Advanced Materials Research Vols. 26-28

Abstract: In order to improve the formability of AZ31 magnesium alloy sheet at room temperature, a new process, so-called equal channel angular rolling (ECAR) and followed by annealing treatment was applied to process the sheet. The optical microstructure of the as-received sheet was similar with that of the ECARed one after annealing treatment, the Erichsen value and limiting drawing ratio of the ECARed sheet was about 6.26mm and 1.6, respectively, which was much larger than that of 4.18mm and 1.2 for the as-received sheet. These can be attributed to the low yield ratio and high strain hardening exponent due to the modified texture induced by the shear deformation during ECAR process, which is favor of the activations of basal slipping and twinning at ambient temperature, especially deforming at the rolling direction.

Abstract: In order to clarify the effect of alloying elements on the axial ratio of magnesium binary solid solutions, the solid solutions of Mg-Al, Mg-Zn, and Mg-Li with various concentrations were casted and homogenized. Synchrotron X-ray diffraction patterns were then obtained from annealed powder samples and analyzed using the Rietveld method. The effects of solutes concentration on lattice parameters were explained on the basis of atomic size difference and valence electron effect, which changes electron overlap of magnesium. It has been found in this study that Al and Li raise and reduce the c/a ratio, respectively, while Zn has no effect on the c/a ratio.

Abstract: Aluminium alloys have been widely used in the structure of aircraft and passenger car because of its lightweight. It is also interested in the lightweight products to improve the fuel efficiency. In this research, forging design of Al rotating arm holder has been studied by FE analysis. Structural analysis of the model was performed at first. From the results of the analysis, effective stress, effective strain and safety factor acting on the component were obtained.

Abstract: The effects of different solid solution and aging technologies on the microstructure of AM50 were studied. The results indicated that heat-resistant Al-Mn phases were the major second phases in AM50 alloy under all testing conditions. Highest microhardnesses were obtained not only in as-aged sample but in as-solution treated sample, which indicated that the strengthening mechanism for AM50 alloy was not limited to precipitation reinforcement.

Abstract: Compressive torsion combined loading that uses relatively low compressive pressure has a great advantage of microstructure refinement of cylindrical metal blocks without changing their shape while processing. In the present work, effects of processing temperature and rotation times on homogeneity of the refined microstructure were investigated for Al-5%Mg alloy. Although lower processing temperature was effective to obtain fine grains, it was difficult to obtain homogeneous refinement at lower temperature. Higher processing temperature was favorable to obtain homogeneous microstructure, for instance, in the cylindrical specimen of φ25×10 mm the homogeneous refinement could be obtained at higher temperatures than 373K. Increasing rotation times was also effective to obtain homogeneous refined microstructure for thicker specimens.

Abstract: A quantitative study of the interactions between microstructural features such as secondary dendrite arm spacing (DAS), eutectic structure and fatigue behavior of two Al-Si-Mg casting alloys with silicon contents of 7% and 10% respectively, has been conducted. In the condition of minimizing casting defects, the influence of microstructural features on the mechanical performance becomes more pronounced. Depending on the magnesium content affecting the strength of the matrix, the tensile properties were changed upon experimental conditions; the tensile strength was increased with magnesium content, whereas the elongation was increased in the reverse case. The increase of both of high cycle fatigue and low cycle fatigue lives with decreasing the secondary dendritic arm spacing is observed, mainly due to homogeneous deformation owing to the fine size of eutectic silicon and Fe intermetallic particles. The fatigue dynamometer of a diesel cylinder head shows the same tendency with the results of specimen fatigue tests with microstructures.

Abstract: The addition of strontium to Mg-Al based alloys offers good creep resistance to meet the material requirements for automotive applications. The composition, microstructure and mechanical properties of Mg-Al-Sr alloys are discussed in this paper. The effects of alloy elements such as Ca, Ti and Mn in Mg-Al-Sr alloy are summarized. Technologies for preparation of Mg-Sr master alloy were developed, including mixture method and vacuum thermal reduction method which may also be used for preparation of Mg-Al-Sr alloys.

Abstract: Suspended on Mg-base melt, SrCl2 was electrochemical reduced to prepare Mg-Sr alloy. The kinds of Sr-compounds, composition ratio of flux, temperature of molten salt and Mg-base molten bath and recovery of Sr were discussed. According to theories and experiments, this paper presents the relations between the adding flux and reduction of Sr-compounds with the technical parameters. The electrode reactions and the Gibbs Free Energies were evaluated based on thermodynamics analysis. The results show that composition of flux played important roles in the reduction process. The optimized technical flow and parameters for the application of the new method were advised.

Abstract: Heat-treatable 6000-series alloys are currently used by automotive body sheets. It is general to improve mechanical properties of the Al-Mg-Si alloy by giving addition of the element and the thermo-mechanical treatment. The electron backscattered pattern (EBSP) technique has been performed in order to analyse individual crystallographic orientation in these alloys. Hardness of the 30%-rolled alloy was higher than that of the 0%-rolled alloy. The Schmid factor of individual crystal grain was calculated by crystallographic orientation. After adding a little deformation, the crack was observed at the interface between higher SF and lower SF grains. It was thought that this crack introduced a fracture from the surface.

Abstract: It is very popular to improve mechanical properties of Al-Mg-Si alloys by adding other element. For example, it is well known that addition of transition metals is useful because the refinement of grain size can be achieved, and with the addition of Cu to Al-Mg-Si alloy can increase the strength and hardness of the materials. Also, there are a few reports about the addition of Ag, which is particularly good for elongation. However, even now it has not been clarified yet why Cu and Ag are useful in improving alloys elongation. In this work, we have investigated the tensile behavior of excess Si-type Al-Mg-Si alloys, which contain Cu. The tensile test and hardness measurement were carried out. Scanning electron microscope (SEM) was used to investigate the fracture surfaces and individual crystallographic orientation. After small additional deformation, the crack was observed by the interface between higher Schmid Factor (S.F.) and lower S.F. grains. It was thought that this crack influenced fracture from fracture surface.