Advanced Materials Research Vols. 652-654

Abstract: An experimental measuring method of flight trajectory of edge electron of the electron-beam in the electron gun of furnace was designed. Intermediate perforated copper foil plate is placed in parallel at a key position within the electron gun. The theoretical beam diameter of the electron beam which is reaching the position can be obtained through measuring pore diameter in copper foil plate left after being broke down by the electron-beam, so experimental data got can be verified the theoretical results.

Abstract: The concept of maximal and minimal displacement value of the electron-beam was proposed considering the influence of space charge effect based on the displacement value of the electron-beam in the process of magnetic deflection scanning in the ideal condition. The deduction of mathematical model of the maximal and minimal displacement value was accomplished. The position of the beam spot can be more accurately controlled by the model, thus it is made sure that un-molten metal is bombarded by the beam spot accurately, which can increase the melt quality.

Abstract: In this study, 7050 aluminum alloy strip was produced using the twin-roll casting technique. Microstructures and properties of the cast-rolling 7050 aluminum alloy were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Vickers hardness test. The results indicate that microstructures of cast-rolling 7050 alloy strip are inhomogeneous on the cross section. From the edge to the center, the size of grain decreases gradually and becomes more homogeneous, showing a transition from dendrite grains to equiaxed grains. There are undissolved second phase particles in grains and at grain boundaries. And the dendrite grains and second phase particles can be reduced by solution treatment, and the hardness of the cast-rolling strip can be improved by aging treatment.

Abstract: It is important to strictly maintain the cooling rate in producing thin wall ductile iron (TWDI) to prevent carbide formation. There are many ways to control cooling rate whereas casting design is the most independent one. This paper discusses the effect of gating system design on microstructure and mechanical properties of 2 mm TWDI plate. A casting design based on vertical gating system is made to produce TWDI plates with the thickness of 1, 2, 3, 4, and 5 mm. This vertical system allows plates to function as runner. This situation helps in preventing premature solidification. There are three designs in which they are coded as T1, T2, and T3. These three designs were also used in making 1, 3, and 5 mm TWDI plates of which the result has been published. Z-Cast is used to conduct a casting design simulation for filling flow and solidification. The result of flow simulation shows that the filling flow is resulted in two kinds. The result of solidification specifies that in T1 and T2 the 2 mm TWDI plates solidify in the same time as 1 mm TWDI plate. Furan sand was used as moulds in the experiment. The result of the experiment highlights that in all of the designs, which have microstructure and consisted of nodule graphite in ferrite matrix, no trace of carbide and skin effect are formed. The length of skin effect varies in all of the designs. The highest nodularity is only 86% while nodule count is 1344 nodules/mm2. Brinell hardness number for all of the design is beyond the standard given by JIG G5502. As for UTS and elongation none of the designs exceeds the minimal standard. The result of the experiment does not confirm the result of the simulation. In sum, compared to the previous result, the curve trends of 2 mm TWDI plate combine the curve trends of 1 and 3 mm TWDI plates.

Abstract: The semi-solid billets of AlCu4.5Mn0.8 alloy were cast respectively by low frequency electromagnetic, low-superheated, and conventional direct chill casting. The effect of casting processes on microstructures was investigated. The results show that due to the effect of the low frequency electromagnetic field, the coarse dentritic microstructure is gradually broken up and turned into the homogeneous, fine rosette-shaped non-dentritic microstructures with the increase of electromagnetic frequency from 10 Hz to 30 Hz. When electromagnetic frequency is 30 Hz, the homogeneous, fine non-dentritic microstructure what is suitable for semi-solid reheating and thixo-forming could be obtained successfully.

Abstract: The influences of different pulse voltage and mold temperature on solidified structure of 6061 alloy under low-voltage pulsed magnetic field (LVPMF) were studied. The results show that grain of 6061 alloy can be refined greatly by LVPMF treatment. The dendrite growth is restrained and the microstructure is changed from larger dendrite grains to smaller nondendritic grains. When the pulse voltage is at 0V-300V, grain size of the alloy decreases as pulse voltage increases, and the primary phase degrades from developed dendrites into rose-like or spherical crystals. When the mold temperature is at 20°C-600°C, the decrease of mold temperature enhances the refinement effect of LVPMF processing. With the decrease of the mold temperature, grain size of the alloy decreases.

Abstract: 7075 aluminum alloy melt conditioned by annular electromagnetic stirring(A-EMS) was cast in the TP1 mould, and the effects of pouring temperature, stirring current, stirring frequency and annular gap width on microstructures were analyzed. The A-EMS process exhibits superior grain refinement and remarkable structure homogeneity compared with conventional casting(N-EMS) and conventional electromagnetic stirring casting(EMS). With the increasing of the pouring temperature, the microstructures of the sample conditioned by A-EMS are inclined to become coarse and non-uniform compared with which have the more serious inclination conditioned by N-EMS. With the stirring current or stirring frequency increasing, the rosette-like or dendritic primary α(Al) phase decreases significantly on the sample microstructures, and the non-dendritic primary α(Al) phase is finer and more spherical. Narrow annular gap is advantageous to obtain uniformly fine spherical solidification microstructures.

Abstract: In this paper, the effect of magnetostatic field on the microstructure and microsegregation of 7075 aluminum alloy strip by twin-roll casting is researched , and the result shows that when no electromagnetic field is applied during the process of roll-casting , the microstructure of 7075 strip is most composed of coarse columnar and dendritic crystal , the direction of grains is equal to roll-casting direction. When the magnetostatic field with 0.13T intensity is applied during the twin-roll casting, the microstructural of strip becomes uniform ,refined and equiaxed at the central zone of strip, and the dendritic crystal at the surficial is disordered and refined significantly.

Abstract: The changes of roll casting microstructure under different casting conditions on experimental casting machine was studied, which showed that solidification microstructure is different with different casting speed and thickness. When the casting speed is 1.3m/min,the thickness of strip is 6mm, coarse columnar grain dominates the solidification structure; when it continuously increases to 4m/min, the thickness of strip is 3mm, aluminum strip shows as hybrid organization with columnar grains in two sides and small equiaxed grains in the center; when the casting speed is over 12m/min,the thickness of strip is 1.75mm, columnar grains all convert into equiaxed grains in solidification structure. The deformation microstructures are different with the different casting speed and thickness of strip. When the casting speed is 0.9m/min, the thickness of strip is 6mm, typical processing flow lines come into being along longitudinal direction and transverse direction shows as squashed grains without re-crystallization. When the casting speed is 5.4m/min, the thickness of strip is 2.5mm, microstructure of aluminum strip becomes chevron organization from columnar crystal, there is a condensate in the center of aluminum strip, and the deformation of outer metal is more serious than inner, incomplete dynamic recrystallized grains come into being in the outer metal of the aluminum strip.

Abstract: In this paper, the directional solidification microstructure of Bridgman system was simulated using phase-field method, and different calculated results were obtained with four pulling velocities. When the pulling velocity is 0.06 cm/s, the columnar crystals competitively grow in the initial stage, and have a necking phenomenon in the last stage. When the pulling velocity is 0.04 cm/s, the columnar crystals become thinner and competitively grow all the time, and the microsegregation is bigger. When the pulling velocity is 1.00 cm/s, planar interface comes back, and solute trapping takes place. The columnar crystals become much thinner, and microsegregation decreases. When the pulling velocity is 3.00 cm/s, the grain boundary of columnar crystals becomes unconspicuous, and the degree of microsegregation approaches 1.