Papers by Author: Zi Tian Fan

Abstract: In order to improve the mechanical properties of A356 aluminum alloy in lost form casting (LFC), vibration and pressure were applied to solidification process of LFC, and the microstructures and the mechanical properties of the castings were compared with that of the castings in LFC without vibration and pressure. The results indicated that the grains of A356 alloy with vibration pressure in LFC became finer, and the dendrites decreased, and the equiaxed grains increased. At the same time, the porosities of the castings were significantly reduced. Compared with conventional LFC, the tensile strength, elongation, and hardness of A356 alloy with vibration pressure in LFC were all increased by 10% or above.

Abstract: In this study, three dimensional structures are fabricated by a self-developed three dimensional printing machine with eight different particle size distribution scrubbed silica sand. In order to evaluate particle size distribution effect on the properties of sand mold, the physical and mechanism properties of printed specimens, including weight, gas evolution, air permeability, tensile strength and compressive strength, were measured. The mechanism of effect was analyzed and studied. The results show that the printed specimens from the 80-140 mesh sand powder have the best comprehensive properties. Both wider and narrower particle size distribution adversely affects the properties of printed specimens.

Abstract: The effects of Cu addition on microstructure, mechanical properties and damping capacity of Mg-3%Ni based alloy were investigated by using tensile tests, X-ray diffraction, scanning electron microscope and dynamic mechanical analyzer. The results show that Cu addition could reduce the size of -Mg dendrites and a new binary phase Mg2Cu can be identified, which mostly distributes among the inter-dendrites in the form of typical lamellar-like eutectic microstructure and improve the mechanical properties. In low strain amplitude, with the increase of Cu addition, the damping capacities of Cu contained alloys change little, while in high strain range, the internal friction values decrease gradually with the grain refinement and increasing content of eutectic phase.

Abstract: The vibration is superimposed to the filling process of aluminum and magnesium alloy in lost foam casting, and the flow lengths and the molten metal temperatures of the flow front are collected, and they compared with no-vibration. The results show that the vibration can significantly improve the filling capacity of the aluminum alloy, magnesium alloy in lost foam casting. Compared to the samples without vibration, the flow lengths of A356 alloy with vibration in lost foam casting increased by 33% and that of AZ91D alloy increased by 15%.The heat transfer of molten metal on the flow front was analyzed, and it indicates that the vibration energy extends the filling time of the molten metal on the flow front in lost foam casting.

Abstract: Fluidity of ZL101 aluminium alloys in the low-pressure lost foam casting (LP-LFC) process has been investigated by altering various temperature variables. The experimental results indicate that the LP-LFC process had fine fluidity, and the pouring temperature was lower than conventional lost foam casting. The effect of the metal temperature on the fluidity is marginal in the LP-LFC process. Excessive pouring temperature not only aggrandizes energy consumption but also deteriorates porosity defect. The success of casting cooling fin demonstrates the advantages of LP-EPC process in producing high-complicated castings.

Abstract: The microstructures and mechanical properties of Mg9AlZnGdY alloy after T6 heat treatment in lost foam casting (LFC) are compared with that of AZ91D magnesium alloy. The results show that the microstructures of Mg9AlZnGdY alloy after T6 heat treatment consist of the α-Mg solid solution, β-Mg₁₇Al₁₂ precipitation phase, a small amount of rod Al₂Y and block Al₂Gd phases, which are distributed over grain boundaries of the α-Mg phase. The thermal stability of Al₂Y and Al₂Gd phases offers the pinning effect on the grain boundary under high temperature, and therefore, the grain boundary sliding is eliminated and the high-temperature strength is increased. After the T6 heat treatment, the tensile strength of Mg9AlZnGdY alloy was 235MPa at room temperature, and 156MPa at 200°C. Compared with that of AZ91D alloy, the tensile strength was increased by 19.3% and 38.1% respectively.

Abstract: Mechanical vibration was introduced into the solidification in order to overcome the defects of coarse microstructure and low mechanical properties of the AZ91D magnesium alloy via lost foam casting（LFC）. The microstructure with fine uniform dendrite grains were achieved with mechanical vibration, which was mainly attributed to the cavitation and the melts flow induced by the mechanical vibration. The mechanical vibration has strong influence on the mechanical properties of AZ91D alloy. With application of mechanical vibration, the ultimate tensile strength and elongation of the AZ91D alloy increase 23% and 26%, resepectively.

Abstract: A new technique of introducing gas bubbles during isothermal period of AZ31 magnesium to prepare semi-solid slurry has been reported. The effect of resting time after stirring on the microstructure of the slurry is discussed. Results show that the dendrites and liquid phase reduced, the non-dendritic grains grew up and became spheroidized. A fully grain-refined structure can be obtained with 60s resting time.