Papers by Author: Hai Feng Liu

Abstract: Cast Magnesium alloys often exhibit large variability in fracture related properties such as ductility. In this study, the characteristics of micro-voids in high-pressure die-cast (HPDC) AM50 alloy were investigated by microstructural detecting. Specimen-to-specimen fractographic analysis of tensile fractured surface was executed to summarize the relation between microporosity and tensile properties. The results indicated that the variability in tensile properties is quantitatively correlated to the areal fraction of porosity in the corresponding fracture surface, which could be expressed by a power law equation. All the results proved that the most highly localized cluster of micro-voids is most preferentially to be the origin of fracture, and then, fracture crack will preferentially propagate through the adjacent regions that with large porosity.

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: Casting properties and process improvement of A356 aluminium alloy which is used to cast automobile engine cylinder is investigated in the present paper. The effects of flow field and temperature field on the microstructure and defects distribution of A356 is analyzed by ProCAST software. Simutaneously, the mold filling and solidification of the bottom gating and rotated solidification technology is simulated. Thus, the optimize process parameters obtained by calculating is pouring temperature 725°C, pouring times 21s, and preheating temperature of cylinder sleeve 450°C. Then, the cylinder is made under the condition of above parameters and the microstructure of the cylinder was observed. The results show that the microstructure and defects distribution which is simulated by ProCAST software are good agree with the experiments. Keywords：ProCAST; Aluminium alloy cylinder; Flow field; Temperature field;

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: A series of high temperature creep resistant magnesium alloys for die casting based on AZ91 were successfully developed by the addition of Rare Earth, and Calcium. The original target of magnesium alloy development was aimed at cylinder head cover of high power diesel engine, and tried to satisfy the temperature demands of gear-box house. The tensile property at room temperature, creep behavior at 150ı，and analysis of microstructure were discussed in this paper. The results showed that these alloys has potential for die casting to produce power-train parts, and greatly decrease the weigh of parts.