The Influence of Initial Purity Level on the Refining Efficiency of Aluminum via Zone Refining

Zone refining is a well-known technique, usually using pure initial materials to produce high purity metals. However, the effectiveness of zone refining in the purification of different purity levels of metals as well as its feasibility for use as a recycling technique for low quality metals are rarely investigated. In this work, conducted at IME/RWTH Aachen University, three kinds of Al with different purities, i.e., three-layer electrolysis (4N), commercial pure (2N8) and recycled Al (1N7), were put on focus to address the above-mentioned issue. The experiments were conducted with an optimized zone length combination at the moving rate of 1.2 mm/min for five zone passes. The results showed that the 4N pure initial Al was improved to 5N5 after five passes, much higher than the results for commercial pure- or recycled Al, where less than 50% reduction of total impurities was achieved.

Physical Simulation on Molten Steel Flow Characteristics of RH Vacuum Chamber with Arched Snorkels

The RH vacuum refining technology is a vitally powerful method of producing clean steel. The inner diameter of traditional circular snorkel is very difficult to be increased owing to the metallurgical refractory thickness around the snorkels and the limitation of the area under the vacuum chamber, limiting the increase in refining efficiency. In order to improve the refining efficiency of the RH reactor, a new designed RH degasser with an optimized arched snorkel is established. This design replaces the traditional two circular snorkels structure with the two arched snorkels and greatly enhances the cross-sectional area of snorkel. In this study, the flow characteristics of this new type RH were studied and analyzed by establishing a 1 : 5.5 physical model of RH with arched snorkels. Results show that the circulation flow rate of RH with arched snorkels can increase by 100% ∼ 180% and the mixing time approximately decreases by 35% compared with RH with circular snorkels under actual production conditions. The circulation flow rate of RH with arched snorkels continues to increase obviously when gas flow rate exceeds the saturated value of RH with circular snorkels. The RH with arched snorkels can increase the refining efficiency significantly and has important application prospect.

Enhancement of microstructure uniformity and grain refining efficiency of Al-5Ti-1B alloy via powder extrusion

Microstructure uniformity and grain refining efficiency of Al-5Ti-1B alloy rod prepared by powder extruded process and continuous casting and rolling process are investigated in detail by X ray diffractometer, scanning electron microscope and electron probe. It is found that TiB2 and TiAl3 particles are uniformly distributed in the powder extruded Al-5Ti-1B alloy via gas atomization and hot extrusion process. The samples with 0.2% powder extruded Al-5Ti-1B alloy rod holding for 2 min consist of equiaxed grains with an average diameter of 183 µm. Even the holding time extended to 180 min, the average diameter is still stable (229 µm). Al-5Ti-1B alloy rod prepared by the powder extruded process presents better grain refinement and stronger resistance to grain coarsening.

Revealing the Nuclei Formation in Carbon-Inoculated Mg-3%Al Alloys Containing Trace Fe

In this study, Fe-bearing Mg-3%Al alloys were inoculated by combining carbon with or without Ca. Both processes can significantly refine the grain size of Mg-3%Al alloys. The highest refining efficiency can be obtained by carbon combined with Ca. The synergistic grain refining efficiency can be attributed to the constitutional undercooling produced by the addition of Ca. Two kinds of carbon-containing nuclei with duplex-phase particles and cluster particles were observed in the carbon-inoculated alloys. A thermodynamic model was established to disclose the formation mechanisms of the duplex-phase particles and Al4C3 cluster particles. This thermodynamic model is based on the change of Gibbs free energy for the formation of these two kinds of particles. The calculated results show that these two particles can form spontaneously, since the change of Gibbs free energy is negative. However, the Gibbs free change of the duplex-phase particle is more negative than the Al4C3 cluster particle. This indicates that the adsorption process is more spontaneous than the cluster process, and tiny Al4C3 particles are preferred to form duplex-phase particle, rather than gathering to form an Al4C3 cluster particle. In addition, the addition of Ca can reduce the interfacial energy between the Al4C3 phase and the Al–Fe phase and promote the formation of duplex-phase particles.

Characterization of the Mixing Flow Structure of Molten Steel in a Single Snorkel Vacuum Refining Furnace

With the demand of high-quality steel and miniaturization of the special steel production, single snorkel vacuum refining process has been widely concerned in China recently, because of its simple structure and good performance of degassing and decarburization. In this study, a water model experimental system and a three-dimensional mathematical model based on two-fluid multiphase flow model have been built to analyze the refining efficiency limitation of the single snorkel vacuum refining furnace from the flow pattern and gas distribution. The results showed that there is a limited gas flow rate, and beyond this flow rate the gas column deviates to the wall and the redundant bubbles escape from the free surface, which will not further improve the refining efficiency and will lead to the erosion of the snorkel. In this case, the limited flow rate is 900 NL/h. Furthermore, the fluctuation of the free surface and the different structural parameters have significant effects on the flow field in single-snorkel vacuum refining furnace (SSF).