Advanced Materials Research Vols. 299-300

Abstract: The melt of nonleaded free-cutting brass is modified by the electric pulse and the effects on the solidification structure and properties of Silicon Brass are studied with different Bi contents and under different pulse parameters. The results show that the varieties of Bi contents and pulse parameters have a greater impact on grain size and microstructure uniformity of the brass. After silicon brass with 0.5% Bi is modified by electric pulse, the Bi grain size is reduced to 5μm from 30μm, and its shape is changed into being granular from worm-like or long-strip-like, distributed more evenly in α phase and α phase boundary, and a few of which goes into the β phase matrix.

Abstract: Molecular dynamics with an embedded atom method was used to study the coalescence of heteroclusters at different temperatures. The coalescences between heteroclusters and homoclusters were compared. The results showed that: the coalesced complex of two liquid heteroclusters separated into two small droplets at or above a certain temperature which was much higher than the melting temperature of each cluster. When the temperature was lower than the value, the ordered alignment on the close packed (111) facet was induced by Ni cluster. These phenomena did not occur during the homoclusters coalescence.

Abstract: It was investigated that the effect of electric pulse modification (EPM) on the hot tearing of Al-5%Cu-0.8%Mn alloy. The results indicate that hot tearing tendency of all samples can be reduced treated by electric pulse with different parameters, moreover, hot tearing stress of alloy with EPM was enhanced 3 times or so than that of samples without treatment. Decreasing the quantity of eutectic in grain boundaries, decreasing the end-solidifying temperature of the alloys, and refining the grains are main causations for increasing hot tearing resistance of Al-5%Cu-0.8%Mn alloy by electric pulse modification.

Abstract: Study on the instantaneous n-value of 0.3C-1.5Mn-1.5Si steel subjected to 1-step quenching and partitioning process (Q&P) is presented. The result indicated that the curves of instantaneous n-value vs. true strain could be divided into three stages. First, the instantaneous n-value shows a rapid decrease, then a comparative stable stage was observed due to the TRIP phenomenon of retained austenite, at last the instantaneous n-value decreases sharply to zero when necking appearance. The relationship of instantaneous n-value and partitioning temperature (PT) was analyzed; n-value decreased along with the rise of PT due to a higher carbon concentration and lower volume fraction of retained austenite was obtained at higher PT which could influence the uniform elongation and the stability of retained austenite.

Abstract: It was investigated that the effect of electric pulse modification (EPM) on the hot tearing of Al-5%Cu-0.8%Mn alloy. The results indicate that hot tearing tendency of all samples can be reduced treated by electric pulse with different parameters, moreover, hot tearing stress of alloy with EPM was enhanced 3 times or so than that of samples without treatment. Decreasing the quantity of eutectic in grain boundaries, decreasing the end-solidifying temperature of the alloys, and refining the grains are main causations for increasing hot tearing resistance of Al-5%Cu-0.8%Mn alloy by electric pulse modification.

Abstract: The mean stress caused by a non-symmetrical load significantly influences the fatigue limit. The fatigue limit of an aluminum alloy-welded joint is analyzed in the present paper using a stress ratio of 0.3. Our results show that the aluminum alloy-welded joint fatigue limit amplitude can be accurately converted from the mean stress using the Goodman beeline and Eurocode9 methods.

Abstract: The structural and electronic properties of bulk and (001) surface of TiAl₃ have been examined by the first-principles total-energy pseudopotential method based on density functional theory. The lattice constants and heat of formation of bulk TiAl₃ we obtained are in good agreement with the experimental and other theoretical values. The calculated bulk properties indicates that bonding nature in TiAl₃ is a combination of metallic and ionic, in which the metallic bonding become the predominate one. the strongest hybridization exist in the DO₂₂ structure, the Al-3p and Ti-3d bonding of TiAl₃ play the dominant role in hybridization. The structural relaxation and surface energy for (001) slab have been simulated to make sure the stability of slabs with different atomic layers. Compared to TiB₂ (0001) slab, TiAl₃ surfaces shows smaller structural relaxation and lower surface energy, furthermore, the charge redistribution of (001) slab shows almost the same characteristics as bulk TiAl₃, which confirms structural stability of TiAl₃ with (001) slab. This present work makes a beneficial attempt at exploring TiAl₃ surface as an ab initio method for studying possible nucleation mechanism of Aluminum on it.

Abstract: Study the properties of GFRP confining concrete column through eight groups columns subjected to axial loading, and receive the stress-strain curves; various design parameters, such as amounts of GFRP sheets, width of straps and spacing of straps, have been considered. The results are: The axial compressive strength and ductility of concrete prism wrapped by GFRP sheets or GFRP straps have all increased to a certain degree, the process of destruction of concrete prism wrapped by GFRP become slower than common concrete prism. Based on the test results, deducing and validating the stress-strain relationship model of GFRP confining concrete prism.

Abstract: The corrosion behavior of Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy in 3.5% NaCl solution was investigated by using potentiodynamic polarization experiments and electrochemical impedance spectroscopy (EIS). The results show that Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy has the better corrosion resistance than its corresponding crystal alloy. During the bath in the 3.5% NaCl solution at 25°C, Zr53.5Cu26.5Ni5Al12Ag3 alloy has the lower corrosion current density than the corresponding crystal alloy. After 100h, the corrosion current densities of Zr53.5Cu26.5Ni5Al12Ag3 and the corresponding crystal alloy are 3.8415×10-8A/cm2 and 5.2827×10-7A/cm2, respectively. The results of EIS test indicate that Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy has the excellent corrosion resistance because passive film with stable structure formed on the surface in 3.5% NaCl solution. With an increase in the immersion time, the passive film becomes thicker. It leads to impedance resistance and corrosion resistance decrease. The surface of Zr53.5Cu26.5Ni5Al12Ag3 bulk amorphous alloy in 3.5% NaCl solution for 100h was analyzed by SEM and EDS. The results show that the corrosive pitting can be found at both the amorphous alloy and the corresponding crystal alloy. However, the amorphous alloy has the better corrosive pitting resistance than the crystal one because the corrosion products formed by selective dissolving of Zr and Al elements. Moreover, the addition of Ag element helps to improve the corrosion resistance of the amorphous alloy greatly.

Abstract: A warm pre-tension rotation bending process is presented to bend the AZ31 profile. A 3D elastic-plastic thermo-mechanical coupled finite element model is established to investigate the effect of forming temperature on the geometric accuracy of the profile. The results indicate that with increasing forming temperature, the springback angles decrease from 8.37° to 7.2°; the bending radii decrease from 90.69 mm to 89.67 mm; the cross-section distortion of the bent profile increases.