Papers by Author: Yong Bing Liu

Abstract: Cu-based materials reinforced by titanium carbide used in the field of brake or conducting friction were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). X-ray diffraction results indicate that the composites consist of copper matrix, Cu3Ti2, titanium carbide and graphite. Transmission electron microscope (TEM) image shows that a smooth interface exists between the titanium carbide particles and copper matrix. Moreover, the laminate structure of graphite (800°C) transfers to not consistent with the laminate structure at high temperature (1000°C).

Abstract: During Thixomolding process, solid phase fraction decreased with the injection velocity increasing. Meanwhile, the solid phase morphology changed from irregular dendrite to near spherical. Friction heat produced by high speed melt flow could cause partial melt of solid phase, and the morphology of solid phase would form into globular. The dendritic solid phase can be broken by high speed melt flow under the condition of injection velocity higher than 2.0m/s.

Abstract: The microstructure and wear behavior of Cu-TiC composite which prepared by spark plasma sintering (SPS) and mechanical alloying (MA) were discussed in this paper. X-ray diffraction patterns and scanning electronic microscopy (SEM) images indicate that TiC were formed during sintering process. The pin-on-disc wear test was carried. Confocal scanning laser microscope (CFSLM) images indicate that mechanical mixed layer appeared on the worn surface the mechanical mixed layer broken up when normal load reached 200N. The composites displayed excellent wear resistance with 2.38×10−5 mm3/Nm specific wear loss.

Abstract: The Mg-5Li-3Al-1.5Zn-2RE (LaPrCe) alloy was prepared by hot-chamber extrusion process after casting. The alloy consists of α-Mg solid solution and intermetallic phases (Al11RE3 phase and Al2RE phase). The microstructural analysis of the alloy reveals the correlation between microstructure and creep properties. The stress exponent of n varies from 4.25 to 6.23, and the activation energy varies from 104 to 134 kJ/mol. There is a transition between dislocations climb dominated creep mechanism and dislocation creep controlled by non-basal planes slip. Tensile creep tests were combined with detailed transmission electron microscopy in order to characterize the Al11RE3 phase, which had thermal stability at 448K during the creep test. The dislocations pinned and cross-slip dislocations were observed.

Abstract: The oxidation behavior of two ductile cast irons was investigated in this paper. The alloys were a high Si-Mo ductile and a ductile Ni-Resist cast iron which were developed by FAW Foundry. Polished sections were exposed at temperatures between 800 °C and 1000 °C, mostly for 80h. It has been found that the property of oxidation resistance of ductile Ni-Resist cast iron is excellent or better than that of high Si-Mo ductile by comparison and analysis.

Abstract: Magnesium alloy is the lightest metal that can be used as structural material at present. As a novel forming process for magnesium alloys, thixomolding can result in a product with few defects and superior dimensional accuracy, and it is suited to manufacture the thin wall products especially. In this paper, the samples of mobile phone housing were fabricated by 220Tons thixomolding machine made by Japan Steel Works. The effects of barrel temperature, screw rotate rate and injection velocity on the mechanical properties were studied. The relationship between process parameters and mechanical properties was investigated. The results show that the effects of barrel temperature and screw rotate rate on the mechanical properties can be divided to low temperature and high temperature stage. The high tensile strength are corresponding to the best injection velocity.

Abstract: The evenly dispersed Cu-Ti-C composites have been synthesized successfully from the element powders by mechanical alloying (MA) and spark plasma sintering（SPS）techniques. The evolution of microstructure with different processing parameters has been investigated by XRD and SEM. The Cu-TiC and the Cu-Ti2Cu3-C composites with different hardness and density were obtained from different content of Cu, milling time and sintering temperature. The effect of Cu content in the compound powders, milling times and sintering temperatures on the solid solution and reaction process of Cu-Ti-C system was also discussed and analyzed.

Abstract: The stir-casting method was utilized in this paper to synthesize 6063Al/Al2O3·SiO2 reinforced composites consisting of 6063Al alloy as matrix and Al2O3·SiO2 particles as additive with content of 5%, 10%, 15%, 20% (volume fraction) respectively. Al2O3·SiO2 particles were obtained from fly ash particles of Steam Power Plant and were pretreated. The shape of these fly ash particles was spheroidal and ellipsoidal. The damping behavior of 6063Al/Al2O3·SiO2 particle reinforced composites was studied by measuring the composite’s internal friction values on a Multifunctional Damping Measurement Apparatus. Under the condition of this series of experiments, 6063Al/Al2O3·SiO2 particle reinforced composites had a higher internal friction values than that of 6063Al matrix and also showed the dependency of internal friction on Al2O3·SiO2 particles volume fraction, particles dimension, vibration frequency and temperature. There was an increased trend for internal friction values with increasing the volume fraction of Al2O3·SiO2 particles and decreasing particles dimension of Al2O3·SiO2 at the same frequency and the different temperature. It has been found that in the lower frequency, the higher internal friction value was obtained. The internal friction of the composites increased with increasing temperature. In the case of lower frequency, two damping peak were observed. A low-temperature damping peak appeared at a temperature near 245°C which a high-temperature damping peak appeared near 450°C. Based on the experimental results, the damping mechanism of 6063Al/Al2O3·SiO2 particle reinforced composites was preliminary discussed. It may be concluded that the damping mechanisms associated with 6063Al/Al2O3·SiO2 reinforced composites include mainly intrinsic damping, dislocation damping and interface damping. However, only the interface damping mechanism is dominant at high temperature.

Abstract: The evaluating rules for semi-solid microstructure were brought up, and the analysis software was developed on MATLAB 7.0 platform in this study. Furthermore, this system can be used not only in the Thixomolding AZ91D magnesium alloy microstructure analysis, but also in the other semi-solid processing microstructure.

Abstract: Thixomolding® is a new process of net shape parts for magnesium alloys in one step, and it is suited to manufacture the thin wall products, especially to the electronic component shells. In this paper, the sample of mobile phone housing is fabricated by 220Tons Thixomolding® machine made by Japan Steel Works. The effects of barrel temperature, screw rotate rate and mold temperature on microstructure were studied. The relationship between process parameters and microstructure was also discussed in this paper.