Advanced Materials Research Vols. 284-286

Abstract: Effects of anisotropy on the microstructural characteristics and mechanical behavior of shock loaded of AZ31 magnesium alloy have been investigated. Using electron backscatter diffraction, tension twinning was observed in both shock loading directions along the normal (ND) and rolling directions (RD). Compression tests were carried out along ND and RD in both as-received and post-shock conditions. It indicated that the RD samples show a more notable hardening behavior compared to the as-received conditions. Moreover, it is postulated here that detwinning results in a drop of strain-hardening rate for the ND samples under post shock reload conditions and tension twinning formed during the shock wave loading process leads to a significant moving left of the peak strain hardening rate for the RD samples under post shock reload conditions.

Abstract: A Split Hopkinson Pressure Bar system was employed to investigate the compressive dynamic mechanical behaviors of Ti-10V-2Fe-3Al (Ti-1023) alloy with lamellar microstructure, over a broad strain rates ranging from 1500/s to 5100/s. The results reveal that the strain rate has a significant effect on the flow stress of Ti-1023 alloy, and there exists serious thermal softening as the strain rate exceeds 3200/s. The critical strain rate of fracture for this alloy is 2300/s. The microstructure examination indicated that adiabatic shear bands (ASBs) bifurcate more intensely with the increasing of strain rate. Micro-voids nucleate either in the ASB or interface between shear band and matrix bulk. Finally, fracture of this alloy proceeds through the nucleation, growth and coalescence of these voids and cracks along the ASBs.

Abstract: The oxidation of binary Co-10Cr alloys in 1 atm of pure O₂ at 700 and 800°C was investigated. It indicated that the oxidation followed approximately the parabolic rate law (n=2). The parabolic rate constants as functions of temperature were 2.03×10^-11, 7.05×10^-10 g²cm^-4s^-1, respectively. The scales formed on Co-10Cr alloys were double-layered. The outer layer composed of large columnar CoO grains was relatively compact, while the inner CoO layer was porous, fine-grained and doped by cobaltous oxide CoO and spinel CoCr₂O₄.

Abstract: The soft-magnetic properties and service life of amorphous or nanocrystalline Fe_73.5Si_13.5B₉Nb₃Cu₁ have been influenced by the corrosion of the alloy. In this study, the electrochemical corrosions of amorphous Fe_73.5Si_13.5B₉Nb₃Cu₁ in the blend solutions of sodium chloride and sodium hydroxide were investigated by linear polarization (PLZ) and electrochemical impedance spectroscopy (EIS) technique. The presence of OH^- in the blend solution gave rise to typical passivation of the alloy. A suitable concentration of OH^- was required for the low corrosion rate. And the higher concentration of OH^- led to a faster corrosion. Increase of concentration of Cl^- aroused more obvious corrosion. These results were ascribed to the deteriorating effect of Cl^- and high-concentration OH^- on the passive film formed on the surface of amorphous Fe_73.5Si_13.5B₉Nb₃Cu₁.

Abstract: In this paper, the effect of Er element on ignition-proof property of Mg-Zn alloys was studied. XRD, SEM and EDS were used to investigate the ignition-proof performance and the oxidation film of the alloys. The element of Er tended to enrich in the surface of molten magnesium alloys during the oxidation process. And the oxidation film was composed of MgO and Er₂O₃. With the Er content in Mg-Zn alloy increasing, the content of Er₂O₃ in oxidation film increases and the ignition point of Mg-Zn alloys rise. So Er can improve the ignition-proof properties of Mg-Zn alloys greatly.

Abstract: Mg-5Al-0.3Mn-1Ce alloy was prepared by metal mould casting method. The as-cast ingot was homogenized and hot-rolled with total thickness reduction of 61% after four passes. Texture, microstructure and mechanical properties of the studied alloy were investigated. Results showed that the as-cast sample was mainly composed of a-Mg, Mg₁₇Al₁₂ and Al₁₁Ce₃ phases. Average grain size of the as-cast sample was about 500 μm. After hot-rolling, average grain size was greatly refined to about 20 μm. Further more, the long acicular Al₁₁Ce₃ phase was smashed to small pieces. Tensile test results demonstrated that ultimate tensile strength and yield strength of the hot-rolled sample were improved by 65.2% and 165% respectively compared with those of the as-cast sample. Strength enhancement was attributed to grain refining strengthening and dislocation strengthening mechanisms.

Abstract: The microstructure and creep property of as-cast Mg-6Al-xSr(x=0, 2,3) alloys were studied. Results showed that the branch-like Al₄Sr phase is the main precipitating phase in these alloys containing Sr. Their secondary creep rates under the applied stress of 70MPa at 175°Cdecreased with the increasing in the content of Sr and reached the minimum value of 1.4×10^-8s^-1 in the Mg-6Al-3Sr alloy, which is one thirtieth of secondary creep rates of the Mg-6Al alloy. It was mainly attributed to Al₄Sr, which effectively hindered the grain boundaries sliding and dislocation motion in the creep.

Abstract: Mg-4.9Zn-0.9Y-0.7Zr alloy and Mg-4.9Zn-0.7Zr used as compared alloy were prepared by ingot metallurgy method. The influence of Y addition on microstructure and properties was studied. Phase analysis, microstructure and morphology of second phases were investigated by XRD, OM and SEM. The component and morphology of the second phases was analyzed by EDAX and TEM. The results showed that, Y was an effective element strengthening Mg-Zn-Zr alloy, a large number of Mg₃Zn₆Y phase was formed due to the addition of Y. During the process of hot rolling, Mg₃Zn₆Y phase was pulverized into large amount of dispersion particles, which pinned dislocation effectively, so ultimate strength and yield strength at room temperature were improved, as well as good plasticity was remained.

Abstract: Micro-structure nickels were fabricated by LIGA, and their surface morphology, microstructure and texture were studied by Microscope, SEM and XRD. The results show that the specimens have uneven microstructure, and the grains are relatively small. The grains grow mainly by the form of columnar and cluster-like, and there are obviously preferred orientation in the (220) plane.

Abstract: The dynamic deformation behavior of an as-extruded Mg-Gd-Y magnesium alloy was studied by using Split Hopkinson Pressure Bar (SHPB) apparatus under high strain rates of 102 s-1 to 103s-1 in the present work, in the mean while the microstructure evolution after deformation were inspected by OM and SEM. The results demonstrated that the material is not sensitive to the strain rate and with increasing the strain rate the yield stress of as-extruded Mg-Gd-Y magnesium alloy has a tendency of increasing. The microstructure observation results shown that several deformation localization areas with the width of 10mm formed in the strain rates of 465s-1 and 2140s-1 along the compression axis respectively, and the grain boundaries within the deformation localization area are parallel with each other and are perpendicular to the compression axis. While increasing the strain rate to 3767s-1 the deformation seems become uniform and all the grains are compressed flat in somewhat. The deformation mechanism of as-extruded Mg-Gd-Y magnesium alloy under high strain rate at room temperature was also discussed.