Xuefeng Liu

A Novel Forming Process of Copper Cladding Aluminum Composite Materials with Core-Filling Continuous Casting

To simplify forming process of cladding materials with high performance, such as copper cladding aluminum composite materials, and to improve the interface quality of cladding materials, a novel forming process called Core-Filling continuous Casting (CFC) for bimetal composite materials is proposed. A conceptual equipment is developed, and the forming of composite bars of copper cladding aluminum is investigated. The basic technique theory of CFC, the reaction and bonded state of interface and the interfacial bonding strength of the cladding materials, as well as the influences of technological parameters are analyzed. The composite bars of copper cladding aluminum with 24mm in diameter of core material and 8mm in thickness of cladding layer are successfully fabricated. The results show that: (i) the proposed CFC process is feasible in principle; (ii) the composite bars of copper cladding aluminum having metallurgical bonding interfaces can be fabricated by CFC process under the conditions of liquid copper temperature of 1250~1300°C, liquid aluminum temperature of about 700°C and drawing velocity of 12~24mm/min; (iii) the copper layer thickness distribution is uniform both in the directions of portrait and circumference and (iv) the interfacial bonding strength is higher than that of core aluminum.

Analysis on the Deflection Angle of Columnar Dendrites of Continuous Casting Steel Billets Under the Influence of Mold Electromagnetic Stirring

In the current study, the deflection angle of columnar dendrites on the cross section of steel billets under mold electromagnetic stirring (M-EMS) was observed. A mathematical model was developed to define the effect of M-EMS on fluid flow and then to analyze the relationship between flow velocities and deflection angle. The model was validated using experimental data that was measured with a Tesla meter on magnetic intensity. By coupling the numerical results with the experimental data, it was possible to define a relationship between the velocities of the fluid with the deflection angle of high-carbon steel. The deflection angle of high-carbon steel reached maximum values from 18 to 23 deg for a velocity from 0.35 to 0.40xa0m/s. The deflection angles of low-carbon steel under different EM parameters were discussed. The deflection angle of low-carbon steel was increased as the magnetic intensity, EM force, and velocity of molten steel increased.

Experimental and Numerical Simulation of Surface Segregation in Two-Phase Zone Continuous Casting Cu–Sn Alloy

Surface segregation exists in two-phase zone continuous casting (TZCC) alloy with wide solid–liquid two phase zone. The surface segregation formation cannot be explained by the traditional solidification theories. ProCAST software was used to simulate the TZCC process for preparing the Cu–4.7 wt%Sn alloy with wide solid–liquid two phase zone. The Sn solute distribution in TZCC Cu–4.7 wt%Sn alloy was investigated, and the surface segregation mechanism of TZCC Cu–4.7 wt%Sn alloy was analyzed. The results showed that numerical simulation results were agreed with that of experimental. TZCC Cu–4.7 wt%Sn alloy in the center firstly started to solidify and resulted in “Λ” shape inclined solid/liquid (S/L) interface near the mold. Therefore, a narrow gap between the wall of the two-phase zone mold and the S/L interface formed. On the one hand, while Cu–4.7 wt%Sn alloy solidified along the opposite continuous casting direction, the solute redistribution between the solid and the liquid occurred, which lead to Sn solute decreased in solid and enriched in front of S/L interface. Because the narrow gap lies in front of inclined S/L interface near the two-phase zone mold, Sn solute enriches in liquid of the narrow gap. On the other hand, during the TZCC process, solid grains nucleate on the wall of the two-phase zone mold, while the melt feeds into the two-phase zone mold which the temperature is in the two-phase zone of the Cu–4.7 wt%Sn alloy. The solute redistribution also occurs while the solid grains grow, thus lead to Sn content increases in front of S/L interface near the wall of the two-phase zone mold. The enriched Sn solute is too late to diffuse, and will quickly flows into the narrow gap, resulting in further increasing of Sn content in the narrow gap. The liquid with enriched Sn solute in the narrow gap will become the surface layer after solidification, which lead to surface segregation layer during the TZCC Cu–4.7 wt%Sn alloy.

