Materials Science Forum Vol. 850

Abstract: Ruthenium is widely used as catalyst, magnetic recording and electrode materials. In this study, high-purity (≥99.995 wt%) ruthenium sponge was synthesized from crude ruthenium (≤99.9 wt%) by chemical refining technique. Initially, crude Ru was transformed into H₂RuCl₆ by distilling treatment. The H₂RuCl₆ was, then, added with NH4Cl powder to precipitate (NH₄)₂RuCl₆ powder. Afterward, the (NH₄)₂RuCl₆ powder was ignited in air and transformed into RuO₂. Finally, RuO₂ was changed to Ru by hydrogen reduction method. Impurities included in the starting Ru powder were eliminated after distillation and precipitation treatments. As-obtained ruthenium particles were spherical-like agglomeration, the average size was about 6 μm and the powder density was 11.83 g/cm³. The details of chemical transforming mechanisms in the refining process were described.

Abstract: Setup calculation function of the process control system for tandem cold rolling mills not only determinates the dimension accuracy of finished strip materials directly, but also affects the control of surface quality of strip materials. In the present work, an attempt was made to develop a new setup calculation method for tandem cold rolling mills to maximize the throughput and improve the surface quality of strips. Based on the application platform for level-2 process control system, the modular design method was adopted, and then the setup calculation function was developed. And four functional modules consisting of preset preparation module (PPM), basic setup calculation module (BSCM), dynamic setup calculation module (DSCM), and adaptive calculation module (ACM) were developed. The preset data from PPM were used in equipment of level-1 process control system, and the purposes of BSCM was to achieve high quality of products, reduce off thickness deviation and achieve stable rolling at maximum possible rolling speed for raising productivity. In order to minimize off error of preset and actual data, DSCM was provided. Thanks to the design of ACM, accuracy of mathematical model can be effectively improved on line. Ultimately, the precise model on setup calculation method for cold tandem rolling of strip steels was established, and then it was put into practical production. Statistics analysis showed that the measured data was in excellent agreement with the model, and exactly, the relative deviations on rolling force and delivery thickness of strips were less than 3.67% and 0.42%, respectively. The new setup calculation method has high precision and good generalization capability.

Abstract: The effect of local pressurization on mechanical properties and fracture behavior of indirect squeeze-cast A354 alloy has been investigated. As compared to conventional process, the porosity and shrinkage cavity for heavy sectioned squeeze castings were improved by the indirect squeeze casting, while its tensile properties were inferior to other parts of the casting. That is mainly due to that inhomogeneous eutectic Si particles within strip, angular and fragment shapes distribute in bulky α-Al cells, which is caused by slower solidification rate. After T6 treatment, the fragmentation and spheroidization of the eutectic silicon happened. Under this situation, the effect of fragmentation on α-Al matrix reduced. Tensile properties of the casting (both local pressurization part and non-local pressurization part) were enhanced greatly, by 36.8% and 25.4%, respectively. Fracture analysis results show that the type of fracture morphology is changed from mixed mode of brittle cleavage and ductile to ductile mode after T6-treatment.

Abstract: The effects of Mg and Cu additions with different contents on the mechanical properties of Al-Si alloy prepared by indirect squeeze casting have been experimentally investigated. The microstructure and mechanical properties of as-cast and T6-treated Al-Si-Cu-Mg alloys were tested by OM, SEM, DSC and tensile measurement, where the samples were produced by artificial aging at 180°C for 8 h after solution treatment at 540°C for 4 h. It has been found that for the as-cast alloys, with increasing contents of Mg and Cu the tensile strength (UTS) and yield strength (YS) increased, while the percentage elongation (El) decreased. And the optimal mechanical properties of Al-Si-Cu-Mg alloys were obtained under the content ratio of Cu/Mg within 4, where the UTS and El reached 426 MPa and 6.3% after T6 treated, respectively.

