Hong Ming Wang

Behavior of β(Mg17Al12) Phases in Mg-Al Alloy Subject to Cycling Cryogenic Treatment

In Mg-Al alloy β (Mg17Al12) phase is the main precipitate and reinforced phase. The microstructure and performance of alloy are strongly dependent on the morphology and behavior of β phases. In this paper, a kind of Mg-Al alloy is chosen as the research object with 8.92 weight percent aluminum element. The alloy is subjected to cycling cryogenic treatment. The microstructure evolution and thermodynamic balance are analyzed by scanning electronic microscope and Thermo-CALC software. The results show that after two cryogenic treatments the quantity of the precipitate hardening β phase increases and the sizes of the precipitates are refined from 8~10 μm to 2~4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperatures and the significant plastic deformation due to internal differences in thermal contraction between phases and grains.

Microstructure of In Situ Al3Ti0.4Zr0.6p/Al Fabricated with Electromagnetic Field

The K2TiF6 ,K2ZrF6 powder and aluminum were selected as the raw materials to in situ synthesize the particulates reinforced aluminum matrix composites. During the fabrication process the electromagnetic field was imposed. The atomic ratio of Al/Ti/Zr in the particulates is determined as 3/0.4/0.6. The Al3Ti0.4Zr0.6 is a new kind of intermetallic compound, some properties of which fall in between those of Al3Ti and Al3Zr. Electromagnetic field plays an important part in fining particles and promoting their uniform distribution. When the electromagnetic induced intensity is 0.05T the particles have 0.5-2μm average size and uniform distribution in matrix. The crystal grains of matrix resemble equiaxed ones. The average size of grains are nearly 100μm, 50μm and 25μm when the electromagnetic induced intensities are 0, 0.025T and 0.05T seperately.

Compare the fluxing effect of boron sludge and CaF2 on CaO-based steelmaking slag

To reduce the pollution caused by employing CaF2 as fluxing agent in metallurgical flux, boron sludge is used as fluxing agent to substitute for CaF2. The melting temperatures of CaO-SiO2-Fe2O3-boron sludge system were investigated. The melting temperature of CaO-SiO2-Fe2O3-boron sludge slag system is increased with the increase of ω (CaO)/ω (SiO2) at first, and then fluctuates at about 1430°C. Moreover, the melting temperature of CaO-SiO2-Fe2O3-boron sludge system is decreased with the increase of boron sludge content at first and then increased, 7% content of boron sludge has the best fluxing effect and the melting temperature is1445°C. As a conclusion, the fluxing effect of boron sludge is close to CaF2, boron sludge may be considered to substitute for CaF2.

Preparation and Microstructure of Nano ZrB2 Reinforced Aluminum Matrix Composites

The ZrB2 particulate reinforced aluminum matrix composites were fabricated via melt direct reaction method using Al-K2ZrF6-KBF4 components. 850°C and 30 min were the optimized synthesizing temperature and reaction time separately. The metallurgical thermodynamic and kinetic processes were then analyzed in detail. It reveals that the interphases include Al3Zr, AlB2, [Z and [ atoms. The ZrB2 particulates can be acquired through the molecular combination between Al3Zr and AlB2 or atomic combination between Zr and B atomics. The in situ reaction between reactive salts and molten aluminum takes place spontaneously, which exhibits the character of liquid-liquid reaction. Scanning electronic microscope observation results demonstrate that the sizes of ZrB2 particulates are almost 100-200 nm. The intervals between particles are almost 200-400 nm, demonstrating a unirom status of distribution.

Calculation Model of Mass Action Concentration for CaO-B2O3-SiO2 Slag System

According to the coexistence theory of melted slag structure, a calculation model of mass action concentrations for CaO-B2O3-SiO2 slag system has been established, by which the mass action concentrations of all structure units in CaO-B2O3-SiO2 systems are calculated. The results indicate that the activities of CaO and 2CaO•SiO2 can be decreased effectively by B2O3. Furthermore, when the slag basicity is higher than 2.0, the activity of 2CaO•SiO2 increases firstly and then decreases with the increasing of B2O3 content. The activity of CaO increases with the increasing of slag basicity. When the basicity is less than 2.2, the activity of 2CaO•SiO2 increases with the increase of slag basicity. Moreover, when the basicity is 2.2, the activity of 2CaO•SiO2 reaches the maximum value. In another word, the activity of 2CaO•SiO2 decreases with the increase of slag basicity on the condition that the slag basicity exceeds 2.2. B2O3 exists in the slag in the form of CaO•B2O3, 2CaO•B2O3 and 3CaO•B2O3.

