Materials Science Forum Vol. 1026

Abstract: The novel titanium alloys were investigated in this article. The Ti-3573 and Ti-3873 titanium alloys were cold rolled and aged for different times at 650°C. The microstructure and mechanical properties of the samples were observed and measured, respectively. The results show that the mechanical properties of Ti-3873 alloys were better than those of Ti-3573 alloys. The cold rolling accelerated the α phase precipitation effectively. Stress-induced martensitic transformation was observed in both titanium alloys after cold rolling and aging treatment. Better aging strengthening effect can be obtained for the Ti-3873 titanium alloy which contains more molybdenum element, it is attributed to the role of Mo as β phase stable elemen. The tensile strength of Ti-3873 titanium alloy after aging for 3h reached the maximum value (1314MPa).

Abstract: In order to eliminate the out of round defect of grinding ball, an improvement measure is proposed. Firstly, the wear behavior and mechanism of the ball in different service conditions are obtained. Then, the root cause of grinding ball out of roundness is discussed. Finally, the corresponding improvement measures are put forward from the aspects of grinding ball material and heat treatment, so as to improve the microstructure and properties of grinding ball.

Abstract: The metastable beta titanium alloy Ti-3Al-5Mo-7V-3Cr (Ti-3573) was used as experimental material in this paper. Different cold rolling reduction was conducted in this titanium alloy. The results show that the total elongation (A₅₀) reached maximum value of 16% after 30% cold rolling. The tensile strength reached maximum value of 910 MPa when the cold reduction increases to 50%. Microstructural evaluation suggested that the precipitation of α phases, deformation twin and stress-induced martensite is responsible for the enhanced tensile properties. Moreover, the TRIP/ TWIP deformation mode contributes to the improvement of the ductility of the titanium alloys.

Abstract: The fatigue crack growth of Al-Zn-Mg-Cu alloy can be adjusted by different aging treatments. In the present work, a high Zn-containing Al-Zn-Mg-Cu alloy was treated by single, double and triple stage aging treatments and typical T6, T79 and T77 states were selected by tensile properties. Fatigue crack growth under these aging states was tested and related fracture morphology and precipitation characteristics were observed. The results showed that fatigue crack growth resistance for the alloy was T6<T79<T77. The corresponding fracture morphology also showed the difference of fatigue striations and the measurement of them provided an additional evidence. The precipitation proved that the alloy with T6 state possessed GPI zone, GPII zone and η' phase while that for T76 state was GPII zone, η' phase and η phase. As for the T77 state, the precipitate types were GPII zone and η' phase. The matrix precipitate for T6 state was smaller and denser than that for T79 and T77 states while that for T77 state possessed a dense distribution than that for T79 state. The measurement of precipitate size distribution also proved it. The grain boundary precipitates for T79 and T77 states were similar, which had a more intermittent distribution than that for T6 state.

Abstract: Wire electric discharge machining non-contact machining process based on spark erosion technique. It can machine difficult-to-cut materials with excellent precision. In this paper Alloy-X, a nickel-based superalloy was machined at different machining parameters. Input parameters like pulse on time, pulse off time, servo voltage and wire feed were employed for the machining. Response parameters like cutting speed and surface roughness were analyzed from the L25 orthogonal experiments. It was noted that the pulse on time and servo voltage were the most influential parameters. Both cutting speed and surface roughness increased on increase in pulse on time and decrease in servo voltage. Grey relation analysis was performed to get the optimal parametric setting. Response surface method and artificial neural network predictors were used in the prediction of cutting speed and surface roughness. It was found that among the two predictors artificial neural network was accurate than response surface method.

Abstract: The effect of different additives Ni, Fe, Cu on the structure and properties of electrolyte system 78% Na₃AlF₆- -9.5%AlF₃-5.0%CaF₂-7.5%Al₂O₃ at 1200K and 1.01Mpa was studied by molecular dynamics method. The radial distribution function, coordination number, diffusion coefficient, conductivity, and viscosity of the system were discussed in detail. The results demonstrated that the order of the self-diffusion coefficient of ions in the electrolyte system is: Na⁺ > F^- > O^2- > Ca²⁺ >Al³⁺. The addition of Ni and Fe connected the free aluminum composite ion groups in the system through fluorine bridges, which enhanced the interaction between Al³⁺ and Al³⁺. The addition of Cu weakened the interaction between Al^{3 +} and Al³⁺ and the F^-. The interaction between Al³⁺ and Na⁺, [AlF₇]^4- ionic groups might appeared in the melt system. After adding NiO, Fe₂O₃, and Cu, the electrical conductivity of the system increased, and the viscosity decreased. The research work revealed the influence of Ni, Fe, Cu on the ion existence form, mobility, inter-ion interaction and diffusion mechanism of cryolite molten salt system, which has important guiding significance for aluminum electrolysis production.

Abstract: The annealing temperature is a key parameter for the mechanical properties and microstructure control of the 2195 Al-Li alloy sheet in the annealing process. In the present study, the effect of annealing temperature on the microstructure of 2195 Al-Li alloy sheet was investigated using a general mechanical testing machine, scanning electron microscope (SEM), transmission electron microscope (TEM), and backscattered electron microscope (EBSD). It was found that the optimized annealing temperature for 2195Al-Li alloy sheet of H112 state is 400°C, the alloy sheet shows the satisfactory mechanical properties. In addition, with the increase of annealing temperature, the δ' phase, the θ' phase and the T1 phase are formed in the alloy sheet, which leads to the strength of the alloy increase. Furthermore, the annealing temperature obviously affect the texture component and intensity during annealing treatment process.

Abstract: The press hardening steel with thick specification has been used as automobile chassis parts. With the increase of the thickness, the cooling rate of the inner core is lower in the conventional process, resulting in a poor harden ability, and the fatigue test is not qualified. In this study, the microstructure of hot forming parts with thick specifications was studied by means of metallographic and micro-hardness testing. The results show that there is a microstructure gradient in the thick hot forming parts, which leads to the uneven strength in the cross section and finally affects the fatigue test results.The finite element analysis method is used to study the cooling rate of the inner core of the hot forming parts. The high hardenability press hardening steel products has been prepared by adjusting the components.

Abstract: Both microstructure inhomogeneity and mechanical property diversity along the thickness direction in rolled thick aluminum plates have been considered to have a remarkable impact on the performance and properties of the products made from the plates. In this study, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) characterizations of microstructure and texture types along the thickness directions of Al7055 thick plate specimens prepared using two conditions, hot-rolling and solution-quenching, were performed. To examine the mechanical properties, uniaxial tensile tests were also carried out on specimens machined from both types of thick plates, using a layered strategy along the thickness direction. The results indicate that both the microstructure and mechanical properties are inhomogeneous under the two conditions. Furthermore, it is evident that there is a hereditary relationship between the mechanical properties of the two plates—areas with higher yield strength in the as-hot-rolled plate correspond to areas with the higher yield strength in the as-solution-quenched plate