Papers by Author: Jian Zhong Cui

Abstract: Experiments show that high purity titanium (HP-Ti) samples have been successfully processed by equal channel angular pressing (ECAP) using a 120 degree die and a relatively slow ram speed at cryogenic temperature when the HP-Ti rods were trapped with 6061 Al alloy tubes. Optical microscopy (OM) and transmission electron microscopy (TEM) were utilized to investigate the deformed microstructure of the material. Typical microstructures of shear bands and deformation twinning were found in the deformed microstructure of ECAPed HP-Ti. Furthermore, the SAED pattern analysis of the twinning structures revealed that the deformation twinning occurred on {112} planes. Keywords: High purity titanium; ECAP; TEM; Deformation twinning; Cryogenic temperature.

Abstract: The new extrusion route of ECAP which is called route 135 was put forward in this paper. The grain refinement of the traditional extrusion route B_C and the new route of ECAP process in 99.9995% (5N5) high purity aluminum was compared using a die with a channel-intersection angle 90°. It was found through experiment that, the grain was very coarse in the cast ingot of 5N5 high purity aluminum, and the average grain size is about 60mm. High purity aluminum processed by one pass ECAP was refined notably, and average grain size is about 1000 μm. After two ECAP passes, the average grain size is 200μm with route B_C, while it is less than 50μm with route 135. The refinement of two passes of route 135 is equivalent to the refinement of eight passes of route B_C. It indicates that the route 135 is more effective than route B_C. TEM micrograph of 5N5 high purity Al with different ECAP pass under route B_C and route 135 was studied.

Abstract: Effects of hot extrusion processes on grain size of ZK60 alloy tubes was researched by combining numerical simulation with experimental research. The results show that grain size varies inversely as extrusion ratio and extrusion speed, with extrusion temperature being constant. In order to get the finer and homogeneous microstructure, higher extrusion ratio, higher extrusion speed and lower billet temperature should be chosen in the equipment's rated load. Isothermal extrusion is conducive to tube forming , and the smallest grain size and the better microstructure can be obtained at temperature of 300°C when other deformation conditions are constant.

Abstract: Grain refinement is quite important for producing 7050 alloy ingot especially in large scale. Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy Φ310 ingots and study the effect of electromagnetic field and grain refiner on the microstructure of 7050 alloy ingots. The results showed that both grain refiner and low frequency electromagnetic field can result in some grain refinement of 7050 alloy. However, the low frequency electromagnetic field shows more remarkable grain refinement. For the grain refined alloy by grain refiner, further significant grain refinement can be achieved with the application of low frequency electromagnetic field. The finest microstructure was achieved by combining the applications of both grain refiner and electromagnetic field.

Abstract: AZ80 magnesium alloy was semi-continuously cast under different physical fields which were conventional direct chill (DC) casting, low frequency electromagnetic casting (LFEC), ultrasonic casting (USC) and electromagnetic-ultrasonic combined casting (ECUC), respectively. The effect of different physical fields on solidification structures of AZ80 alloys was investigated. The results show that compared with the conventional DC casting, structures of AZ80 alloys billets cast with LFEC and USC have been greatly refined. The effective refinement takes place in the edge of billets when LFEC is applied. However, the effective refinement takes place in the center of billets when USC is applied. When combination of low frequency electromagnetic and ultrasonic fields is applied during semi-continuous casting AZ80 magnesium alloy billet, structures of AZ80 alloys are refined significantly in the whole billets everywhere and more uniform.

Abstract: Effect of different melt temperatures, holding time, cooling rate and C₂Cl₆ degasser treatment on the density of Mg-6Zn-0.5Y alloy was studied. The experimental results indicated that the density of RPT samples decreased with increasing of melt temperature, which indicating that the hydrogen content increased with the increment of temperature. And the results also showed that the density of RPT samples rapidly decreased at first and then decreased slowly with increasing of holding time, suggesting that the hydrogen content rapidly increased at first and then reached a saturated state with increasing of holding time. When cooling rate increased, the density of ingots gradually increased at the same melt temperature. When the melt was treated by 1%, 3% and 5% C₂Cl₆ degasser at 720°C, the density of ingots gradually increased compared with the ingot without treatment by C₂Cl₆ degasser. The density of ingot reached the maximum value when C₂Cl₆ degasser content was 3%, i.e, the ingot density value increased from 1.8649g.cm^-3 of the untreated sample to 1.8774g.cm^-3 of the sample treated by 3% C₂Cl₆ degasser, indicating that 3% C₂Cl₆ degasser treatment has an optimum degassing effect.

Abstract: Low-frequency electromagnetic casting (LFEC) processing could improve not only the metallurgical quality of magnesium billet including refining grain size, reducing regional microstructural difference and lightening segregation, but also its surface quality due to the effect of applied electromagnetic field according to the results by microstructure observation and the numerical simulation. In this research in-situ temperature measurement was carried out in LFEC processing in order to investigate heat transfer behavior of billet during solidification. The effects of the electromagnetic conditions (frequency and the intensity) together with the casting temperature on the sump and the mushy zone were investigated in detail. The results indicate that all the casting conditions affect the temperature field of magnesium billet markedly during solidification. Electromagnetic field could decrease not only the sump depth but also the difference of regional temperature field along the solidification direction leading to much more uniform cooling rate.

Abstract: Microstructures and Mechanical Properties of as-cast and extruded Mg–2wt.%Zn alloys containing dilute misch metal were investigated. RE additions were added in the form of relatively inexpensive cerium-rich misch metal (MM). The results indicate that the dilute MM addition has evidently effect the microstructure and mechanical properties of Mg-2wt.% Zn alloy. The grain refinement was improved and the amount of second phase precipitation was increased as increasing MM content in Mg-2wt.%Zn alloy from 0.2% to 1.5%, and the hardness determination and tensile test results show that the hardness of its ingot and the tensile strength of its extrusion rod were also enhanced, however, excessive MM addition would promote second phases forming network precipitating in grain boundary, which would result in the marked reduction of the plasticity of the alloy. Therefore, it is recommended that the MM content not exceed 0.6% in order to obtain high strength companying with relative higher elongation. The tensile properties of as-extruded Mg-2Zn-0.6wt.%MM alloy rod were UTS=266.7MPa, YS=213MPa, EL=14.5% which is similar to the corresponding properties of AZ31.

Abstract: Effects of low frequency electromagnetic field on surface quality, microstructure and hot-tearing tendency of direct chill casting of Φ500mm ZK60 magnesium alloy billets were investigated. The results show that with the application of the low frequency electromagnetic field, the surface quality of Φ500mm ZK60 magnesium alloy billets has been markedly improved, and the depth of cold fold is decreased. In the conventional direct chill casting, the microstructures of the billet, especially at the center, are coarse. The distribution of the grain size is non-uniform throughout the billet. From the edge to the center, the microstructure gradually changes from fine to coarse in all billets. However, under the low frequency electromagnetic casting, the microstructures of the billet is significantly refined, the distribution of the grains size is relatively uniform from the billets edge to the billets center. And it also shows that the hot-tearing tendency of direct chill casting Φ500mm ZK60 magnesium alloy billets under low frequency electromagnetic field is significantly reduced.

Abstract: Microstructures and macrosegregation of AZ80 magnesium alloy billets cast with and without the electromagnetic vibration were investigated. Compared with the conventional DC casting, microstructures of the billet have been greatly refined and the macrosegregation had been effectively reduced in electromagnetic vibration casting conditions. Increasing the electromagnetic vibration intensity, including both the stationary magnetic field and alternating magnetic field, leads to finer grains and more uniform distribution of solute elements in the billet.