Applied Mechanics and Materials Vol. 685

Abstract: Pure ZnO thin films and Ag doped ZnO thin films were prepared on quartz substrates by sol-gel process. Structural features and UV absorption spectrum have been studied by XRD and UV-Vis-Nir scanning spectrophotometer. Taking phenol as pollutants, further study of the effect of different annealing temperature and Ag dopant amount of ZnO films on photocatalytic properties was carried out. The results showed that, the optimal annealing temperature on photocatalytic degradation of phenol in this experiment was 300 °C, the best molar ratio of ZnO and Ag was 30:1, which was better than pure ZnO film greatly. Excellent adhesion, recyclable and efficient degradation Ag doped ZnO thin films were found in this experiment.

Abstract: In order to improve the mechanical properties of A356 aluminum alloy in lost form casting (LFC), vibration and pressure were applied to solidification process of LFC, and the microstructures and the mechanical properties of the castings were compared with that of the castings in LFC without vibration and pressure. The results indicated that the grains of A356 alloy with vibration pressure in LFC became finer, and the dendrites decreased, and the equiaxed grains increased. At the same time, the porosities of the castings were significantly reduced. Compared with conventional LFC, the tensile strength, elongation, and hardness of A356 alloy with vibration pressure in LFC were all increased by 10% or above.

Abstract: Al-W alloy billets were produced by powder pressing at room temperature and subsequent hot pressing. Quantities of billets were compressed at constant strain rate and temperature with 60% height reduction on Gleeble-3800 thermal simulation testing machine to study the plastic flow behaviors of the test alloy. The temperature of the compression processes ranged from 450 to 570oC. The strain rate was varied between 0.001 and 1s⁻¹. The regularity of flow stress for the test alloy varied at elevated temperatures was studied. The activation energy during hot deformation is 757.943 kJ/mol by calculated, and the Arrhenius constitutive relation model was established. Keywords : Al-W alloy, powder metallurgy, thermal simulation, constitutive model

Abstract: Using the oxide of high melting-point and high stability to pin the grain boundaries is an effective method to improve the welding performance of the HSLA steel in this study. A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding calcium into the steel in the form of Si-Ca alloy. The effect of calcium addition on the cast microstructure of HSLA steel was analysed. The results show that the cast microstructure is mainly consist of lamellar and acicular ferrite, a small amount of pearlite and bainite. Compared with the original steel, there are acicular ferrites presenting in the experimental steel after adding 5 wt% Ca, which are the microstructure that we hope to get. The acicular ferrite will have a positive impact on the mechanical properties of the subsequent rolled steel.

Abstract: A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding calcium and magnesium into the steel in the form of Si-Ca alloy and Mg-Zr alloy, respectively. The effect of calcium and magnesium addition on the cast microstructure grain size of HSLA steel was analysed. The grain size of the cast microstructure in each sample was measured by the metalloscope observation method. The results show that a large amount of oxides generated from the adding Ca and Mg elements into the steel can accelerate the nucleation and refrain the grain growth, so the grains are refined. In the process of improving temperature, the oxides of Ca and Mg elements located in the interior of austenite can accelerate the nucleation and impede the grain growth. Almost every grain becomes finer after adding Ca and Mg elements. When adding 5wt% Mg, the mean grain size is the smallest, 0.712 mm, while the biggest grain size is 1.115mm in raw steel. The grain size in Mg 5wt% steel is refined by 36.1% in contrast with the raw steel. According to the adding amounts of Ca and Mg elements in experimental steel, the range of the mean grain size is from 0.712 mm to 0.975 mm.

Abstract: A new technology to obtain a fine-structured and high-toughness HAZ of HSLA steel for high heat input welding is developed using metallurgical thermodynamics, physical chemistry of metallurgy and material processing methods synthetically in this study. A kind of HSLA steel is designed in this experiment. The thermal stability second phase particles which would not be dissolved or aggregated at high temperature will be expected by means of adding calcium and magnesium into the steel in the form of Si-Ca alloy and Mg-Zr alloy, respectively. The effect of calcium and magnesium addition on the morphology and distribution of the inclusions in the cast microstructure of HSLA steel was analysed. The results show that the distribution of the inclusions is more dense and uniform with respect to the raw steel, and the size of the inclusions is smaller than the ones in the raw steel after adding Ca and Mg elements. Ca and Mg elements can accelerate the nucleation of the inclusions. The nucleation rate of the Mg element is relatively higher. The number of the inclusions in the adding Mg steel decrease more slowly relative to the adding Ca steel with the extension of the steelmaking time.

Abstract: In order to get the reasonable sinter basicity and suitable burden structures in Ansteel, the metallurgical performance of sinter, the softening-melting properties with different burdens were studied systematically in laboratory. The results show that, the reducibility and the reduction disintegration are improved, and the mineral compositions of the sinter become reasonable with the basicity increasing. When the basicity reaches 1.95-2.15, the burden structures with single sinter will achieve good softening-melting performance, and the maximum pressure maintains at a low level. When the sinter collocates with pellet and the basicity reaches 1.90-2.15, there will be narrow softening and melting zones and a low S property value. With the addition of natural lump ore, the softening zone will be widened and the melting zone will be narrowed, but burden’s comprehensive performance will be bettered. The assessment indexes obtained for the interactive reaction between burdens can assess the reasonableness of burden structure. Considering the reactivity index and the economic cost, the reasonable proportion of lump ores in blast furnace needs to be controlled within 15%-20%.

Abstract: In order to improve the qualities of sinter of Ansteel, the sinter’s metallurgical property was examined and analyzed that from the second workshop and the fourth workshop of ironmaking plant. And mineralogical composition and microstructure in high basicities sinter were investigated and analyzed by the X-ray diffraction, the optical microscope and the scanning electron microscope in laboratory. It was found that the differences between in sinter’s mineralogical composition and microstructures are according with the differences in chemical composition and the metallurgical indexes. Both the sinter’s minerals are mainly composed of hematite, magnetite or maghemite, calcium ferrite, dicalcium silicate, silicate glass phase. The content of the carbon in the fourth workshop is higher. So, it should decrease the content of the carbon that makes the microstructure of the sinter more rational.

Abstract: To solve the problem that the change of curve slop was not considered in the common corrosion fatigue crack growth, a new corrosion fatigue crack propagation model based on Pairs formula was established in this paper; which corrected parameters C and n of Paris formula at the same time. Based on the fatigue crack propagation experimental data of X70 pipeline steel in hydrogen sulfide corrosive environment, the key parameters of the model were fitted. Based on the new model, a FRANC3D software was used, and the corrosion fatigue crack propagation processes of X70 pipeline steel in corrosive solution were simulated. It was demonstrated that the simulated fatigue crack growth processes obtained by the boundary element method were very close to the test results, and the maximum error is less than 10%. Therefore, boundary element method can be used to predict the life of corrosion fatigue on the project.