Papers by Author: Zhi Feng Zhang

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: Large-sized 2219 aluminum alloy ingot has wide application prospect in aerospace and military fields. Severe defects, such as coarse grain, the inhomogeneity of structure and macrosegregation occurred in large-sized aluminum ingot produced by normal DC casting. The application of a single magnetic field in DC casting process cannot solve these defects. In this paper, a new method with the combination of electromagnetic fields imposed on bulk melt treatment during DC casting was proposed. And a φ508 mm ingot of 2219 aluminum alloy was prepared in this method. Compared with the normal DC casting, the effect of the combined electromagnetic fields on the microstructure and properties was studied. The experimental results demonstrate that the application of the combined electromagnetic fields significantly refines the grains, and the grain size distribution on the cross section of the ingot tends to be more uniform as well as the mechanical properties are significantly improved. The microstructure and grain size distribution can be significantly affected by different combined electromagnetic fields. It is considered that the appropriate combined electromagnetic fields parameters play an important role in controlling the homogeneity of large-sized ingots.

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: To obtain fine microstructure and homogeneous distribution of alloying elements in the large-sized billet, the internal electromagnetic stirring as a new electromagnetic stirring method was proposed and utilized for the preparation of Ф508 mm 7050 aluminum alloy billet. The results demonstrate that the internal electromagnetic stirring could refine the microstructure and second phase, and alleviated the macrosegregation significantly. The grain size at the edge, 1/2 radius, and center of the billet decreased to 180 μm, 175 μm, and 185 μm, respectively. Moreover, the relative macrosegregation of Zn, Mg, and Cu at the edge and center decreased to 3.9% and 2.8%, 2.3% and 1.6%, 4.1% and 2.5%, respectively.

Abstract: Uniform direct chill (UDC) casting is coupled annular electromagnetic stirring and intercooling, having been utilized for the preparation of large-sized aluminum alloy billet. In this paper, the UDC casting was applied to 2A14 aluminum alloy billets with a diameter of 584 mm. Hot compression tests, cogging and ring rolling procedures were carried out for the billets, respectively. The results show that during the deformation temperature of 420 °C and the strain rate of 0.01 s⁻¹ to 10 s⁻¹, the flow stresses of different positions are higher and more stable in the UDC casting billet than in the normal direct chill (NDC) casting billet. The dislocation glide is the dominant deformation mechanism of 2A14 aluminum alloy. Meanwhile, the UDC casting significantly improves the mechanical properties of the rolled rings in tangential and axial directions compared with the NDC casting.

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: Stir casting is a near net shape process that can cast the composite components directly. Fluidity is an important factor for mold filling in casting process, but the fluidity of composite slurry is poor due to the addition of SiCp. In this research, SiCp/A357 composites with 20wt.% SiCp were manufactured by mechanical stir casting. Effect of mechanical stirring and air pressure on the fluidity of SiCp/A357 composites were investigated with eight thin flow channels. The fluidity was compared at different rotating speed and air pressure. The results showed that the fluidity increased with rotating speed, which was more obvious in semi-solid interval. It was noticed that the fluidity decreased with air pressure, the gas involving and the cooling speed were aggravated with air pressure increasing, which reduced the fluidity.