Tian Dong Xia

An Investigation on Grain Refinement Mechanism of Master Alloys Al-Ti, Al-TiC and Al-Ti-C Toward Pure Aluminum

The grain refining effects of Al-Ti, Al-TiC and Al-Ti-C master alloys on commercially pure aluminum were compared, and the grain refinement mechanism of TiAl3 and TiC among master alloys was discussed. The results show that: the grain refinement of the master alloys Al-TiC and Al-Ti toward pure aluminum mainly stems from the heterogeneous nucleation role of TiC and TiAl3 particles, but with the extension of heat preservation time of fused mass, its role of heterogeneous nucleation will decline due to dissolution of TiAl3 and aggregation and precipitation of TiC. The preferable grain refinement effects of Al-Ti-C master alloys toward pure aluminum are mainly due to the fact that when TiAl3 and TiC particles are acted commonly as heterogeneous nucleation particles, the heterogeneous nucleation effect of TiC particles will be enhanced because of the presence of TiAl3.

Alloying Element Nb Effect on Microstructure of Co-Al-W Superalloy by Vacuum Arc Melting

Co-Al-W supperalloy used pure element powder, according to the ratio of different atomic percentage composition to make ingredients. It is mixed by planetary ball mill, pressed into blocks after the melting shape. Vacuum arc melting process was prepared by melting, after grinding, polishing, and after a volume of 5% perchloric acid and 95% of the electrolytic etcheing solution prepared in ethanol corrosion observed after analysis of the microstructure and phase composition by XRD analysis .It can be found that Co-Al-W superalloys were mainly composed of cobalt-rich matrix of austenite precipitation of γ phase and coherent with matrix of the L12 structure of γ′-Co3(Al,W) phase. In addition, Nb have effect on grain refinement and refine grain. Rockwell hardness test and analysis, It can be found that Nb can clearly improve the Co-Al-W superalloy hardness.

Kinetics Study on Non-Isothermal Crystallization of Amorphous Alloy Mg65Cu15Ag10Y10

The crystallization kinetics of amorphous alloy Mg65Cu15Ag10Y10 has been studied by differential scanning calorimetry in the mode of continuous heating annealing. It is found that both DSC curves and activation energy show a strong dependence on the heating rate. The activation energy for crystallization are determined as 186.1 and 184.4 KJ mol−1 for the heating rates β=5-20 Kmin−1, and 107.5 and 110.0 KJmol−1 for the heating rates β=20-80Kmin−1, when using the Kissinger equation and the Ozawa equation, respectively. Local activation energy at any volume fraction crystallized was obtained by the general Ozawas isoconversional method. The average value of local activation energy for heating rates ranging from 5 to 20Kmin−1 is 180.9 KJ mol−1 and for heating rates ranging between 20 and 80Kmin−1 is 110.2 KJ mol−1. Using the Suriñach curve fitting procedure, the kinetics mode was specified. The JMA kinetics is manifested as a rule in the early stages of the crystallization. The JMA exponent, n, initially being larger than 4 and continuously decreases to about 2 along with the development of crystallization. The NGG-like mode dominates in the advanced stages of the transformation. These two modes are mutually independent. The proportion between the JMA-like and the NGG-like modes is related to the heating rate.

Effects of Primary Si and Applied Load on the Dry Sliding Wear Behaviors of Hypereutectic Al-20Si Alloy

The effects of the primary Si phase and applied load on the dry sliding wear behaviors of hypereutectic Al-20Si alloy were investigated. The results show that coarse polygonal and star-like primary Si was refined into fine blocky shape by increasing superheat treatment temperature. The friction coefficient and wear rate significantly decrease after decreasing the size and changing the morphology of primary Si. Moreover, the friction coefficient and wear rate increase with the increase of applied load. Therefore, the wear properties are greatly influenced by the parameters like morphology and size of primary Si as well as applied load.

Research on Grain Refinement Effect of Al-5Ti-C Alloy on Pure Aluminum and its Attenuation Mechanism

The texture feature and grain refinement effect of Al-5Ti-C alloy on pure aluminum were analyzed and its attenuation mechanism was discussed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods.The results show that: Al-5Ti-C alloy is composed of Al, TiAl3 and TiC. Al-5Ti-C alloy has a good grain refining capacity for commercially pure aluminum. During the heat preservation process, due to precipitation of titanium compound in the aluminum melt, refinement effect of Al-Ti-C alloy is declined.