The Thickness Distribution of Oxidation Film on Tapered Pipe Surface in Dieless Drawing

The thickness distribution of oxidation film on the surface of AISI304 stainless steel tapered pipe, its influence factors, and the effect of metal matrix deformation on oxidation behavior during dieless drawing were studied in this paper. The results showed that oxidation rate was affected strongly by induction heating temperature and deformation degree. The thickness distribution of oxidation film was uneven and increased from the larger diameter end to the smaller diameter end along the axial direction of tapered pipe. When induction heating temperature raised or the distance between heat and cold sources was increased, or feed speed was decreased, oxidation rate was accelerated and oxidation film on the tapered pipe surface thickened significantly, due to massive cracks in oxidation film induced by deformation of metal matrix. The density and width of cracks in oxidation film were enlarged, and the thickness of oxidation film increased with the increase in deformation degree.

Numerical Simulation of Temperature Field and Microstructure of a Wide Copper Plate during Warm Mold Continuous Casting

Wide plates are mainly prepared through traditional cold mold continuous casting technology. A problem is cracking which caused by the non-uniform temperature field in solidification. Warm mold continuous casting is a new technology. Warm mold continuous casting of wide copper plate (section 500mm×12mm) was studies. Temperature field, solid/liquid interface and microstructure were analyzed by ProCAST software. By simulation, the optimal processing parameters: withdrawing speed was 60-80 mm/min, and the temperature of copper melt, mold and cooling water were 1200°C, 800-900oC and 20 oC, respectively. The temperature field in the width direction of the copper plate broad face was uniform, and the temperature decreased uniformly along the withdrawing direction. The temperature difference between center and edge was within 10 oC, and the temperature difference between narrow and broadfaces was within 25oC. Microstructure of plate contained ‘bamboo-like’ grains along the withdrawing direction.

Defect Formation Mechanism and Influence of Processing Parameters on Surface Quality of Copper Clad Steel Composite Wires Prepared by Core-Cladding Continuous Casting

Copper clad steel (CCS) composite wires with the carbon steel core diameter of 8 mm and copper cladding thickness of 1 mm were prepared by core-cladding continuous casting method under argon protection. The effects of melt temperature, molten metal height and drawing velocity on the surface quality were investigated. The formation mechanisms of the surface defects were discussed. The results showed that CCS wires with good surface quality could be continuously fabricated at a melt temperature of 1120 to 1200°C, a molten metal height of 2 to 4 cm and a drawing velocity of 10 to 30 mm/min. Raising the melt temperature, increasing the molten metal height or decreasing the drawing velocity is in favor of improvements in the surface quality. Insufficient supplement of liquid copper during solidification shrinkage resulted in surface dimple. Transverse hot cracking and exposed steel defect appeared because the frictional force between cladding metal and mold was larger than the tensile strength of cladding metal under high temperature.

Preparation and Fundamental Research of Continuous Through-Porous Pure Aluminum Flat Pipes by Depoling Continuous Casting

Continuous through-porous pure aluminum flat pipes were prepared continuously by a self-developed depoling continuous casting technology. An online measurement and control of mold temperature at free end of graphite core rods was realized, which was critical for the preparation. The quality of flat pipes was characterized. The results show that the flat pipes could be successfully prepared with the following process parameters: melt with temperature of 750 °C, cooling water with temperature of 20 °C and flow volume of 400 L·h-1, heat insulating mattress with thickness of 2 mm, mold temperature ranged from 635°C to 655°C and continuous casting speed ranged from 1 mm∙min-1 to 4 mm∙min-1. The flat pipe had cross-section dimensions of 14 mm×5 mm, which was aligned unidirectional pore diameter of 3 mm, pore number of 3 and smooth internal and external surface. The pore surfaces of flat pipes became smoother with the reduction of the graphite core rod surface roughness. When the surface roughness of graphite core rods was 0.531 μm and 0.124 μm, the corresponding surface roughness of pores was 0.581 μm and 0.184 μm, respectively. The mold temperature at the free end of graphite core rods was kept at a low thermal temperature range which was 5~25 °C lower than the solidification point of pure aluminum that is necessary for stable depoling continuous casting.

