Advanced Materials Research Vols. 299-300

Abstract: Foam magnesium alloy was an idea substitute of hard tissue of human bodies because its elasticity module was close to the bone of human. In the paper, foam degradable magnesium alloys were prepared by “Press-Dissolution-Vacuum sintering-Hot treatment-Aging” powder manufacturing process firstly. Then samples were coated by immersion in a bath containing phosphate and rare earths lanthanum. Results show that, Mg-0.9Mn foam magnesium alloys after hot treatment had better anticorrosion performance; and coated foam magnesium alloys form the bath with phosphate lanthanum chloride had lower rate of degradation.

Abstract: Warm deep drawing processing was used to improve the deep drawability of Twin Roll Cast AZ31B magnesium sheet. Conspicuous effects were obtained and the Limited Drawing Ratio value of the sheet was improved by about 50% after the pre-deformation. Influence factor on the drawability of Twin Roll Cast magnesium alloy sheet was also analyzed. Numerical simulation method and microstructure analysis method were used to discuss the mechanisms of formation and develop of Twin Roll Cast microstructure in the twin roll cast process and the pre-deformation process.

Abstract: The effect of DC gradient magnetic field and the sectional solidification on the structure of Al-Fe hypoeutectic alloy was investigated. The experiment results showed that the morphology and structure of the sample were homogenous, when it was bulk solidified without magnetic field. When the sample was sectionally solidified without magnetic field, the upper part had less iron content, bigger dendritic trunk and less interdendritic precipitate. When the sample was sectionally solidified in the gradient magnetic field, the above-mentioned differences between the upper and lower part were more prominent. The physical essence of the experiments was analyzed with quantum mechanics and solidification theory.

Abstract: The equilibrium phase relationships and compositions of Ni - 51at.%Al/Ni - 26at.%Al diffusion couple heat treated at 650 °C for various times have been investigated by means of diffusion couple technique. Experimental results showed that Ni₅Al₃ phase was not only stable at 650 °C, but also had a large solubility range (45.3～40.6) at.% Al. The obtained relationships of NiAl/Ni₅Al₃ and Ni₅Al₃/Ni₃Al are in accordance with the current generally accepted Ni-Al binary system phase diagram, but their composition ranges are quite different from the presently accepted one, that is, the the phase boundaries of NiAl / (Ni₅Al₃ + NiAl), (Ni₅Al₃ + NiAl) / Ni₅Al₃ and Ni₅Al₃ / (Ni₃Al + Ni₅Al₃) significantly shift to the Al-rich side.

Abstract: Under high pressure of more than 1GPa, the grain growing process of Zinc-Aluminium (ZA) alloy is difficult observed by experimental method, therefore numerical simulation method is used to observe grain growing process of ZA alloy. Pressure as a important variable is leading-in thermodynamic parameters of ZA alloy, then solute diffusion and redistribution model, grain nucleating and growing model are present, and dendrite growth module is applied to describe grain growth. The simulation results of grain growth process under high pressure are demonstrated: In the initially solidification stage, grains are equiaxed growing process, after 15s solidification time, dendrite arm size are not equal, the reason is there are nonhomogeneous temperature fields around grains, which make some grains appear fast growing velocity, even it can be observed that dendrite arm of different grains are meet each other at 25s solidification time. Comparing simulated microstructure with experimental microstructure under 2GPa high pressure, it shows both grain size and grain distribution are similar, proving that the grain growing process can be well observed by simulation method.

Abstract: Hypereutectic Al-Si alloy are desirable and promising for many structural applications. The influences of electric pulse parameters on Al-22%Si-1.5%Cu alloy by using OM (optical microscope) analysis along with wear test had been investigated. This work focused on studying the comparison of its solidification structure and wear resistance property with and without electric pulse treatment, respectively. The results indicated that EPM (electric pulse modification) treatment with different voltage parameters along with the frequency parameters both had the remarkable effects on micro-structure, and the grain size of alloy was refined gradually with the increase of pulse voltage or frequency. The wear resistance property of the alloy was enhanced by electric pulse treatment. It was observed from DSC cooling curve that the precipitation peak point of primary silicon was delayed by electric pulse modification comparing to the original sample without electric pulse treatment, which was analyzed to play a critical key in the alloy grain refinement.

Abstract: The C/C-SiC composites are prepared by the reaction molten infiltration process of silicon powders, using porous C/C composites as preform. C/C composite frameworks with various bulk densities are prepared by the chemical vapor infiltration (CVI) combined with the resin impregnation-pyrolysis methods, using needled-carbon fiber felts as preform. Characterization of the microstructure was conducted with a digital microscope (VHX-500) and a polarized light microscopy, respectively. The hardness (H) and the elastic modulus (E) of the composites are measured using a nano indentor. The results show that the indentation behaviors of the pyrolytic carbon and resin carbon are elastic while silicon and silicon carbide show a plastic deformation behavior. The hardness of the resin carbon as well as the pyrolytic carbon is 2.1GPa and 1.3~1.6GPa, respectively. E of SiC varied from 360 to 259GPa and H from 36 to 21GPa. For Si, the value of E and H are 155-170GPa and 11.7GPa, respectively. The relationship between microstructure and mechanical properties of C/C-SiC composites were analyzed.

Abstract: 360MPa grade heavy plate with high performance was developed through TMCP technology. By means of tensile and charpy impact tests and optical microscopy, the effects of processing parameters on final microstructure and properties of the steel have been studied, such as start rolling temperature in austenite non-recrystallization region and cooling rate. In order to obtain better mechanical properties, the optimization of the rolling process in an experiment rolling mill has been carried out. It has been found that the tensile strength of HSLA heavy plate are significantly improved by decreasing the start rolling temperature and increasing of the cooling rate, but the impact properties present the reverse law.

Abstract: Based on the empirical electron theory in solids and molecules (EET), the statistical value of phase structure formation factor (S') was calculated by using the calculation methods of statistical value of alloying valence electron structure parameters. The effects of alloying elements upon austenitic zone of Fe-C phase diagram were discussed. The results show that: 1) Mn and Ni can increase the S' value of γ-Fe and austenitic phase, which increase their stability, leading to expand the γ-zone; 2) Cr, Mo and Si can increase the S' value of ferrite and cementite, which make them easier to precipitate, leading to reduce γ-zone. The research results agree well with real situations.

Abstract: To meet the requirements of super-high speed vitrified bond of CBN grinding wheel that should be low-melting, high strength and multi-foams, performance of nano-ceramic bond were researched in this paper. Four types of bond which major glass components was R₂O+RO-B₂O₃- -Al₂O₃-SiO₂ have been compounded with pure raw chemical materials. In order to improve the strength of bond, nano-materials were added into formulations of the vitrified bond. And experiments results showed that compared with traditional vitrified bond the new nano-ceramic bond had a significant advantage at its refractoriness, expansion coefficient, surface morphology and bending strength. Especially, the bending strength of 4# nano-ceramic bond had reached to 83.75 MPa and its refractoriness was 790 °C. It proved that 4# nano-ceramic bond was more suitable for super-high speed CBN grinding wheel.