Effects of Rotational Inertia and Bearing Force on Stability of Permanent Maglev Rotator

The authors’ former works demonstrated that a passive magnetic (PM) rotator supported merely by PM bearings has a minimal speed, above which it can stabilize its equilibrium, under the function of a so-called Gyro-effect. It is unclear, however, by which factors is this minimal speed determined. This paper investigated the factors affecting the minimal stable speed of permanent maglev rotator, namely, the rotating inertia and PMB force. Two novel permanent maglev turbine models were designed: Model A---one stator and three rotors which have the same size but different rotational inertias; Model B---one rotor and one stator, but the stator has been devised with three different passive magnetic bearings: 1. a pair of small magnetic rings; 2. a pair of big magnetic rings; and 3. both of the two pairs of magnetic rings. Four Hall sensors distributed evenly at the turbine’s stator were used to detect the rotor’s eccentricity, and the speed sensor measured rotating speed. The calculated models of rotor’s eccentricity were established respectively for the two turbine models; the rotor’s eccentricity measuring system was built up and the rotor’s eccentricity of the two turbines was measured. The experimental data demonstrated that the rotational inertia of three rotors in the model A is 6.293×10-5 kg•m2, 1.074×10-4 kg•m2 and 2.081×10-4 kg•m2 respectively, and the corresponding minimal speed for suspension are 4597rpm, 3030rpm and 2222rpm respectively; in the model B, the magnetic force between the stator and rotor in the three cases is 92.12N, 123.48N, 212.66N respectively, corresponding to the minimal speed for suspension---3730rpm, 3120rpm and 2195rpm respectively. The results exhibited that same as the permanent maglev heart pump, permanent maglev turbines also have gyroscopic effect, which makes the rotors maintain stable suspension. And the minimal speed for suspension has a negative correlation with the rotor’s rotational inertia, namely, the bigger the inertia of the rotor, the smaller the required speed for suspension; the minimal speed for suspension also has a negative correlation with the magnetic force between the stator and rotor, that is, the larger the magnetic force, the smaller the rotating speed for suspension. Smaller minimal speed means better stability of the system, thereafter larger inertia or larger bearing force means better stability; besides, larger difference between minimal speed and performance speed of the rotator means better stability, it’s suggested permanent maglev be applied in high speed rotary machines.

Microstructure of In Situ Particles/7055Al Matrix Composites with Deep Cryogenic Treatment

Al2O3，Al3Ti and Al3Zr particles reinforced 7055 aluminium matrix composites were fabricated via melt reaction method. The volume fraction is controlled at about 4-5%. After extrusion and solution-aging heat treatment the sample was prepared for deep cryogenic treatment, The microstructure and evolution of mechanical properties of (Al3Ti+Al3Zr)p/7055 composites were analyzed using optical microscopy(OM),scanning electronic microscopy(SEM) and X-ray diffraction(XRD). Some θ(Al2Cu) phases with nanometer size precipitate in the inner grain. As some grains preferred orient the intensity of some main diffraction peaks increase. Compared with those of as-cast and squeezed states the micro hardness has increased by 16.8% and 10.0% separately.

Research on Activities of CaO-SiO2-B2O3 (Al2O3, Fe2O3) Slag System

A mathematical model on activities of CaO-based slag system has been established on the bases of ion-molecule coexistence theory of melted slag structure. The activities of CaO-SiO2-B2O3 (Al2O3, Fe2O3) systems are calculated. The effects of the content of B2O3, Al2O3 and Fe2O3 on activities are analyzed. The results indicate that the activities of CaO and 2CaO•SiO2 are decreased with the increases of B2O3, Al2O3 and Fe2O3. The effect of B2O3 is most remarkable. Moreover, the activity of CaO•SiO2 can be enhanced with increasing the contents of B2O3, Al2O3 and Fe2O3 respectively. These effects of Al2O3 and Fe2O3 are very similar, whereas the effect of B2O3 is most significant. As a conclusion, B2O3 is most effective to inhibit the formation of 2CaO•SiO2 as well as to promote the dissolution of lime.

Effect of Boron Mud on Melting Temperature of CaO-Based Steelmaking Slag

For the elimination of the fluorine pollution of steelmaking slag, boron mud is employed as fluxing agent for CaO-based fluorine-free slag. The effect of boron mud on the melting properties of slag is investigated. Hemisphere method is used to determine the melting temperature of samples. The results indicate that when the content of boron mud is lower than 7%, the melting temperature can be decreased by boron mud. With the content of boron mud increasing higher than 7%, the melting temperature is increased with increase of boron mud content. The basicity and the content of F2O3 have remarkable effect on the melting temperature of boron mud containing slag. When the basicity is in scope of 2.0-5.0, the melting temperature is in the range of 1350-1450°C correspondingly. The melting temperature of boron mud containing slag can be decreased significantly with increase of F2O3 content.

Characterization of (Al2O3)p/Al Composites In Situ Synthesized by Direct Melt Reaction Method

. (Al2O3)p/Al composites were in situ synthesized from Al-CeO2 system. The reinforcement phases, morphologies of particles and interfaces between particles and matrix were characterized by XRD, SEM, EDX, TEM and SAED. The in situ generated Al2O3 particles have various irregular shapes and disperse uniformly in matrix. The sizes of Al2O3 particles are normally less than 200nm. The interfaces between particles and matrix are clean. Moreover, there are large numbers of high density dislocations and the generated extensive micro-nano subgrains around Al2O3 particles. These novel characterizations contribute to the significant improvement of composites properties.