Papers by Author: Jin Gang Qi

Abstract: In the unmodified and EP-modified melt of Q235 steel, the solidification behavior including the nucleation and growth of crystals has been observed in situ by use of a confocal scanning laser microscope combined with an infrared image furnace, and meanwhile, described the characteristic of phase transformation. The result shows that the every stage of phase transformation is advanced; the phase transformation time is shortened, and temperature is reduced during heating proceeds. On the other hand, it can be observed that the nucleation density of solid phase increases and has an even distribution among the liquid phase.

Abstract: Hypereutectic Al-Si alloy are desirable and promising for many structural applications. The influences of electric pulse parameters on Al-22%Si-1.5%Cu alloy by using OM (optical microscope) analysis along with wear test had been investigated. This work focused on studying the comparison of its solidification structure and wear resistance property with and without electric pulse treatment, respectively. The results indicated that EPM (electric pulse modification) treatment with different voltage parameters along with the frequency parameters both had the remarkable effects on micro-structure, and the grain size of alloy was refined gradually with the increase of pulse voltage or frequency. The wear resistance property of the alloy was enhanced by electric pulse treatment. It was observed from DSC cooling curve that the precipitation peak point of primary silicon was delayed by electric pulse modification comparing to the original sample without electric pulse treatment, which was analyzed to play a critical key in the alloy grain refinement.

Abstract: The influence of different broaching rate, the training of thermo-mechanical cycle and Electro-pulse Modification (EPM) on the shape memory effect of the FeMnSiCr alloy was investigated. The recovery pulling force can be realized as high as 22850N after EPM treatment. The Fe-based shape memory alloy (SMA) pipe joint can meet the requirement of engineering application.

Abstract: It was investigated that the effect of electric pulse modification (EPM) on the hot tearing of Al-5%Cu-0.8%Mn alloy. The results indicate that hot tearing tendency of all samples can be reduced treated by electric pulse with different parameters, moreover, hot tearing stress of alloy with EPM was enhanced 3 times or so than that of samples without treatment. Decreasing the quantity of eutectic in grain boundaries, decreasing the end-solidifying temperature of the alloys, and refining the grains are main causations for increasing hot tearing resistance of Al-5%Cu-0.8%Mn alloy by electric pulse modification.

Abstract: It was investigated that the effect of electric pulse modification (EPM) on the hot tearing of Al-5%Cu-0.8%Mn alloy. The results indicate that hot tearing tendency of all samples can be reduced treated by electric pulse with different parameters, moreover, hot tearing stress of alloy with EPM was enhanced 3 times or so than that of samples without treatment. Decreasing the quantity of eutectic in grain boundaries, decreasing the end-solidifying temperature of the alloys, and refining the grains are main causations for increasing hot tearing resistance of Al-5%Cu-0.8%Mn alloy by electric pulse modification.

Abstract: The melt of nonleaded free-cutting brass is modified by the electric pulse and the effects on the solidification structure and properties of Silicon Brass are studied with different Bi contents and under different pulse parameters. The results show that the varieties of Bi contents and pulse parameters have a greater impact on grain size and microstructure uniformity of the brass. After silicon brass with 0.5% Bi is modified by electric pulse, the Bi grain size is reduced to 5μm from 30μm, and its shape is changed into being granular from worm-like or long-strip-like, distributed more evenly in α phase and α phase boundary, and a few of which goes into the β phase matrix.

Abstract: In order to improve toughness of the weld heat affected zone (HAZ) of ultra-fine grained (UFG) steel, a thermal simulation procedure of Fe-Mn-Si UFG steels with different Al addition was conducted and the corresponding microstructure was characterized and investigated. The results indicate that the maximum value on driving force of nucleation is ultra-fine grain steel with wtAl=0.6%, it has been explained in Nucleation kinetics that the grains are fine in UFG2. On the other hand, the bainite ferrite growth orientation has been increased. The toughness was remarkably enhanced in the steel welded heat affected zone. The formation of strie retained austenite and grain refinement of bainite ferrite in Fe-Mn-Si UFG steels with Al additions results in the increasing toughness of weld HAZ.

Abstract: It is not difficult to prepare self-compacting concrete (SCC) in laboratory now. The problem researchers faced is how SCC can be popularized in civil engineering. A modified densification mixture design algorithm (DMDA) is used in this study to prepare the control mixture. And on the basis of the system analysis for exist studies, 6 factors are chosen as experimental factor and 25 experiments are designed by orthogonal design experiment method. The results analysis indicates that only 3 factors are significant on SCC and their recommend value is obtained respectively. It may shed light on the application of SCC.

Abstract: In this paper, the effects of electric pulse on solidified structure and graining process of near eutectic Al-5%Cu alloy have been investigated during solidified process. It was treated with different pulse voltages at 740°C in this experiment, and established the cooling curve. The results show that the improvement of alloy casting macro-segregation and solidification structure refinement by electric pulse discharging; The change of the solidified casting structure has a preferable coincidence relation with the change of the cooling curve, and analysis of the cooling curve shows that the best granular effect has a maximal supercooling on the curve.

Abstract: Taking the hypereutectic Al-Si alloy as the research object, the fading characteristics of Al-22% Si alloy at different pulse temperatures are investigated in this paper in order to analyze the mechanism of electrical pulse modification to the alloy. We can get the conclusion by observing the microstructure of the sample, measuring the microhardness and calculating the volume fraction and the average size of primary silicon: at different pulse temperatures, the effect of electric pulse modification is fading with static duration prolonging; meanwhile, with the temperature upward, the modification effect and fading trends to be weak, which indicates the best pulse temperature is one of the important factors to influence the modification effect.