Jian Fei Sun

Influence of DC-Joule Heat on Giant Magneto-Impedance of Co-Based Melt Extraction Wires

Co68.25Fe4.5Si12.25B15 naked amorphous wires of 60μm in diameter are prepared by melt extraction technology and annealed by DC-Joule heat at current from 40mA to 250mA for 10min. Impedance response is measured at low frequencies(≤13MHz) using HP4192 impedance analyzer. We get better GMI effect by heating wires at 60mA and 180mA.The connection between GMI response and transformation of structure under different heat current has been discussed. After proper heat treatment, magneto impedance response is strong even at 0.5MHz with GMI amplitude of 193.1% and field sensitivity of 59.4%/Oe. The maximum △Z/Z reaches 476.9% and the largest field sensitivity is up to 91.8%/Oe. These results indicate proper annealed Co-based melt extraction wires are suitable for high sensitivity sensor applications.

Hot Deformation Behavior and Processing Map of a Nickel-Base Superalloy GH4169

The hot deformation behaviors of the nickel-base superalloy GH4169 have been studied by isothermal constant true strain rate compression testing at 950°C-1150°C, 0.01s-1-10s-1 and the height reduction 50%. The processing maps of GH4169 alloy have been constructed at different strains on the basis of testing data using a dynamic materials modeling. The maps exhibited two domains: the first at 950°C - 1100°C and strain rate higher than 0.1s-1, with a peak efficiency of power dissipation of 0.1, and the second at 950°C-1100°C and strain rate lower than 1s-1, with a peak efficiency of power dissipation of 0.4 and the strain rate of 0.01s-1. On the basis of microstructure observations, the first exhibits adiabatic shear bands, which called instability domain, the second represents fine recrystallized grain structures, which called stability domain. The optimal hot-working parameters are at 1050°C, 0.01s-1.

Effect of Heat Treatment to Ni-20wt.%Al Coating Diffusion

Ni-20wt.%Al coating was fabricated on the 6061-T6 aluminum alloy substrate in twin wire arc spraying technology. Heat treatment temperature was 400°C，480°C and 550°C, and each heat treatment time was 4h, 24h and 48h. Reaction mechanism and diffusion behavior of elements of coating/substrate interface were discussed. The XRD results showed that NiAl and Ni3Al phases were diminished and the nickel solid solution was gradually improved in volume. And some oxide phases existed, such as two types of alumina and nickel oxides. The SEM and EDS analysis showed, there was no obvious diffusion. At the low temperature condition, the diffusion phenomenon was existed in the interface.

Graphite Morphology Evolution during Melt Holding of Ductile Iron

Evolution processes of graphite morphology in ductile iron were investigated by quenching specimens during a long time holding of iron melt in a Ar atmosphere. Results show that spheroidal graphite is only observed at the early stage of melt holding. There are no evident changes in morphology of spheroidal graphite with increasing holding time up to 180 min. Subsequently chunky graphite precipitates directly after holding for 240 min as spheroidizing ability (Mg residual and RE residual) is insufficient. The number and size of eutectic chunky graphite cells increase with prolonged holding time. It should be noted that vermicular graphite forms around eutectic chunky graphite cells after holding for 360 min. When holding time reaches 420 min, graphite morphology is flake-like together with some chunky graphite. The graphite morphology in ductile iron changes from spherical to chunky, then chunky to vermicular, finally to flake with an increase in melt holding time. Both spheroidizing ability and numbers of effective nucleus decrease with prolonged holding time of melt, which affect graphite morphology.

Numerical Simulation of Dynamic Process under Low Pressure Casting Based on Two Phase Flow

It has been proved that the mold filling under low pressure casting can be described by the second order nonlinear differential equations characterized by damping oscillations. To obtain higher accuracy of the velocity field, the mold filling process with damping oscillations should be considered. A computational model taking the liquid level droping in the crucible into account based on two phase flow for filling process of damping oscillations is presented in this paper. Hydraulic simulation with the particle image velocimetry was adopted to verify the numerical simulation result. It is proved that the nemuerical simulation results used the presented model perfecly match with the particle image velocimetry results. Liquid level droping in crucible is the main reason for damping oscillations in mold filling. Velocity oscilations can be eliminated when the melt flow across a sudden expansion section. The detailed flow field based on the presented model can provide guidance to optimize the process parameters.

Research on Material Erosion Mechanisms of High Si-Al Alloy by Micro-EDM

This paper researches the material erosion mechanisms of high silicon- aluminum (Si-Al) alloy in micro electrical discharge machining (Micro-EDM). By using Quanta 200F environment scanning electron microscope, the microstructure of Al-50wt%Si alloy by spray forming was observed. And a simplified model of high Si-Al alloy was set up. The Al-50wt%Si alloy was machined by using copper electrode and tungsten electrode respectively. And the differences of surface morphologies and element energy spectrum were compared. The process and the material erosion mechanisms of high Si-Al alloy in Micro-EDM were analyzed in detail. The results may provide theoretical basis for Micro-EDM of high Si-Al alloy.

Research on the Process of High Silicon Aluminum Alloy in MEDM

Because of the high content of Si, traditional machining can hardly machine micro and small structures. While there is almost no microscopic force in the process of micro-electrical discharge milling (MEDM), so it has great advantages. In the process of MEDM for high silicon aluminum (Si-Al) alloy, the impacts of electrical parameters on processing time, the trend and degree of electrode wear are researched. The Al-50wt%Si alloy made by spray forming (SF) and casting forming (CF) and electrode of copper and tungsten are adopted to do the research. Related processing laws are summarized. A micro-3D structure was made by using appropriate parameters based on the experiment and research.

Investigation on over-Spray Powder of Spray Formed Al-22Si-5Fe-4Mn-3Cu-1Mg Alloy

Al-22Si-5Fe-4Mn-3Cu-1Mg alloy billet was prepared by spray forming processing, and the morphology and microstructure development of the over-spray powder were investigated in this paper. The results show that the diameter of the most powder was about 38um. With the decreasing of the powder size, its shape became more round and surface more smooth. Heterogeneous nucleation was the main nucleation way and the microstructures were dendrite grains for the most of over-spray powder. The formation mechanisms of the different microstructures were investigated through comparison with the microstructure of the spray formed ingot.

Interrelation between Microstructure and Mechanical Properties of Heavy Section Ductile Iron Casting

The microstructures and mechanical properties of a sector ductile iron casting with a wall thickness of 500 mm were investigated. Results show that spheroidal graphite is obtained in ductile iron, and chunky graphite is avoided because of chills used during solidification. Besides, the matrix structure is nearly a full ferrite structure at the edge of casting while some pearlite forms at the center of casting. The competing effect between graphite and matrix structure keeps the strength relatively inert to the change in solidification time or cooling rate, but these two parameters both impair elongation of ductile iron as well. The samples with full ferrite matrix exhibit a typical ductile fracture mode while those with some pearlite lead to a mixed ductile-brittle fracture mode. Graphite internal fracture or graphite/matrix interfacial cracking are two crack initiation sites.

Effect of Melting Process on Zr Content and Grain Refinement in ZE41A Alloy

The effects of melting process on Zr content and grain size in ZE41A alloy were investigated in this study. The results show that the soluble Zr increases with the increased addition content of Mg-Zr master, up to 0.87%. The ratio of Zr addition content to soluble Zr content changes within 3.86-4.8. The melt temperature has little effect on soluble Zr content. Grain size grows and both soluble Zr and total Zr decrease with the prolonged isothermal holding of the melt.