Advanced Materials Research Vols. 154-155

Abstract: The hot compression behavior of ZK60 magnesium alloy was investigated at the temperatures from 523 to 673K and strain rates from 0.001 to 1s-1 on Gleeble-1500 thermal simulator. The results show that flow stress of ZK60 magnesium alloy decreases with the increase of deformation temperature and the decrease of strain rate. The flow stress curves obtained from experiments can be described in four different stages, i.e., work hardening stage, transition stage, softening stage and steady stage. For higher temperature and lower strain rate, the transition and softening stage are less obvious. The onset of dynamic recrystallization (DRX) occurred before the stress peak in true stress-true strain curves. The critical stress characterizing the onset of DRX rises with the increase of strain rate and/or the decrease of deformation temperature. The constitutive equation of ZK60 magnesium alloy during hot compression was constructed allowing for the effect of true strain on materials constants. The predicted stress-strain curves according to the constitutive equation are in good agreement with experimental results.

Abstract: For the better application of the solid carburized processing with simple technology, easy operation, safety and reliability, economic mode, this paper studied the carburized layer of Fe-1.57W binary alloy after solid carburized treatment by OM, SEM, EDS, XRD. Its microstructure was observed and analyzed, and its surface hardness and hardness gradient in the section were measured. At the same time, the formation mechanism and morphology causes of WC were researched and conjectured from the thermodynamics, the crystallography and the valence electron. The results show that: After 930 °C × 8h solid carburized processing and water quenching, the surface hardness of the carburized layer of Fe-1.57W binary alloy is up to HRc59, and its microstructure is composed by M, γ, Fe3C and WC. Fe3C lies in the surface carburized layer. In adjacent layer, there is a layer with large size WC. At 930 °C, WC nucleates on {100} crystal planes in the austenite, and grows along the c-axis direction, under the mutual restriction among the crystal faces of (11 0), ( 2 0) and (2 0) or in the parallel crystal faces of (11 0) and ( 20), and then shows as thin strip, triangle, square, bow-shaped morphology, etc.

Abstract: In this paper, a quantitative analysis for the micro geometrical characteristic of rough surface profile is researched with the fractal theory. Firstly, the fractal dimensions of profile curves under different surface roughness are obtained by using the vertical section method, and then the theoretical relationship between the surface roughness and the fractal dimension is built. Secondly, according to the surface profile curve composed of many triangle peaks, the angles and heights of them are calculated to study the micro geometrical size. Through their variation laws changing with the fractal parameters, the calculation formulas of their average values related to fractal dimension are obtained by using mathematics regression tools. Finally, combing three theoretical relationships built above, the geometrical characteristic of the rough surface profile can be calculated with the surface roughness and accuracy requirement known.

Abstract: The linear friction welding (LFW) performance of hydrogenated Ti-6Al-4V alloy was investigated. The effects of hydrogen on macro-features and axial shortening as well as microstructure of Ti-6Al-4V alloy joints welded by LFW were analyzed. The mechanical properties of joints after dehydrogenation were also examined by tensile test at room temperature. The results indicated that the hydrogenated Ti-6Al-4V specimens containing 0.3~0.4 wt% hydrogen had a better microstructure and plastic deformation ability, which resulted in the optimum welding performance improvement of LFW. The critical power input of LFW could be lowered by addition of hydrogen to Ti-6Al-4V alloy. The results of tensile test showed that joints which experienced thermohydrogen processing possessed the same tensile strength and plasticity as original joints.

Abstract: Iron and manganese oxides/granular activated carbon composite (GACFM) was prepared via a chemical coprecipitation route, followed by a heat treatment at elevated temperature. The as–prepared GACFM was characterized by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). The main iron and manganese oxides actually present in the composites were mainly composed of Fe3O4 ,Mn3O4 and (FeO)x(MnO)1-x. The adsorption and catalytic properties of GACFM and some conditions effects such as H2O2, pH , temperature and CO32- were studied for the removal of 2,4,6-trichlorophenol (TCP) from aqueous medium. The adsorption of TCP on GACFM obeyed the Freundlich isotherms. When the initial concentration of H2O2 was 0.4mg/L , 5mg/L TCP removal rate was maximum on the GACFM. The treatment of TCP could be carried out at initial pH under 7.0. CO32- can scavenge •OH in solution and decreased TCP removal. In the whole, GACFM was satisfactory absorbent and catalyst for the removal of chlorophenol from water.

Abstract: With the development of science and technology, the higher and higher surface accuracy of workpiece is required. The characterization of surface topography affect greatly on functional performance of workpiece. In recent years, many researchers have made a large progress on the study of surface topography and presented some related standards. The assessment of parameters of surface roughness, however, has not been researched intensively in the new generation of standards system. This paper proposes a novel roughness separation method based on B spline wavelet to analyze engineering surface. This method improves accuracy of roughness signal separation. The experimental results show that B spline wavelet can extracts accurately the roughness component and experiment results by the proposed method fit with the actual value of the standard sample plate.

Abstract: In order to provide theory basis and experimental evidence for optimizing milling parameters, the cutting force prediction models for milling of Ti6Al4V with uncoated cemented carbide tool were built based on single factor method. The significances of the cutting force prediction models were checked. The effects of milling speed, feed per tooth, milling depth and milling width on cutting forces were also studied. The results show that the built prediction models can be applied effectively to predict the cutting forces in milling of Ti6Al4V in the experiment parameters range. Milling depth has highly obvious influence on cutting forces among these milling parameters. The cutting forces decrease with the milling speed increasing, and increase with feed per tooth, milling depth and milling width.

Abstract: This paper set a numerical calculation model with local mesh refined for laser welding of titanium alloy applying body heat source model which can accurately describe the shape of keyhole and molten pool on laser welded joint. It calculated the change patterns of the temperature distribution and heat conduction in region of gas, liquid, and solid phase under different laser energy density on the stage of heating and cooling. The results showed that with the increase of the laser energy density t, the dimension of keyhole and molten pool, the temperature gradient and the duration of gas and liquid phase on the stage of heating and cooling are all expected to increase. Under the same laser energy density, temperature gradient has a maximum value in the region of gas phase, secondly is in liquid phase, and minimum in solid phase.

Abstract: A pulsed magnetic field (PMF) was introduced into the solidification of pure magnesium and the effect of structure refinement is investigated. The results show that remarkable microstructural refinement is achieved when the pulsed magnetic field is applied. The morphology is characterized as the columnar grains at the periphery and equiaxed grains at the core. The average grain size in the center of ingot is refined to 260m at the optimal processing parameter (5Hz, 200V). The pulsed magnetic field increases melt convection during solidification, as a result, the stress fractures the dendrites inwards from the mould wall, and the fractured dendrites act as nuclei, so the big columnar grains are prohibited.