Li Tingju

Removal of boron from metallurgical grade silicon by electromagnetic induction slag melting

Abstract A new purification process was developed to remove impurities in metallurgical grade silicon (MG-Si) by electromagnetic induction slag melting (EISM). Vacuum melting furnace was used to purify boron in different slag systems. The results show that the removal effect in SiO2-CaO-Al2O3 systems is better than that in other slag systems by EISM. The boron content in MG-Si is successfully reduced from 1.5×10−5 to 0.2×10−5 during EISM at 1 823 K for 2 h. Meanwhile, Al, Ca and Mg elements in MG-Si are also well removed and their removal efficiencies reach 85.0%, 50.2% and 66.7%, respectively, which indicates that EISM is very effective to remove boron and metal impurities in silicon.

Wear behavior of high strength and high conductivity Cu alloys under dry sliding

Abstract In order to study the wear behavior of different kinds of contact wires, the dry sliding wear behaviors of Cu–Sn, Cu–Ag and Cu–Mg alloys prepared by up-drawn continuous casting and followed continuous extrusion were studied. The research was tested on a block-on-ring wear tester. The results indicate that the friction coefficient is remarkably influenced by the formation of a continuous tribofilm, which consists of oxidation film. The abrasion, adhesion, oxidation and plastic deformation are observed. Oxidation and abrasion wear mechanisms dominate at the lower sliding velocity and load. The combination of oxidation and adhesion play leading roles with the increasing load and velocity. Plastic deformation is detected under higher applied load and sliding velocities.

Motion behavior of non-metallic particles under high frequency magnetic field

Non-metallic particles, especially alumina, are the main inclusions in aluminum and its alloys. Numerical simulation and the corresponding experiments were carried out to study the motion behavior of alumina particles in commercial pure aluminum under high frequency magnetic field. At the meantime, multi-pipe experiment was also done to discuss the prospect of continuous elimination of non-metallic particles under high frequency magnetic field. It is shown that: 1) results of numerical simulation are in good agreement with the experimental results, which certificates the rationality of the simulation model; 2) when the intensity of high frequency magnetic field is 0.06 T, the 30 μm alumina particles in melt inner could migrate to the edge and be removed within 2 s; 3) multi-pipe elimination of alumina particles under high frequency magnetic field is also effective and has a good prospect in industrial application.

Effect of immersion Ni plating on interface microstructure and mechanical properties of Al/Cu bimetal

Abstract A nickel-based coating was deposited on the pure Al substrate by immersion plating, and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450–550 °C. The interface microstructure and fracture surface of Al/Cu joints were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of the Al/Cu bimetals were measured by tensile shear and microhardness tests. The results show that the Ni interlayer can effectively eliminate the formation of Al-Cu intermetallic compounds. The Al/Ni interface consists of the Al 3 Ni and Al 3 Ni 2 phases, while it is Ni-Cu solid solution at the Ni/Cu interface. The tensile shear strength of the joints is improved by the addition of Ni interlayer. The joint with Ni interlayer annealed at 500 °C exhibits a maximum value of tensile shear strength of 34.7 MPa.

Separation efficiency of alumina particles in Al melt under high frequency magnetic field

The effects of separation time and magnetic induction intensity on the separation efficiency of alumina particles with diameters varying from 30 to 200 μm in aluminum melt were investigated. The experimental results show that the particle-accumulated layer is formed in the periphery of the solidified specimen when the diameter of the separated molten metal, the magnetic induction intensity and the separation time are 10 mm, 0.04 T and 1 s, respectively. When the separation time is 2 s, the particle-accumulated layer can be observed obviously and the separation efficiency is about 80%. There are few alumina particles in the inner of the solidified specimen when the separation time is 3 s. The separation efficiency higher than 85% can be achieved when the separation time is longer than 3 s. When the magnetic induction intensity is 0.06 T, the visible particle-accumulated layer can be formed in 1 s and the separation efficiency is higher than 95%. The experimental results were compared with the calculated results at last.

Optimization of the acid leaching process by using an ultrasonic field for metallurgical grade silicon

In the experiment, acid leaching under an ultrasonic field (20 kHz, 80 W) was used to remove Al, Fe, and Ti impurities in metallurgical grade silicon (MG-Si). The effects of the acid leaching process parameters, including the particle size of silicon, the acid type (HCl, HNO3, HF,) and the leaching time on the purification of MG-Si were investigated. The results show that HCl leaching, an initial size of 0.1 mm for the silicon particles, and 8 h of leaching time are the optimum parameters to purify MG-Si. The acid leaching process under an ultrasonic field is more effective than the acid leaching under magnetic stirring, the mechanism of which is preliminarily discussed.

Mathematical model of electromagnetic elimination in tubule with high frequency magnetic field

In order to find the ways to improve the elimination efficiency with high frequency magnetic field, a mathematical model of electromagnetic elimination (EME) in the tubule with high frequency magnetic field was set up. The calculated results show that by ignoring the flow of molten metal, when the surface magnetic induction intensity of the metal (B0) is 0.03 T and the diameter of the tubule is 8 mm, the non-metallic inclusions with 30 μm diameter can be wiped off in 7 s from the center of the molten aluminum, whereas the elimination time of the 5 μm non-metallic inclusions is more than 240 s. When B0 is 0.03 T, the diameter of the tubule is 8 mm and elimination time is more than 30 s, the elimination efficiency of 5μm, 10 μm and 30 μm non-metallic inclusions is about 60%, 90% and 100%, respectively, the elimination efficiency increases with the decreasing diameter of the tubule. It can be concluded that increasing the magnetic induction intensity or decreasing the diameter of the tubule can decrease the elimination time and improve the elimination efficiency in EME with high frequency magnetic field.

Effect of minor B addition on microstructure and properties of AlCoCrFeNi multi-compenent alloy

The influences of slight amount of B element on the microstructure and properties of AlCoCrFeNiBx high entropy alloys (x = 0, 0.01,…, 0.09 and 0.1, mole fraction) were investigated. The AlCoCrFeNi high entropy alloy exhibits equiaxed grain structures with obvious composition segregation. However, with the addition of B element, the alloys exhibit dendrite structures. Inside the dendrites, spinodal decomposition structure can be clearly observed. With the addition of B element, the crystal structures change from (B2 + BCC) to (B2 + BCC + FCC) structures, and the hardness firstly increases from HV 486.7 to HV 502.4, then declines to HV 460.7 (x ≥ 0.02). The compressive fracture strength firstly shows a trend of increasing, and then declining (x ≥ 0.08). The coercive forces and the specific saturation magnetizations of the alloys decrease as B addition contents increase, the decreasing coercive forces show a better soft magnetic behavior.

Grain refinement of pure aluminum by direct current pulsed magnetic field and inoculation

Abstract The combined effects of direct current pulsed magnetic field (DC-PMF) and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% (mass fraction) Al–5Ti–B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μm.

Removal of impurities from metallurgical grade silicon by electron beam melting

Solar cells are currently fabricated from a variety of silicon-based materials. Now the major silicon material for solar cells is the scrap of electronic grade silicon (EG-Si). But in the current market it is difficult to secure a steady supply of this material. Therefore, alternative production processes are needed to increase the feedstock. In this paper, EBM is used to purify silicon. MG-Si particles after leaching with an initial purity of 99.88% in mass as starting materials were used. The final purity of the silicon disk obtained after EBM was above 99.995% in mass. This result demonstrates that EBM can effectively remove impurities from silicon. This paper mainly studies the impurity distribution in the silicon disk after EBM.