Key Engineering Materials Vols. 575-576

Abstract: The paper studied preparing sand-lime bricks by pressure shaping and nature curing, discussed the stimulation effect of compound activators composed of phosphogypsum and lime. The result shows that: when the proportions of raw materials are as follows: 10~15% weight content is iron ore tailings, 3% is phosphogypsum, 5% lime, 5% cement, 40~45% low quality fly ash, and 22~37% chips, the strength of sand-lime bricks produced gets its highest. XRD and SEM are used to characterize its mineral composition and microstructure. The paper also discussed the relationship between structure and performance inside the bricks, and its hydration mechanism.

Abstract: This paper is the result of research on preparation and properties of foam glazed thermal insulation mortar by means of orthogonal experiment method, the influence of main preparation process parameters on mortar’s dry density and compressive strength, and the optimum combination was obtained. The micro-structure of foam glazed hollow bead insulation mortar was analyzed by scanning electron microscope (SEM), and the mechanism of glazed hollow bead and foaming agent was preliminarily discussed.

Abstract: The research centers on the production process of high tensile 60Si2CrVNb spring steel for long service life with reference to the production conditions. Key points of the research lies in: long fatigue life and control techniques of non-metallic inclusions in melting process. Hot treatment process of spring steel also involves with the research, aiming to increase the strength of material by fining grain size by Nb element. The results confirms to the size of non-metallic inclusions can be controlled below 10μm with adoption of technologies of LF slag control and barium microalloy treatment in steelmaking process. The tensile strength can be over 2.0GPa and the elongation can reach up to 10% in the event that the quenching temperature is900°C and the tempering temperature is 410°C resulting obvious increase of strength and plasticity of spring steel.

Abstract: The melting temperature of CaO-SiO₂-B₂O₃-(boron mud, CaF₂) slag system was investigated. The slag melting temperature was measured by using the hemisphere method. The results indicate that B₂O₃ has a significant fluxing effect on the slag system. When 1%-11% B₂O₃ was employed as fluxing agent, the melting temperature of the slag changed from 1525°C to 1200°C. When the content of B₂O₃ is 5% and the range of basicity is 1.5~3.5, the melting temperature of the slag increases with the increase of the basicity. However, when boron mud or CaF₂ was added to the slag, the melting temperature of the slags decreased with the increase of addition at a fixed B₂O₃ content (5%) and a fixed basicity (R=2.5). Furthermore, the melting temperature of the slag system which contains CaF₂ is lower than the slag system which contains boron mud.

Abstract: 7055 aluminum alloy was processed by circular cryogenic-aging treatments for four times. Some characters such as precipitates, dislocation density, crystal structure and micro hardness were studied in detail. It is showed that the sizes of precipitates are decreased from several hundred nanometers to 100nm with the increase of cycle index. The main components are AlZn or AlZnMg phases. The hardness test result illustrates that the micro hardness arrives at 232HV after circular cryogenic-aging treatment for twice. The corresponding precipitates exhibit high density and complex sizes. The sizes are in the range of 50-200nm.

Abstract: The thermodynamic condition and behavior of precipitates were discussed about the Al₂O_{3 p}/7055 composites subjected to cryogenic treatments. A kind of software named Thermo-Calc was employed to calculate and analyze the mass amount of several main precipitates based on the thermodynamic balance theory. The results demonstrate that when the temperature decreases from 300K to 77K the precipitated amount of T(AlZnMgCu) and θ (Al₂Cu) phases will increase. For S(Al₂CuMg) phase, at 175K there is a transverse point from increasing tendency to the opposite. It should be noted that η (MgZn₂) is the main precipitated phases in compistes ,which accounts for more than eleven weight percent in one mole material. But the balance mass amount lower a little from 300K to 77K. It is analyzed that the volume shrinkage and lattice contract are the main driving forces for precipiting. Due to the difference of heat expansion coefficient among various phases the anisotropic shirinkge lead to micro voids that will act as the nucleation cores,which faciliate the precipitation.

Abstract: 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.

Abstract: In order to make clear about the effect of cryogenic temperature on the microstructure evolution of alloy, the as-cast AZ91 magnesium alloy was subjected to the cryogenic treatment after solution treatment (415°C,5h) and aging treatment (190°C, 16h) with the protection of graphite power. Transmission Electron Microscope was utilized to characterize the microstructure of as-treated sample. The results show that a high volume fraction of nanocrystalline can be found in the treated alloys with the average sizes are about 55nm. The phenomenon highlights the importance of cryogenic temperature in forming nanostructures. During the continuous contraction of alloy the micro dynamic plastic deformation induces the generation, movement and accumulation of high-density dislocations that give rise to the formation of nanocrystalline during recovery and recrystallization.

Abstract: 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.

Abstract: In this paper, we use the High rate solidification to study process parameters and CMSX-6 super-alloy solidification structure. And then, it can provide more basis for the industrial directionally solidified casting of superalloys blades. The results show that: under certain process parameters, it can be obtained parallel columnar crystals directional solidification structure. The organization is composed of the matrix γ phase and the secondary precipitated γ ' phase; under an optical microscope, it can be observed the shrinkage porosity due to the volumes reduction arising solidification.