Advanced Materials Research Vols. 26-28

Abstract: Manufacturing processes of Ti-6Al-4V plane and profiled ring-products were investigated with three-dimensional FEM simulation and experimental analyses. FEM simulation for the ring-rolling process was used to calculate the state variables such as strain, strain rate and temperature. To induce the uniform deformation of the profile ring and reduce the applied load, the final blank was prepared by two-step processes. The mechanical properties of Ti-6Al-4V alloy ring products made in this work were investigated with tensile and impact tests, and compared with the specification(AMS-T-81915).

Abstract: Dynamic recrystallization behavior of Mg-3.1wt.%Al-0.1wt.%Y alloy was investigated. During extrusion, dynamic recrystallization occurred and very fine microstructure was obtained. We compared the relationship between Zener-Hollomon parameter, Z, and the dynamically recrystallized grain size, drec, and between the normalized recrystallized grain size, drec/d0, where d0 is the initial grain size, and Z for Mg-3.1wt. %Al-0.1wt.%Y with commercial Mg-3Al-0.5Zn alloy. As the result, the dynamically recrystallized grain size of Mg-3Al-0.1Y was finer than that of Mg-3Al-0.5Zn alloy under the equivalent Z, while the initial grain size of Mg-3Al-0.1Y was coarser than Mg-3Al-0.5Zn alloy. The normalized grain size for Mg-3Al-0.1Y alloy was much smaller than that of Mg-3Al-0.5Zn alloy under the equivalent Z. We conclude that small addition of Y to Mg-Al alloys is effective for grain refinement by dynamic recrystallization.

Abstract: Industrial application of magnesium alloys has increased significantly recently. However, wrought magnesium alloys still have a lot of technical challenges to be solved for more applications. First of all, low formability of wrought alloys should be improved by optimizing the processing variables. In the present study, the effect of process variables such as forging temperature and forging speed were investigated to forgeability of magnesium alloy. To understand the effect of process variables more specifically, both numerical and experimental works have been carried out on the model which contains upsetting geometry. Forgeability of AZ31 alloy was found to depend more on the forging speed rather than temperature. Forged sample showed a significant activity of twinning, which was found to be closely related with flow uniformity.

Abstract: Silicon nitride was prepared by means of low-pressure preheating combustion synthesis in this paper. When N2 pressure is less than or equal to 2MPa, the lowest preheating temperature is about 653K, reactant could make silicon nitride by combustion synthesis. The additive of ammonium fluoride and ammonium chloride, as the reactive diluent, and Si react and make some useful intermediate products to α -Si3N4 after thermal decomposition. The reactive diluent content must be appropriate. At the same time, with the improvement of Si3N4, as the inert diluent, content in reactant, the adiabatic flame temperature of system would reduce, and combustion reaction rate of Si also drops, so it is propitious to make high level of α -Si3N4.

Abstract: Powder Metallurgy (P/M) is mainly composed of four steps: powder feeding, compaction, ejection, and sintering. A feedshoe moves forward and backward over the die cavity to fill it with metal powders. Possible problem in this stage is the uneven supply of powder on the horizontal direction. It can cause tool breakage due to uneven density distribution. Unevenly-distributed powder also causes internal cracks during compaction or warpage during sintering. Another problem during powder feeding is the inclusion of air with powder. This changes the overall density of the part. Powder feeding mechanism is very important, because it is the first step in the process. If there is imperfection during powder feeding, the final part ends up with a bad part no matter how perfect the rest of the processes are. This paper describes the development of an advanced powder feeding mechanism, which allows well-distributed amount of powder to be delivered to the die cavity.

Abstract: Dynamic recrystallization behavior that occurs during the hot extrusion was examined in two commercial Mg alloys, AZ31 and AZ80 alloys. The initial grain size, d0, and the dynamically recrystallized grain size, drec, after the extrusion was investigated using optical microscopy. The dynamically recrystallized grain size decreased with an increasing the Zener-Hollomon parameter.

Abstract: In this study, an automated scrap-sorting system using image processing technology has been designed and examined to automatically sort out specified materials from a mixture, especially Cu and other non-ferrous metal scraps from a mixture of iron scraps. In the functional tests of the system, its efficiency in the separation of Cu scraps from its mixture with Fe ones reaches to 75 % or more at a conveying speed of 20 m/min., and thus it is expected that the system can be commercialized in the industry of shredder makers if an automated sorting system of high speed is realized.

Abstract: The possibility for preparation of biodegradable film from cellulose-enrich waste was studied. This work dealt with the synthesis of cellulose film in LiCl/DMAc solvent system by microwave-induced esterification of cellulose from waste cotton fabric using DMAP and lauroyl chloride as a catalyst and esterifying agent, respectively. The cellulose laurate film was prepared by casting method. The structure of cellulose laurate was confirmed by FTIR and 1H-NMR analyses. The thermal stability was characterized by TGA. The optimum condition for esterification in terms of microwave power and time was investigated. The films obtained were tested for their tensile properties and potentiality of biodegradation.

Abstract: The influence of annealing atmosphere on mechanical and wear properties of free-cutting phosphor bronze alloy was investigated. After annealing in vacuum, the mechanical properties of the alloy decreases due to vaporization of alloying element. In addition, the softening of matrix induces decreasing the wear resistance dramatically. In contrast, high mechanical properties were observed in the alloy annealed in air and in nitrogen atmosphere. In particular, a large smearing of lead in the alloy annealed in air atmosphere was observed and was affected on the enhancement of wear resistance. Consequently, annealing in vacuum atmosphere is not suitable for high mechanical properties and wear resistance.