Advanced Structural Materials, IUMRS-ICA 2010

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Authors: Wei Hong Li, Yuan Sheng Yang, Chang Wen Tian, Shou Qiu Tang, Ji Xue Zhou, Li Kun Jiang
Abstract: Long route and high inclusion content are two common problems existing in the present process for magnesium alloys. To solve these problems, a new process technology, in which the crystalline magnesium is used as the raw material, is developed. The process is melting flux→ adding raw materials in batches → stirring→ holding→ pouring (MASHP). The mechanisms of protection and purification mechanisms are also analyzed. The results show that the MASHP process has high protection and purification effects on magnesium alloys. By the in-batches addition mode of raw materials, no oxidation and evaporation loss of magnesium produce during heating and melting, and the inclusions that self-contained in the crystalline magnesium and that produced by oxidation during heating and melting can be minimized. High quality magnesium alloys can be produced by the new process.
Authors: Ya Qin Yang, Zhi Min Zhang, Bao Cheng Li
Abstract: The precipitation mechanism of secondary-precipitated phase β in AZ80 magnesium alloy during the hot compression deformation under different temperature was investigated. The results show that there are β-Mg17Al12 phases with different morphology and precipitation mechanism in the microstructure of AZ80 alloy deformed both in two-phase region、critical region and single-phase region. β-Mg17Al12 phases were directly deformed and broken to be strip form during the compression under 200、250、300 and 350°C. A lot of fine granular second phase particles precipitated with the grain refinement simultaneously in AZ80 alloy deformed in two-phase region with tremendous deformation. There are also fine granular second phase particles precipitated in the alloy deformed in critical region. There are massive β-Mg17Al12 phases precipitated in the alloy deformed under higher temperature such as 350 and 400°C during the water cooling after the compression, the high power observation of which is fine and tightly lamellar microstructure. Compared with coarse reticular β-Mg17Al12 phases in the as-cast microstructure of AZ80 alloy, the morphology of β-Mg17Al12 phases precipitated during the hot compression has obvious improvement.
Authors: Su Qiu Jia, Wen Ke Gao, Zhan Kui Zhao
Abstract: The Corrosion behaviour of Mg-7.3Al alloy in buffered chloride solutions was investigated in the paper. The corrosion resistances of Mg-7.3Al alloy were evaluated in different borate capacity and pH by immersion test and polarization curves. The influences of immersion time, pH and buffer borate capacity were analyzed. The results revealed that the corrosion rate of Mg-7.3Al alloy depends on the pH of corrosive solution and has no relationship with buffer capacity. In the pH 6.5 and 2g / L buffer solution, the morphologies of Mg-7.3Al alloy consist of porous pits and protuberant second phases. There are seriously corroded area and macro-uncorroded area or protuberant second phases on the sample surface. The corossion potentials of the mg alloy is kept the same value in the pH 9 solution, regardless of borate capacity is 1g/Lor 2g/L, which are higher than that in the neutural chloride solution or acid solution (pH=6.5). Borate may play an inhibition role for mg alloy by the quick corrosion test of polarisation curves.
Authors: Ding Fei Zhang, Li Bo Cui, Yu Ping Liu
Abstract: The effect of different factors on the corrosion performance of the anodic film formed on AZ31 was studied by using electrochemical impedance spectroscopy (EIS) and Tafel polarization curves techniques. The result of EIS showed that the oxide film formed at 20 mA·cm-2 had the highest corrosion resistance and the optimum temperature was 40°C. The similar conclusion was drawn by the Tafel polarization curves. Moreover, the equivalent electrical circuit R(C(R (QR))) (CR) was used to analyze the EIS data.
Authors: Xian Long Cao, Fu Sheng Pan, Hong Da Deng, Wei Cai
Abstract: This present work investigated the corrosion behavior of AZ31 magnesium alloy substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane modified with cerium nitrate. The corrosion behavior of the pre-treated substrates in 0.005M sodium chloride solutions was assessed by potentiodynamic polarization, open circuit potential and electrochemical impedance spectroscopy (EIS). The results showed that the silane pre-treatments improved the corrosion resistance of the AZ31 magnesium alloy substrates in the presence of chloride ions. Especially the addition of cerium nitrate played an important role in reducing the corrosion activity.
Authors: Zhi Qiang Zhang, Qi Chi Le, Jian Zhong Cui
Abstract: Effects of low frequency electromagnetic field on surface quality, microstructure and hot-tearing tendency of direct chill casting of Φ500mm ZK60 magnesium alloy billets were investigated. The results show that with the application of the low frequency electromagnetic field, the surface quality of Φ500mm ZK60 magnesium alloy billets has been markedly improved, and the depth of cold fold is decreased. In the conventional direct chill casting, the microstructures of the billet, especially at the center, are coarse. The distribution of the grain size is non-uniform throughout the billet. From the edge to the center, the microstructure gradually changes from fine to coarse in all billets. However, under the low frequency electromagnetic casting, the microstructures of the billet is significantly refined, the distribution of the grains size is relatively uniform from the billets edge to the billets center. And it also shows that the hot-tearing tendency of direct chill casting Φ500mm ZK60 magnesium alloy billets under low frequency electromagnetic field is significantly reduced.
Authors: Zhuang Qing Zhu, Fu Sheng Pan, Chong Zhao, Yao Bo Hu
Abstract: AZ31 wrought alloys at as-cast state with different microcontent calcium and strontium was studied by optical microscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The study shows that the primary dendrite spacing and the secondary dendrite arm spacing can be refined significantly by Ca or Sr element. At 0.5wt.% Sr and 1.8wt.% Ca, the best refinement effect is fulfilled, its primary dendrite spacing and secondary dendrite arm spacing decreased from 292μm to 87μm. The Al4Sr intermetallic compound is observed at grain boundaries When Sr was added. The Al4Sr disappears after Ca added, a new ternary intermetallic compound (Mg, Al)2Ca presents. The addition of Sr and Ca can cause microhardness increasing.
Authors: Xin Huang, Guang Jie Huang, Dong Ping Xiao, Qing Liu
Abstract: In this paper, the influence of clock rolling(CR)on microstructure and texture as well as the anisotropic properties of AZ31 alloy sheet was systematically studied. Compared to unidirectional rolling(UR), clock rolling leads to more uniform microstructure in annealed sample. The average grain sizes of the two kinds of sheet are similar. Texture measurement reveals that clock rolling can effectively weaken the intensity of basal texture and generate more symmetrical basal texture. Clock rolled samples exhibit weaker anisotropy of mechanical properties due to its lower basal texture intensities and more symmetrical basal texture in tensile test.
Authors: Da Heng Mao, Guan Zhong Zhao, Jian Ping Li, Jian Bing Hu, Sheng Fang Zhang
Abstract: With composite energy-field of ultrasonic field and electromagnetic field introduced into the roll-casting process,AZ31B magnesium alloy has been acquired successfully,during this process,the effect of composite field on structure and properties of AZ31B magnesium roll-casting alloy are studied. The result shows that the composite field can decrease the grain size greatly from 60-80μm to 12-18μm compared with the conventional roll-casting(without out-field), improving the tensile strength and yield strength by 13% and 35% respectively and the elongation increased by 82.2%(average value).Meanwhile,the microstructure of magnesium alloy obtained with the composite field are more uniform after annealing,mechanical properties are improved greatly as well.

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