Effect of Cooling Velocity and Casting Temperature on Solidification Microstructure of Pure Al Refinement under Al-5Ti-B Alloy

The texture feature and grain refinement effect of Al-5Ti-B alloy on pure aluminum were analyzed and by adjusting the cooling velocity and casting temperature of molten aluminum,the influence of Al-5Ti-B alloy on solidification microstructure of pure aluminum was studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and other experimental methods. The results show that: Al-5Ti-B alloy is composed of Al, TiAl3 and TiB2. under the same solidified velocity,with the increase of the mass fraction of Al-5Ti-B alloy among the aluminum melt, solidification structure of pure aluminum equiaxed dendrite size small. But at the same additives of Al-5Ti-B alloy, the cooling rate and casting temperature have significant effects on the number and size of equiaxial crystal. Faster cooling rate and lower casting temperature of molten aluminum are favorable for the formation of thin equiaxial crystal of solidification microstructure.

Life-Cycle Energy Analysis as a Method for Welding Joint Design

This paper briefly explains some of the theoretical issues associated with life-cycle energy analysis and then uses an Al-Cu dissimilar metals welding product case study to demonstrate its use in evaluating alternative design strategies for an energy efficient welding product. The energy consuming characteristic and the life-cycle model of welding product have been studied by the energy analysis method. The energy consumption model of welding product throughout life-cycle has been modelled. The energy properties of different welding method has been studied and described quantitatively by the energy analysis method of total life-cycle. The results show that an effective brazing technology is the key to improve the utilization ratio of energy.

An Investigation on Vacuum Brazing of Dissimilar Nonferrous Metals of Cu and Al

The writer successfully obtained brazed Cu-Al joint by using vacuum brazing method, and also conducted an analysis for the microstructure morphology of the joint. The result shows that: The interface of the brazed Cu-Al joint includes three parts---the transition area on the Cu side, the central brazing seam area and the transition area on the Al side. Formed between the brazing seam area and the Cu substrate are the Cu3Al2 and CuAl2 layers, and the average width of the transition area of Cu3Al2 is 12 μm while that of CuAl2 8 μm. The brazing seam area is mainly composed of α-Al solid solution, Cu3Al2 and CuAl2 metal compounds, in addition, the ε-Cu15Si4 phase, the Al-Si phase and CuZn2 phase are also formed. These phases present themselves in the state of acicular compounds, which are dispersed in the brazing seam area.

Microstructure Evolution of Al-Ti-C Alloy Wires during Remelting Process

The regular pattern of evolution of TiC and TiAl3 during the remelting process of Al-Ti-C alloy wires was analyzed and the impact mechanism was discussed. The results show that: when the temperature of the remelting mass is at 730°C, with the increase of the heat preservation time of remelting, the degree of agglomeration of the original dispersed TiC will increase, and they are pushed toward crystal boundaries by α-Al during the solidification process, while TiAl3 will dissolve, aggregate, and grow. When the remelting temperature is at 1000°C, as the heat preservation time increases, not only the agglomeration degree of TiC increases significantly compared to that at 730 °C and the sizes and shapes of TiAl3 change significantly as well. The morphology of TiAl3 will change from being lump-and-short-rod-like to needle-and-flake-like. Before and after remelting, the Al-Ti-C alloys are both composed of TiAl3 and TiC, with no other phases formed.

The Formation Mechanism of Equiaxed Crystals in Pure Aluminum Solidification Structure under the Al-Ti-C Master Alloy

The influence of different solidified velocities on the structure of pure aluminum during the process of refinement by Al-5Ti-0.6C master alloy was studied and the impact mechanism was discussed. The results show that at the same solidified velocity, with the increase of the amount of Al-5Ti-0.6C master alloy, in the solidified structure of pure aluminum, columnar crystals will gradually decrease, while equiaxed crystals will gradually increase. But in the case when the level of addition is the same, the faster the solidified velocity, the greater the number of equiaxed crystals will be in the ingot microstructure. The formation of equiaxed crystals is the result of the dual role of dissociation of crystal particles and heterogeneous nucleation of “TiC particle---Ti transition zone”.