THERMEC 2006 Supplement

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Authors: Sofiene Amira, M. Shehata, Dominique Dubé, R. Tremblay, Edward Ghali
Abstract: The corrosion behavior of AXJ530 magnesium alloy in 3.5% NaCl solution at 25°C and pH 7.25 has been studied. Die-cast and thixocast specimens were tested using constant immersion technique, potentiodynamic polarization measurements and electrochemical noise analysis. The microstructure of cast specimens and their surface aspect after corrosion tests were analysed and compared. The results show that thixocast specimens have the best corrosion resistance. Their superior corrosion resistance can be attributed mainly to the presence of large pre-existing α-Mg grains.
Authors: J.P. Weiler, J.T. Wood, R.J. Klassen, Éric Maire, R. Berkmortel, G. Wang
Abstract: A series of AM60B, die-cast magnesium alloy specimens have been examined using xray tomography at spatial resolutions from 1 – 20μm and further characterized in uniaxial tension. This paper first reports the utility of a critical strain model to link the local area fraction of porosity and the fracture strain. A discussion of the trade-off between predictive accuracy and the spatial resolution of the imaging technique is also presented in order to address the technological implications of these results. In the second half of the paper, serial tomographic imaging is used to illustrate the evolution of damage with increasing uniaxial strain. The implications are discussed with respect to numerical modeling of the performance of die-cast magnesium components.
Authors: B.H. Lee, Won Kyu Bang, Sang Ho Ahn, Chong Soo Lee
Abstract: In this study, optimum processing conditions for strip-cast AZ31 Mg alloy was investigated on the basis of processing map and microstructural analysis. To obtain the processing map, isothermal compression tests were carried out to a strain of 0.5 at temperatures of 200 ∼ 400°C with the strain rates of 0.01 ∼ 10s-1. It was found that maximum efficiency indicating the optimum processing condition occurred at 300°C and 10s-1. The possible deformation mechanisms operating at high temperature was also discussed.
Authors: Jie Xing, Xu Yue Yang, Hiromi Miura, Taku Sakai
Abstract: Low temperature superplasticity (LTSP) was studied in a fine-grained magnesium alloy AZ31 which was processed by multi-directional forging (MDF) under decreasing temperature conditions. Tensile specimens were cut from MDFed Mg alloy parallel to the final compression axis (CA), and the tensile axis perpendicular to the CA. Tensile tests was carried out at temperatures from 393K to 473K and at various strain rates. Superplasticity appears even at a low temperature of 393K with a stress exponent (n) of about 0.56 and a total elongation of 370%. The relative large stress exponent can be connected with grain coarsening taking place during deformation. The initial texture hardly takes place during deformation. This suggests that grain rotation does not occur during superplasticcity.
Authors: Li Qun Bai, Di Li, Bao Lan Guo, Min Guo
Abstract: The different chrome-free chemical conversion coatings were prepared on AZ91D magnesium alloy and SEM was used to observe the surface. The corrosion behaviors of die-casting AZ91D magnesium alloy with different coating in chloride environment were investigated by hydrogen gas evolution in immersion test, salt spray test and electrochemical measurement. The results showed that the corrosion resistance of magnesium alloy treated with two-step chemical conversion and sealing was the highest and was comparable with that of chromating, and followed by two-step chemical conversion treatment without sealing. The one-step chemical conversion treatment had the lowest corrosion resistance. Polarization and EIS characteristics in 5% NaCl solution depended on the type of surface treatment and correlated well with the order of corrosion resistance. Contrasted with one-step chemical conversion coating, the coating of two-step chemical conversion with sealing on magnesium alloy had more excellent corrosion resistance because the |Z| increased, the corrosion area was decreased and the time of the first pitting occurrence was prolonged. It is expected that this experiment can provide a foundation for designing more super chemical conversion coating to replacing the chromate conversion.
