Papers by Author: Qing Feng Zhu

Abstract: In this study, a purity of 99.995percent high purity aluminum was multi-directionally forged up to a maximum cumulative strain of 4.5 at room temperature. The macro and micro structure evolution in the multi-directionally forge process was investigated by structure observations and hardness measurements. The results show that the inhomogeneous deformation of multi-directional forging results in that the structure and hardness is quite different between the easy deformation zone and stagnant zone. Dynamic recrystallization occurs in easy deformation zone of high purity aluminum sample at room temperature as the cumulative true strain is 1.5 (3 forging passes), while the structure in the stagnant zone is still not recrystallizated even at a cumulative true strain of 4.5 (9 forging passes). The recrystallized grain size in the easy deformation zone is reduced with the number of forging passes, and the area of recrystallize grains increase with the number of forging passes.

Abstract: Commercial aluminum ingot with the diameters of 100 mm is produced by conventional out-phase electromagnetic field HDC casting process. The out-phase electromagnetic field is applied on the HDC casting process. The effect of out-phase electromagnetic filed on the ingot surface and structure is investigated. The result shows that the out-phase electromagnetic field is more effective in improving the upper surface, while, has little function on the bottom surface. The macro/microstructure of the ingot is changed by the out-phase electromagnetic field. Very long and coarse columnar grains evolve to short and thin columnar grains with the application of the out-phase electromagnetic field.

Abstract: 7075 aluminum alloy ingot with the diameters of 100 mm was produced by Horizontal Direct-Chill (HDC). The temperature in the melt was measured and the ingots were examined in detail with the aim to reveal the floating grains in the HDC ingot. Experimental results show that very large floating grains with coarse dendrite arm spacing (DAS) mainly concentrate in the half-moon area near bottom surface of the HDC casting ingot, under the function of gravity. The floating grains in the HDC casting process is much bigger than that founded in Vertical Direct-Chill (VDC) casting process.

Abstract: During the low frequency electromagnetic casting process, the electromagnetic parameter plays an important role among the casting parameters. In this work, effects of electromagnetic parameters on the electromagnetic field and body force are analyzed by constructing a two-dimensional finite element model and using ANSYS software which is a kind of commercial FEM analysis software. The results show that the current frequency mainly influences the distribution of electromagnetic body force, the current intensity determines the intensity of electromagnetic body force, and the current frequency and intensity should be matched during the low frequency electromagnetic casting process.

Abstract: Low frequency electromagnetic (LFE) field was applied during the conventional hot-top casting process. Thermocouples were used to measure the cooling curves from the border to the center of the ingot during steady-state of casting process, cooling curves were obtained, and effects of low frequency electromagnetic field on the solidification, macrostructure during the conventional hot-top casting for 6063 aluminum alloy process were analyzed. The experimental results show that the forced convection caused by the low frequency electromagnetic (LFE) filed can make the melt temperature uniform, promote the evacuation of superheat, make the temperature in the liquid pool lower than the liquidus temperature of 6063 aluminum alloy, increase the number of floating nuclei, make the ingot with fine and homogeneous macrostructure, though there is no addition of any grain refiners.

Abstract: 7075 aluminum alloy ingot with the diameter of 100 mm has been produced by horizontal direct chill casting in different casting speed. The effect of casting speed on the sump profile and the ingot surface quality was studied by sump profile observation. It was found that increasing the casting speed results in the deepening of the liquid pool, the adding of segregation knots and the reducing of cold shouts in the ingot surface. It is also found that the depth of the liquid pool is directly proportional to the casting speed and the squared radius of the ingot.

Abstract: On the basis of conventional hot-top casting, low frequency electromagnetic field was applied in the process of hot-top casting to produce 7050 aluminum alloy ingot, the influences of low frequency electromagnetic field on cold-shut have been studied. The experimental results show that under the effect of the low frequency electromagnetic filed, the depth of cold folding has been decreased, and the as-cast structure has been refined. The reasons for low frequency electromagnetic field improving the surface quality, refining the structure of the ingot were summarized.

Abstract: On the basis of conventional level casting, low frequency electromagnetic field is applied during conventional level casting process. Effects of low frequency electromagnetic field on melt flow, macrostructure and microstructure have been studied. The experiment is performed on the Al-4.5% Cu alloy, and the experimental results show that with the application of the low frequency electromagnetic field, the macrostructure and microstructure are changed greatly. The reasons for the low frequency electromagnetic field changing the macrostructure and microstructure of the ingot were summarized.

Abstract: The influence of different electromagnetic fields on the horizontal direct chill (HDC) casting of aluminum alloy is studied. 7075 aluminum alloy with 100-mm in diameter is produced by HDC casting process; single electromagnetic field located before or around the mold and an out-phase electromagnetic field (OPEMF) are applied in the HDC casting process. The effect of different electromagnetic fields on the HDC casting solidification behavior and as-cast structure is investigated. The electromagnetic field can effectively make uniform thermal distribution in the molten pool and refine the as-cast structure. The OPEMF is more efficient than the single electromagnetic field in improving the as-cast structure of HDC cast ingots.

Abstract: Hot tear is one of the main defects during the aluminium casting process, and it usually occurs during solidification. In this work, the low frequency electromagnetic field was applied to study the effects of low frequency electromagnetic field on hot tear during the conventional hot-top casting process. The results show that under the effect of the low frequency electromagnetic field, the structure of the ingot is refined, the flow direction is changed, and the depth of the sump becomes shallow. All these factors can decrease the hot tear susceptibility.