Abstract: Plasma-MIG hybrid welding and MIG welding of 5083 marine aluminum alloy was carried out. The influences of parameters of welding process on the weldments morphology were investigated in order to optimize the welding process parameters. The macrostructure, microstructure, tensile and bending properties of the optimized joint were studied. The results show that Plasma-MIG hybrid welding not only has a synergistic effect of Plasma and MIG welding but also has a high welding efficiency. Welding speed, Plasma current and MIG current have a significant effect on welding penetration and welding morphology. Meanwhile, the ductility and strength property of weld joint was qualified though the bending test and tensile test. The average tensile strength of weld joint is about 285MPa at room temperature, about 86% of the base metal.

Abstract: The influences of spinning deformation and heat treatment on microstructure and tensile properties of A356 alloy at different cooling rates were investigated in this study by optical and scanning electron microscopes. The results indicated that spinning deformation enhanced the tensile properties of the alloy due to the reduction of Si size and porosity percentage, especially in the samples with coarse microstructure. Heat treatment increased the strength while decreased the ductility of the alloy because of the precipitation of brittle Mg₂Si in Al matrix. It is suggested that the spinning deformation processing is an effective technique to produce A356 alloy wheels with high mechanical properties.

Abstract: The effects of two-step aging on the microstructure and mechanical properties of Cu-2.7Be alloys were investigated in the present study, compared with one-step aging. After cold rolling the Cu-2.7Be alloys were heated by different combinations of temperature and time. The results revealed that two-step aging could obviously increase the strength of Cu-Be sheets when the aging temperature was 380 °C. At the temperature of 320 °C and 340 °C, there was no distinctly difference of strength and elongation between two-step aging and one-step aging. The SEM of fracture surfaces showed that the number of dimples increased with the increase of aging temperature.

Abstract: Many factors can influence the density uniformity of the SiC particle reinforced aluminum matrix composites, including the material preparation method and the material processing technology. The influence factors on the density uniformity of SiC_p/2024Al in the extrusion process were studied in the present investigation. Those factors contain the extrusion ratio, the extrusion velocity, the temperature and the friction coefficient. The flow stress of this material under different temperatures and strain velocities was tested by heat physical simulation experiments. As a result, the true stress-strain curve was obtained and the phenomenological constitutive equation was established, and the FEM simulation was used for the extrusion process. The velocity gradient computed by the numerical simulation was used to describe the density uniformity. The density uniformity caused by different extrusion process parameters was compared and analyzed. The results showed that the density uniformity was improved obviously by the optimization of extrusion process parameters. At last, the real extrusion process test was organized to verify the numerical simulation results and the most suitable characteristic parameters of the extrusion mold and the process was finally determined.

Abstract: In order to develop high-performance lead-free brasses, the effect of magnesium content on the machinability of lead-free brass alloys was carefully studied in the present work. The ingots of the Cu-Zn-Bi-Sb alloy were fabricated in terms of different magnesium contents of 1.0, 2.0, 3.0 and 4.0 wt%. The difference in the machinability of the Cu-Zn-Bi-Sb alloy ingots was discussed in terms of their microstructure, mechanical properties and chip morphologies. X-ray diffraction analysis indicated that α phase (0~38 Zn by atom %), β phase (45~49 Zn by atom %), CuMgSb and CuMgZn existed in the Cu-Zn-Bi-Sb alloys with the different magnesium contents. With increasing the content of magnesium, the machinability of the present lead-free brass alloys was markedly improved, which is mainly attributed to the formation of intermetallic compounds such as CuMgSb and CuMgZn.

Abstract: A Fe-3wt% Si strip was produced using a vertical type twin-roll casting process. Sub-grains with an inhomogeneous distribution through the thickness direction were firstly observed in the as-cast strip. It was found that the surface layer was characterized by columnar grains containing lineage sub-grains, the subsurface layer was dominated by numerous polygonal sub-grains inside columnar grains or fine equiaxed grains, and the center layer was composed of coarse equiaxed grains without sub-grains. In addition, the sub-grain boundaries provided additional nucleation sites for precipitates and the nanoscale MnS particles were successfully obtained. Moreover, the average size of MnS precipitates in the surface layer was smaller than that in the subsurface layer. The inhomogeneous distributions of sub-grains and precipitates can be attributed to the large temperature gradient through the thickness direction during the strip casting process.