Advanced Materials Research Vols. 189-193

Abstract: AZ31 magnesium alloy profiles were prepared by continuous rheo-extrusion process, and effects of solution and aging treatments on the microstructures and mechanical properties was investigated by OLYMPUS optical microscope, scanning electron microscope, energy dispersive spectroscopy device and tensile machine. The results reveal that saturated solid solution was formed in the profile at a solution temperature of 415 °C and 16 hours. During aging treatment of saturated solid solution, β-Mg₁₇Al₁₂ phase nucleates firstly at grain boundaries and takes on globular growth, which is mainly due to the lower interfacial energy in coherent or semi-coherent interface between β-Mg₁₇Al₁₂ phase and matrix phase. Lower interfacial energy is favorable to the nucleation and growth of β-Mg₁₇Al₁₂ phase at grain boundary. With the increase of aging time or the rise of aging temperature, β-Mg₁₇Al₁₂ phase precipitates out gradually from grain interior and starts to grow in globular shape. After β-Mg₁₇Al₁₂ phase grows to a certain extent, it grows in lamellar shape along the orientation of lower mismatch between β-Mg₁₇Al₁₂ phase and matrix phase. After solution at 415°C and 16h and aging at 180°C and 8h, the ultimate tensile strength and elongation to failure of the profile are 305MPa and 13%, respectively.

Abstract: SiCp/AZ61 composites reinforced with SiC particles were fabricated by semi-solid stirring-melt casting technique. The creep properties of the composites have been studied by dynamic mechanical thermal analysis, micro-structural and XRD observation. The results show that the matrix grains were refined obviously at high temperature with SiC particles introducing and the creep properties of SiCp/AZ61 composites were improved comparing with AZ61 alloy. SiC particles were substituted for Mg₁₇Al₁₂ phase that was easily intenerated at high temperature on grain boundaries. The pinning of SiC particles prevents dislocation and slip of grain boundary at high temperature.

Abstract: As abrasive water jet (AWJ) started to be used in industry, especially in aerospace and automotive industries extensively, cutting precision and accuracy has become a major requirement for further application. Unlike a knife which retains a fixed shape as it cuts through material, an AWJ stream is constantly changing. It bounces back-and-forth during cutting process. As a result, a typical surface cut by AWJ displays striation marks on the cutting surface. AWJ’s cutting front can be distinguished as a smooth upper zone and a rough lower zone. As being an energy dissipation beam cutting process, the striation marks couldn’t be eliminated completely on the cutting surface. But, by selecting proper parameters, smoother surface can be generated. However, high quality also means high cost. In manufacturing process, it is desirable to produce qualified parts with the lowest cost. This paper explored all parameters which might affect surface roughness. Based on the experimental results, an empirical model has been built and tested. With this model, predicting surface roughness becomes possible before actual cutting.

Abstract: Technological advancement, on the one hand, made Electrical Discharge Machining (EDM) much faster. One example of that is the presence of Wire Electrical Discharge Machining – High Speed (WEDM-HS) machine, which makes the material removal rate as high as 80 . On the other hand, it also made Abrasive Waterjet (AWJ) achieve much better quality surface and tighter tolerance. As a result, these two types of machining process have converged to the point where they can complement one another quite nicely in selected applications. However, it does not mean user may pick any one for their applications. The proper selection not only decreases the manufacturing costs but also achieves better quality. This paper focuses on comparing WEDM-HS with AWJ by actually cutting a special designed sample. Through comparison from several aspects which include dimension precision, surface roughness, cost, cutting time and surface damage, a proper selection guidance for regular user has been provided.

Abstract: According to spiral bevel gear machining process, use the method of computer simulation to get the discrete points’ three-dimensional coordinates of Gleason spiral bevel gear tooth surface, and then solve the tooth surfaces’ NURBS surface as the unified mathematical model. On this basis, research the curvature of tooth surfaces of various types of Gleason spiral bevel gear, draw the mean curvature diagram, and study the link between the adjustment of processing parameters and the change of tooth surfaces’ mean curvature. Establish a theoretical foundation for the processing error adjustment based on tooth surface’s curvature diagram.

Abstract: Corrosion behaviors of X80 pipeline steel were investigated in different simulated alkaline soil solution using electrochemical test, EDS coupled to SEM and weight loss method. The results showed uniform corrosion was happened on X80 steel in Shanshan and Hami simulated solution, and local corrosion was the main failure mode for X80 steel in Yumen simulated solution. The ranking of corrosion rate of X80 steel from the biggest in simulated solution was Hami, Shanshan and Yumen. With the increasing of immersion time, a dense Ca²⁺ deposited layer was formed on the surface of X80 steel, which could inhibiting the Cl^- effects on the corrosion of X80 steel in Shanshan and Hami solution. The SO₄^2- competition absorbed effect could provide certain corrosion protection for X80 steel in Yumen solution at the early corrosion stage.

Abstract: In this paper, Boron doped diamond (BDD) thin films have been deposited on Ti substrates by microwave plasma chemical vapour deposition (MWCVD). Raman spectroscopy scanning electron microscopy (SEM) and X-ray diffraction (XRD) examinations demonstrate that the electrode has well-defined diamond features. It is observed that the BDD electrode has a high overpotential 2.5V for water electrolysis prohibiting the evolution of oxygen in the cyclic voltammetry test. Further more，the removal efficiency of chemical oxygen demand (COD) is evaluated by the electrochemical oxidation of wastewater containing phenol.

Abstract: It analyzed the influence on parts’ shear surface quality by the stress and strain in the deformation area of materials. The analysis shows that the continuum linear rigid-plastic model and the fracture failure criterion in the light of damage factor, which is based on the microcosmic structure, and can accurately simulate the closed extruding fine-blanking processing; and that the higher the filling rate of outer ring is, the larger pressure stress are the deformation materials under; also that the greater the compressive stress of deformation area materials is, the higher does the deformation limit, the time of materials’ crack is delayed.

Abstract: Many balancing devices have been created to reduce machinery vibration especially in a high-speed rotor system which is very sensitive to the rotating mass unbalance. The best solution is that this device can self-perceive vibration changes and then respond these changes in an optimized way according to the different situations, which means it is a self-recovery system. According to this consideration, an electromagnetic driven bi-disc compensator for rotor auto-balancing is proposed here. In this system, rotor unbalance is online identified and calculated, after that the balancing discs will be driven to the best compensating positions, so that the unbalance can be suppressed or eliminated. Long transition time and transient vibration enhancement are terrible roadblocks which limit the industry applications of such auto-balancing system. To solve these deficiencies, a freely rotation bi-disc strategy was established and the solutions of two special cases were also discussed. A rotor auto-balancing test rig was build up. Experiments using the new solution on this rig showed that the electromagnetic compensator could be moved more accurate and effective, by which not only the balancing time was reduced, but also the transient vibration enhancement was avoided.

Abstract: The effect of Si content on structure and wear resistance of cold roll steel with 5%Cr by using vacuum arc melting furnace had been studied in this paper. Results showed that with increasing Si content martensite got coarsening and the number and content of primary carbide increased; The type of primary carbide was M7C3 and Si mainly dissolved into martensite by XRD analysis; The wear resistance was effectively improved while Si content increased. The appropriate Si content in cold roll steel with 5%Cr was 1.5%~2％.