Materials Science Forum Vol. 724

Abstract: Recrystallization kinetics of Mg alloy has been investigated in this study. Mg alloys such as Mg-3Al and Mg-6Al in weight percents were cast into rectangular shaped ingots of 20mm thickness. Solution treatment at 400°C for 24 hrs has been carried out on these ingots and pure Mg for comparison. Heat treated ingots including pure Mg were rolled at room temperature by thickness reductions of 10, 20, and 30 percents. Annealing treatment for recrystallization has been conducted on these cold-rolled plates at temperatures of 200, 300, and 400°C for various times from 1 min to 24 hrs. The microstructure observation and hardness measurement conducted on the recrystallized specimens revealed that static recrystallization at 200°C was very slow and expedited with increasing temperature, regardless of Al contents. While recrystallization behavior of Mg at 300°C appeared to be retarded by increase in Al contents, that of Mg was not affected at 400°C.

Abstract: In this paper, it was aimed to develop a new Al-Zn-Mg base aluminum alloy having high electrical conductivity, strength, and formability simultaneously. As a result, Al-Zn-Mg base low aluminum alloy sheet can be effectively strengthened without significant thermal conductivity loss by multiply alloying precipitation hardening elements and properly controlling production process parameters.

Abstract: in this paper, it was aimed to improve understanding about the effects of physical melt treatment on the morphologies of eutectic silicon crystal size, and then the effects of these microstructural features on anodizing characteristics. A380 and A356 casting aluminum alloys were used in this experiment. A twin-screw melt-shearing process and an electro magnetic stirring process were utilized before high pressure die casting. In order to refine and homogenize the microstructure of the diecast Al-Si alloys, the melt-shearing process parameters were controlled and T6 heat treatment was carried out. A uniform microstructure over the whole thickness of the diecast specimens caused smaller difference in oxidation coating layer thickness between machined and non-machined surfaces. More uniform anodic coating layer was obtained by AC/DC coupled anodizing and PEO processes compared to conventional DC anodizing process.

Abstract: The hot deformation behavior of a high strength low alloy (HSLA) steel for construction application under hot working conditions in the temperature range of 900 to 1100 and strain rate range from 0.1 to 10 s^-1 has been studied by performing a series of hot compression tests. The dynamic materials model has been employed for developing the processing maps, which show variation of the efficiency of power dissipation with temperature and strain rate. Also the Kumars model has been used for developing the instability map, which shows variation of the instability for plastic deformation with temperature and strain rate. The efficiency of power dissipation increased with decreasing strain rate and increasing temperature. High efficiency of power dissipation over 20 % was obtained at a finite strain level of 0.3 under the conditions of strain rate lower than 1 s^-1 and temperature higher than 1050. Plastic instability was expected in the regime of temperatures lower than 1000°C and strain rate lower than 0.3 s^-1.

Abstract: 5A06 aluminum alloy welding was obtained by using SAlMg-3 as welding wire with MIG (metal inert gas arc welding). The welded joint with deep cryogenic treatment at liquid nitrogen temperature (-155) for 4h, 8h, 10h were analyzed by metallographic and XRD examination. The results have shown that a lot of subgrain appears in the microstructure of the welded joint resulting in the refined grain after cryogenic treatment. The obvious increasing in content of β-phase (Mg₂Al₃) is distributed and dispersed evenly, contributed to dispersion strengthening of the welded joint. Meanwhile, orientation phenomena is obtained for some grain after deep cryogenic treatment. As a result, the microstructure of the joint can be modified by the deep cryogenic treatment.

Abstract: In this study, Al/Cu composite was produced by hydrostatic extrusion process at 523 K. Mechanical and electrical properties of Al/Cu composite were investigated during isothermal aging. Microstructure observation and composition analysis of the interface was carried out scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. Three kinds of intermetallic composites are observed and they have increased in size as a function of annealing process. Their growth brings about the decrease in the hardness Al/Cu composite.

Abstract: Mg alloy sheets exhibit the yield strength of 280 MPa and elongation of 18 % by rolling at 423 K. Elongation of Mg alloy sheets was improved up to 35 % when the sample was annealed at 673 K for 10 min. From the observation of microstructure, recrystallization and grain growth have happened during annealing processes. The intensity of 0002 pole figure increases slightly as a function of annealing temperature.

Abstract: Generally, there are two ways available for porosity measurement of porous metals. One is by calculating density ratio of a porous metal and a corresponding non-porous metal, called as relative density method. The other is by counting the percentage of pores on cross section of a porous metal, called as image analysis method. In this work, both methods were employed for lotus-type porous copper on porosity measurement. The effects of several parameters in both methods on porosity values of the porous copper are reported and discussed. The relative density method is recommended as porosity by this method is more reliable for the porous copper.

Abstract: Porous Si₃N₄ ceramics were prepared by conventional sintering method with the initial Si₃N₄ powder added different amounts of β-Si₃N₄ seeds and 5 wt.% Y₂O₃. The porosity, density and flexural strength were tested by Archimedes and three-point bending methods, respectively. Microstructure of porous Si₃N₄ ceramics was studied by scanning electron microscopy. The results showed that the fibrous β-Si₃N₄ grains developed in the bimodal porous microstructure and the average aspect ratio of 6.42 by adjusting the β-Si₃N₄ seeds content up to 3 wt.%. Under the porosity of about 42%, the flexural strength of the materials could reached 315.98 MPa.

Abstract: ZnO nanorods were prepared by heat treating of aqueous zinc acetate treated with organic of PVA. The products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The results indicate that the as synthesized ZnO are hexagonal wurtzite nanorods with the maximum aspect ratio of 10:1 (100 nm in diameter and about 1 μm in length). The morphology of nanorods was formed by the regulation of appropriate organic under a pH value of 8.5. The growth mechanism of ZnO is proposed that the nanocrystals grow along a preferred direction in a growth tunnel provided by organics.