Wen Jun Zhao

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.

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”.

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

Co-based high temperature alloys have been widely used in aeronautics and astronautics industry, because of its high strength at high temperature, excellent resistance of hot corrosion and oxidation. Unlike the traditional Co-based superalloys, strengthened by solution and carbide strengthening, the novel Co-Al-W superalloys are strengthened by a ternary compound with the Ll2 structure γ-Co3(Al,W). And the novel Co-Al-W superalloys showing high-temperature strength greater than those of conventional nickel-base superalloys, will become the candidates for next-generation high-temperature materials. We research alloying element Ta effect on microstructure of Co-Al-W superalloys by vacuum arc melting. Compare with the microstructure before and after adding alloying element Ta of Co-Al-W superalloy, we find that most of Ta element distributed in the γ-Co substrate phase, stabilizing and reinforcement the γ phase.

Research on Precipitation Phenomenon of TiC and TiAl3 Particles in Aluminum Melt

The Al-TiC and Al-TiAl3 master alloys were prepared by thermal explosion method of aluminum melt, and the precipitation phenomenon of TiC and TiAl3 particles were studied in aluminum melt through separate addition of Al-TiC master alloy and composite addition of Al-TiC and Al-TiAl3 master alloys into aluminum melt. The results show that: When TiC exists in the aluminum melt separately, its speed of sedimentation is fast, and after a shorter time of heat preservation, a large amount of TiC will precipitate; when TiC and TiAl3 coexist in the aluminum melt, the speed of precipitation will become slow, and after a longer time of heat preservation, only a small amount of TiC will precipitate; and before TiAl3 settles to the bottom of the sample, it will dissolve. The attenuation of the refining effect of Al-TiC and Al-TiAl3 is mainly caused by the precipitation of TiC and the dissolution of TiAl3.