Authors: Xiao Shi Hu, Kun Wu, Ming Yi Zheng
Abstract: The effect of different alloying elements including Ni, Si and Al and various mass contents of these elements on the low frequency damping behaviors of magnesium alloys were investigated. The measurements of strain dependent and temperature dependent damping capacities of these magnesium alloys were carried out using dynamic mechanical analyzer (DMA), and the very different damping behaviors of these magnesium alloys were found. The hypoeutectic magnesium alloys with low solubility alloying elements such as Si and Ni shown extremely high damping capacities. But the Mg-Al alloys exhibited very low damping values. The tensile properties of these magnesium alloys were also illustrated in this study. It was found that hypoeutectic Mg-1.0%Si alloy possess the excellent overall properties with high damping capacity, relatively high tensile properties and good corrosion resistant ability.
Authors: Wei Huang, Di Li, Tian Liang Zheng
Abstract: Magnesium and its alloys have many applications for theirs excellent physical and mechanical properties. Due to magnesium’s active chemical properties and difficulties in direct painting, a novel environmental protective water based coating was developed, which mainly contains metal flake, silicate, silane and sodium polyphosphate etc. The properties and structure of the coating were investigated by adhesion test, hardness test, heat resistance test, neutral salt spray test and Scanning Electron Microscopy (SEM) et al. Meanwhile, the effect of sodium polyphosphate was also examined by hydrogen evolution test and electrochemical test. Furthermore, the film forming mechanism of the coating was explored by Fourier Transform Infrared spectroscopy (FTIR). Results showed that the coating had a stepped structure which could achieve extraordinary adhesion, 350°C temperature heat resistance, HV0.50/30 210 hardness and 300 hours anti-corrosion time in salt spray test. In the coating, the addition of sodium polyphosphate could greatly improve the corrosion resistance of the coating because of the barrier film formed by sodium polyphosphate. The mechanism of interpenetrating polymer network (IPN) was preliminary put forward based on the results of FTIR.
Authors: Tomasz Tański, Leszek Adam Dobrzański, Lubomír Čížek
Abstract: In this paper is presented the structure and proprieties of the cast magnesium alloys as cast state and after heat treatment cooled with different cooling rate, depending on the cooling medium (furnace, water, air). For investigations samples in shape of 250x150x25 mm plates were used. The presented results concern X-ray qualitative and quantitative microanalysis as well as qualitative and quantitative X-ray diffraction method, tensile tests, hardness measurement. In the analysed alloys a structure of α %solid solution and fragile phase β (Mg17Al12) occurred mainly on grain borders as well as eutectic and phase AlMnFe, Mg2Si. Investigation are carried out for the reason of chemical composition influence and precipitation processes influence to the structure and mechanical properties of the magnesium cast alloys with different chemical composition in as cast alloys and after heat treatment.
Authors: Ling Wang, Su Gui Tian, Keun Yong Sohn, Kyung Hyun Kim
Abstract: The mechanical properties and deformation features of AZ31-x%Sb alloys have been studied by means of the measurement of the ultimate tensile properties (UTS) and TEM observation. Results show that the UTS of AZ31 alloy is effectively enhanced to 297 MPa from 222 MPa, by additions of 0.84% Sb element, at room temperature, and the ultimate tensile strength of the alloy is still maintained up to 189MPa as temperature elevated to 200°C. Contrast analysis shows that the deformation mechanisms of AZ31-0.84%Sb alloy are twins and dislocations activated on basal and non-basal planes. The alloy displays the different deformation features at different deformation conditions.
Authors: G. Cao, S. Kou
Abstract: Hot cracking of ternary Mg-Al-Ca alloys in permanent mold casting was studied. The alloys are the base of some potential creep-resistant Mg alloys. The Mg-xAl-yCa alloys included Mg-4Al-1Ca, Mg-4Al-2Ca, Mg-4Al-3Ca, Mg-4Al-4Ca, Mg-5Al-3Ca, and Mg-6Al-3Ca. Constrained-rod casting was conducted with a steel mold. Rods were cast with their ends enlarged to act as anchors, which kept the rods from free contraction and thus induced tension in the rods to cause cracking during solidification. The susceptibility to hot cracking was evaluated based on both the widths and locations of cracks in the resultant castings. Both binary Mg-4Al and commercial alloy AZ91E, which is known to have a low susceptibility to hot cracking, were also included for comparison. It was found that within the composition range studied, the crack susceptibility decreased significantly with increasing Ca content (y) but did not change much with the Al content (x).

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