elastic modulus.

Abstract: A series of Si (100) based LaB₆ films were deposited by D.C. magnetron sputtering with different argon pressure, one of the most important deposition parameters, which affect both the structure and properties of the thin films. XRD, AFM, Raman, and Hall measuring instrument were used to characterize the film structure and performances. It was found that argon pressure strongly influenced the condensing particles’ kinetic energy obviously through affecting the scattering processes of sputtered energetic particles, which played a crucial role in the growth of the LaB₆ films. LaB₆ film deposited at 1.0 Pa showed a higher crystallinity degree. Morever, the film displayed a more uniform structure and better electrical property, the relationship between microsture, electrical property and crystallinity were demonstrted as well.

Abstract: Horizontal continuous casting (HCC) Al-18%Si alloy billets were prepared with the addition of fine-grained Al-18%Si as a master alloy. The influence of cooling conditions and this fine-grained structural materials addition on the microstructure and tensile properties were studied. The uniformity of the HCC Al-18%Si alloy billets was also analyzed. The results denote that the HCC Al-18% Si alloy billets showed finer microstructure and better mechanical properties after double cooling. Fine-grained structural material addition can effectively reduce macrosegregation and make both primary and eutectic silicon much finer. The ultimate tensile strength clearly increased with an addition of 15 percent fine-grained structural material compared to the HCC alloy with no addition of fine-grained structural material. However, a small decrease occurred after an addition of fine-grained structural material up to 30 percent.

Abstract: Lanthanum hexaboride (LaB₆) films were deposited on Si (111) substrates by magnetron sputtering method. The characterization of the films was investigated by means of atom force microscopy (AFM), X-ray diffraction (XRD), four-point probe electrical resistance measurement, scratch tester and nano-indentation tester. Influence of argon pressure on physical properties, such as crystallization degree, conductivity and mechanical properties was studied. All the films were smooth and dense. The film crystallites showed a preferential orientation of (100) plane, but the films which were deposited at 2.0 Pa exhibited amorphous structures. LaB₆ films which were deposited below 1.5 Pa had excellent conductivity. The bonding strength of the films which were deposited at 1.0 Pa was higher than the others due to the formation of the nano-sized crystals. The hardness and elastic modulus were investigated in connection with the crystalline of LaB₆ films. As a result, the films which were deposited at 1.0 Pa had a maximal value of hardness (16.782 Gpa) and elasticity modulus (193.895 Gpa). In a word, the LaB₆ films which were deposited at 1.0 Pa have a higher degree of crystalline and more excellent physical properties in comparison with the others. The obtained results will be used synthesizing LaB₆ films for applications in low-temperature thermoelectric devices.

Abstract: Crystal structures and shape memory properties of Ti-rich Ti52Ni23Cu25 (at.%) ribbon annealed at 450°C for 10 min and 1 h were investigated by X-ray diffraction and dynamic mechanical analyzer. As-spun ribbon was full amorphous and its crystalline peak temperature is 455.4°C. The annealed ribbon is crystallized with strong preferential (110)-B2 orientation. It shows a well-defined shape memory effect and the transformation hysteresis for the annealed ribbon under an external load in the range of 3-9 N is about 38.5°C. With annealing time increasing from 10 min to 1 h, the maximum of transformation strain under the external stress decreases from 1.93% to 1.7%. The temperature dependence of the external stress increases from 0.3 N/°C to 0.43 N/°C. The residual plastic strain is up to about 0.4% at a load of 9 N.

Abstract: The microstructure of a twin roll cast (designated as TRC in short) and warm rolled Mg-4.5Al-1.0Zn (designated as AZ41 in short) alloy was investigated using OM and TEM after annealing treatment at the temperature range of 300oC~400oC. Tensile test was performed to show the influence of the annealing treatment on mechanical properties. The microstructure of AZ41 alloy sheet consisted of fibrous structure of elongated grains and shear bands along the rolling direction. Static recrystallization (SRX) was observed at and above 300oC during annealing treatment process. Shear bands, dislocations and twins play an important role during SRX and serve as nucleation sites, this leads to grain refinement. The sheet had higher strength and lower elongation after warm rolling. However annealing treatment after warm rolling induced the decrease of strength and increase of elongation. This results in the balance of strength and elongation in AZ41 alloy sheet. Annealing treatment at 400oC for 40min can be considered to be the optimum annealing treatment, and at this condition the tensile strength, yield strength and elongation are 375MPa, 285MPa and 17.7%, respectively.

Abstract: SiCp reinforced copper matrix composites with the reinforcement content of 30-50vol. % were fabricated by hot pressing using Cu-coated and uncoated SiC powder. And the microstructure and electrical conductivity of the composites were also studied. The results showed that with the increasing of SiCp particle size, the electrical conductivity of the composites also increased. And the oxides in the composites can decrease the electrical conductivity of the composites obviously. The electrical conducting property of the composites can be improved by the copper coating layer and suitable annealing treatment. It provided important data for the application of SiCp/Cu composites as electronic packaging materials.

Abstract: In this study, an ultrastrength Al-10Zn-3.2Mg-2.3Cu alloy was fabricated by powder hot extrusion technique. The microstructures of powder, extruded and subsequently heat treated rods were investigated by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) for compositional analysis. During extrusion, more MgZn2 compounds were precipitated from the supersaturated Al matrix and observed on the grain boundaries and in the grain interiors. The microstructure of as-extruded alloy is composed of Al matrix and MgZn2 phases in different shapes. After solution treating, the MgZn2 phases were mostly dissolved into matrix and the major constituent are Al7Cu2Fe phase as well as oxides. The mean size of grains was controlled to 2.5μm, and the major precipitates were GP zones and/or η’(MgZn2) phases in the Al matrix after peak-aging (T6) treatment (120°C for 20h). The ultimate tensile strength (σb), yield strength (σ0.2) and elongation (δ) are 745Mpa, 690MPa and 9.0%, respectively.

Abstract: The Al-Mg-B polycrystalline bodies were prepared using vacuum hot-pressing sinter method by pure Al, Mg and B powders. Process parameters and constitution variation were investigated to obtain compact Al-Mg-B sintered body with high mechanical properties. Al-13%Mg-72.7%B(weight ratio) sintered body prepared under 1600°C, 30MPa for 1 hour in vacuum was proved to be optimum, which bending strength was 156MPa and Vickers hardness was 2220. X-ray diffraction (XRD), Micron Probe Micro-analyzer (EPMA) were employed to analyse the ultimate phases. The results showed that the matrix phases were metal borides including AlB12, MgB6 and AlMgB14, while Al2O3 and MgAl2O4 phases existed which connected or filled in the matrix grains to promote the compactness degree, where oxygen introduced from impurities in raw materials. A portion of Mg in AlMgB14 combined with oxygen during heating to 1600°C which helped to form MgAl2O4 and AlB12 in the end.