Papers by Author: Yue Long Bai

Abstract: An advanced method called internal electromagnetic stirring (I-EMS) was investigated to resolve the engineering problems like coarse-grain, inhomogeneous structure and macrosegregation. The electromagnetic stirrer functioned with internal-cooling was inserted in the melt during DC casting. In this study, a round billet of 2219 alloy DC cast with a diameter of 880mm under I-EMS process condition was produced, and its structure and composition distribution were comparatively characterized. The results show that the mean grain size decreased from the range of 872, 1023, 332 μm to the range of 317, 438, 271 μm at different billet positions with I-EMS. I-EMS consequently produce superior grain refinement and homogeneity. The effect of I-EMS on the grain-refinement and macrosegregation was also discussed.

Abstract: High volume fraction SiC/Al composite material, with its excellent thermal properties and flexible preparation process, has been widely used in the field of electronic packaging. In the paprer, the development of SiC/Al materials for electronic packaging and their preparation methods are reviewed. The preparation processes for preparing SiC/Al by liquid infiltration are mainly introduced. The advantages and disadvantages of several important processes are analyzed. Finally, the development trend of SiC/Al for electronic packaging prepared by liquid infiltration is prospected.

Abstract: The high-strength Al-Zn-Mg-Cu alloy has broad application prospects in high-end equipment manufacturing fields, such as aerospace, national defense and military industry, and transportation. However, the grains of Al-Zn-Mg-Cu alloy are coarse, and the grains further grow after heat treatment, which seriously reduces the mechanical property of alloy castings. Therefore, the study on reducing the grain size of the cast alloy was carried out by adding Zr element and applying electromagnetic stirring treatment technology, as well as suppressing the recrystallization of the aluminum alloy during the heat treatment process. The results show that adding Zr element reduced the grain size by 30%, the tensile strength increased by 50 MPa, and the elongation increased by more than 10%.

Abstract: High-strength aluminum alloy with large-scale and thin-walled complex castings have broad application prospects in aerospace, weapons, electronics, defense and military industries. However, due to the uneven thickness of the plate, the casting defects are inevitable by the ordinary casting method, and it is impossible to accurately control the shape and performance of the casting in the casting process. Previous studies have found that the semi-solid rheological extrusion casting technology with short process and near-end type can help solve this technical problem. Therefore, this paper studies the semi-solid rheological extrusion casting process of thin-walled complex casting of ZL114A aluminum alloy. The combination of numerical simulation and experimental research is used to simulate and optimize the filling and solidification process of thin-walled specimens. Based on this, a semi-solid rheological extrusion casting test was conducted. The result showed that, (1) The optimized model can well reflect the filling and solidification process under different rheological extrusion casting parameters, and obtain defect-free castings through process optimization. (2) The thin-walled parts of the thin plate casting produced by semi-solid rheology extrusion have excellent mechanical property and ductility.

Abstract: A layered composite structural model with an outer wear-resistant layer of high-silicon aluminum alloy and an inner layer of ultra-high strength aluminum alloy is designed. A scaling brake drum part with layered composite was prepared by semi-solid precision forming process. The effects of process parameters such as casting temperature, specific pressure, solid layer temperature and heattreatment system on the composite interface were investigated. The results show that the casting temperature and solid layer temperature had a great influence on the interface recombination. The high forming specific pressure could effectively restrain the growth of secondary dendritesof the composite, and the proper heat treatment process could improve the morphology of the composite interface. A scaling brake drum component with A390/7050 layered composite structure was well prepared under optimal conditions.

Abstract: The microstructure and mechanical properties of 7050 alloy rheo-castings after treated by Annular Electromagnetic Stirring (A-EMS) melt treatment were investigated. The results revealed that, under A-EMS, the refinement and homogeneity of the solidification structure could be improved greatly and the slurry was suitable for the following rheo-casting; and also the hot-cracking defects in the casting process were significantly alleviated, meanwhile, the strength and ductility of the alloy casting were found to be comparable to those of conventionally forged 7000 series alloys.

Abstract: Semi-solid thixoforming process was applied to produce track shoe of 15%SiCp/2A14 composites. The thixoforming process optimization was simulated by using Deform 3D software. The effects of forging pressure, slug size and reheating temperature on formability of track shoe were investigated. The results showed that a track shoe with better integrity was prepared by optimizing the process, and its microstructure and mechanical properties could meet requirements.

Abstract: With high module, high strength and good isotropy, SiCp/Al composite has been widely applied in the fields such as airspace, transportation vehicle and electronic packaging. Stir casting process with advantages of low cost, high efficiency and near-net shape has become a main production method, but the two-phase flow behavior of the SiCp/Al composite during casting process has greatly effect on particle distribution and ultimate properties of casting. In this work, a two-phase flow computational model was developed, and the filling flow process of SiCp/A357 composite based on a benchmark test die was numerically simulated with commercial software Fluent. The effects of SiCp volume fraction and SiCp size on the flow field of SiCp/A357 composite were investigated. The results showed that there existed difference of flow fields between A357 alloy and SiCp/A357 composite, and the simulation results would be helpful to optimize the casting process.

Abstract: The application of Annular Electromagnetic Stirring (A-EMS) for production of high-quality slurry has been examined. Al-11%Zn-3%Mg-1%Cu-0.13%Zr alloy was used to investigate the effect of A-EMS at various temperatures above liquidus on structure refinement. The results indicate that the grain size was reduced greatly and the homogeneous structure was achieved. Instead of the case in tradition, the nucleation particles gradually formed and the enhanced grain refining efficiency can be mainly attributed to an instantaneous nucleation of numerous heterogeneous nucleation of Al₃Zr in the superheating melt under A-EMS.

Abstract: The effects of annulus gap width, stirring power and stirring frequency on the microstructure of the semi-solid A356 aluminum alloy slurry have been investigated by the annulus electromagnetic stirring (AEMS) technology The results show that narrow annulus gap , strong stirring power and high stirring frequency are advantageous to obtain the small spherical primarymicrostructure, the smaller the annulus gap width is, the bigger the stirring power is, and the higher the stirring frequency is, the more uniform, the smaller and the more spherical the microstructure is. So the high stirring frequency, narrow annulus gap, strong stirring power are beneficial to obtain the fine and spherical semisolid microstructure in AEMS. Also the results indicate that the primary particles are globular, small and distribute homogeneously in the AEMS.