Research on Dieless Drawing Process of Stainless Steel Tapered Tube

The traditional forming technologies of stainless steel tapered tube have some disadvantages, such as its complicated processes, few product specification, low production efficiency and high production cost. Dieless drawing is a new kind of near net-shaping process for fabricating tapered metallic tubes with large deformation per pass, high yield ratio of material and flexible production. Dieless drawing of stainless steel tapered tube was studied systematically in order to establish both temperature field model with respect to the changes of boundary condition and metal flow velocity during deformation, and a drawing speed controlling model with respect to the volume change of deformation zone. The models were verified by experiments in the present investigation. Finally, a continuous pickling process with variable-speed was proposed for tapered metallic tube, which was successfully applied to surface oxidation film removal of the stainless steel tapered tube.

Preparation and Mechanism of Cu/Nano-TiO2/PBO Composite Fibers by Photocatalysis Electroless Plating

Cu/nanoTiO2/PBO composite fiber with low density, high strength, toughness and conductivity was prepared with a photocatalysis electroless plating method by reduction depositing Cu2+ on the surface of nanoTiO2/PBO composite fiber. The process parameters on the preparation of Cu/nanoTiO2/PBO composite fiber were optimized by the characterization of surface morphology, phase, composition, pull-out strength and resistivity of Cu/nanoTiO2/PBO composite fibers using SEM, XRD, EDS, electronic tester of tensile strength and multimeter, respectively. The mechanism of Cu coating nanoTiO2/PBO composite fiber was also discussed in this study. The results showed that Cu/nanoTiO2/PBO composite fibers were well prepared under the bath composition of CuSO45H2O 16gL-1, KNaC4H4O64H2O 15 gL-1, Na2EDTA2H2O 24 gL-1, HCHO 16 mlL-1, NaOH 14 gL-1, C10H8N2 24 mgL-1 and K4Fe (CN)6H2O 12 mgL-1 by the UV-light irradiated for 30 min. The diameter, pull-out strength and resistivity of Cu/nanoTiO2/PBO composite fiber were 20.2 μm, 2.25 GPa and 0.02864 Ωmm2m-1, respectively. Cu2+ ions on the surface of nanoTiO2/PBO composite fiber were reduced to Cu by photo-electrons which were generated of nanoTiO2 under the UV-light irradiated, and the primary Cu layer as a catalytic center promoted the reduction reactions of producing Cu/nanoTiO2/PBO composite fiber further.

Preparation and Mechanism of Nano-TiO2 Coatings on Poly(p-phenylene-benzobisoxazole) (PBO) Fiber

nanoTiO2/PBO composite fiber was prepared with a chemical method by depositing nanoTiO2 on the surface of PBO fiber which was treated by silane coupling agent. The process parameters on the preparation of nanoTiO2/PBO composite fiber were optimized according to the interfacial adhesion between the composite fiber and epoxy resin, and the coating mechanism of nanoTiO2/PBO composite fiber was also discussed. The results show that the uniform nanoTiO2/PBO composite fiber with high interfacial adhesion can be prepared on the PBO fiber which was pretreated by silane coupling agent with a concentration of 1.5 % for 35 min at room temperature, in which the nanoTiO2 aqueous solution with a concentration of 1.0wt% was ultrasonic dispersed for 1h in alkaline environment (pH 11), and then the PBO fiber was immersed in the dispersed solution at 60 °C for 6 h to prepare nanoTiO2/PBO composite fiber. The single fiber pull-out strength of the prepared composite fiber was increased by 85.28 % compared with that of the untreated PBO fiber. Silane coupling agent was a bridge of PBO and nanoTiO2, hydrogen bond association and like dissolves like were attributed to the improvement of interfacial adhesion between nanoTiO2 and PBO fiber.