Advanced Materials Research Vols. 189-193

Abstract: The aim of this work is to discuss the corrosion characteristics of plasma electrolytic oxidation (PEO) films formed on AZ31 magnesium alloys in alkaline silicate solution. The uniform and pitting corrosion resistance of the PEO films was investigated by potentiodynamic polarization tests and potentiodynamic scanning curve tests. The composition, the structure and the element contents of the films after immersed in 3.5 wt.% NaCl solution for different time were investigated by XRD、SEM and EDS. The results indicated that the corrosion occurred on AZ31 magnesium alloy and treated PEO samples during five days immersion, but the corrosion tendency of the PEO treated samples is smaller than that of AZ31 magnesium alloy.

Abstract: During casting process design, CAD/CAE technology can play important role to avoid macroscopic irregularity, internal defect and assure casting performance. Based on the casting process analysis and gating system design, the numerical simulation of gray iron butterfly valve was done by hydrodynamic software Flow-3D to obtain its optimal process scheme. According to the simulation results including flow field, temperature field and defect distribution, the merits and faults of designed schemes were investigated and then the feasible gating system was proposed. The results showed that, compared with top or intermediate casting, when adopting bottom casting, steady flow of molten metal and reasonable temperature distribution could be achieved. And workpiece defects mainly distributed in riser. The predicted results are in good agreement with practical ones.

Abstract: In order to improve both the hardness and the erosion resistance of cast aluminum alloys, nickel-diamond compound coatings were deposited on the alloys by a compound electroless plating process. The morphology, phase structure, hardness, erosion resistance and adhesion of the electroless coating were investigated. The results show that the pretreatment such as removing the silicon in the surface of the alloys, zinc dipping, alkali electroless nickel is necessary. The deposition of an electroless nickel coating without diamond prior to nickel-diamond electroless plating can improves the erosion resistance. A best nickel-diamond compound electroless plating process is found. The hardness of the nickel-diamond compound coating reaches 730 HV. Both the adhesion and erosion resistance of the compound coatings are very good.

Abstract: The mechanism that the magnetic field and the dispersant are helpful to chip removal, to improve the material removal rate (MRR) and to reduce the tool wear rate (TWR) was analyzed in detail.The corresponding experiments were conducted based on theoretical analysis. The experimental results show that adding a certain proportion of dispersant into the dielectric fluid and introducing the magnetic field for high speed small hole drilling by EDM can greatly improve the material removal rate and significantly decrease the tool wear rate.

Abstract: CeO₂-coated Polystyrene (CeO₂/PS) and SiO₂-coated Polystyrene (SiO₂/PS) composite particles were synthesized by chemical precipitation method. The as-synthesized composite particles samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), thermogravimetric analysis (TGA) and Zeta potential measurement. The oxide chemical mechanical polishing (CMP) performance of the as-papered composite particles was studied by atomic force microscope (AFM). The results indicated that CeO₂/PS composite particles had core-shell morphology and PS particles were uniformly coated by fluorite-structured CeO₂. The Strawberry-shaped SiO₂/PS composite particles were obtained, which particle size is about 200-300 nm. Surface roughness (RMS) within 5 μm×5 μm area of thermal oxide film surface after polished by CeO₂/PS and SiO2/PS composite particles was decreased to 0.227 nm and 0.222 nm, respectively.

Abstract: An environmentally friendly molybdate conversion coating based surface treatment was developed for AZ91D magnesium alloy. The EIS technique was employed to study the effects of the conversion bath composition and temperature on the corrosion protection performance of molybdate conversion coatings on AZ91D magnesium alloys. The optimum conditions under which obtained conversion coatings showed the best corrosion resistance were determined. The Nyquist results showed that the value of charge transfer resistance increased by 22.5 times for the sample treated in the optimized molybdate conversion bath.

Abstract: Fe–Al/Cr₃C₂ composite coatings produced from high-velocity flame spraying (HVFS) are Fe–Al intermetallic composite coatings with remarkable room-temperature and high-temperature properties. However, Fe–Al/Cr₃C₂ composite coatings have a Cr₃C₂ content of 50%. This causes the coatings to become porous and limits its room-temperature and high-temperature properties. In order to improve microstructure and properties of Fe–Al/Cr₃C₂ composite coatings, Fe–Al/Cr₃C₂RE, including Fe–Al/Cr₃C₂ and CeO₂, is sprayed by HVFS technology onto AISI 1020 steel. The properties including bonding strength and high-temperature corrosion-resistance of Fe–Al/Cr₃C₂RE composite coating are tested at 25°C and 650 °C. For comparison, two other materials, substrate AISI 1020 steel and Fe–Al/Cr₃C₂ composite coating, are tested under the same experimental conditions. The microstructures of the coatings are analyzed by scanning electronic microscopy (SEM), the cross-section morphology of Fe–Al/Cr₃C₂RE composite coating is analyzed by energy-dispersive spectroscopy (EDS), and the existing states of oxides are analyzed by transmission electron microscopy (TEM). The phases of the composite coating after corrosion are analyzed by X-ray diffraction (XRD). The results demonstrate that the properties of Fe–Al/Cr₃C₂RE composite coatings is better than that of either AISI 1020 steel or the Fe–Al/Cr₃C₂ composite coating. CeO₂ is a surface-active agent, and it significantly improves the microstructure and properties of Fe–Al/Cr₃C₂RE composite coating. CeO₂ improves the bonding strength of Fe–Al/Cr₃C₂RE composite coating by reducing the surface tension of droplet and enhancing its fluidity as well as wetting capacity on the surface of the substrate, decreasing the internal stress of coating.Adding CeO₂ to the coating produces Al₂O₃ and Cr₂O₃ oxide films, which protect the substrate AISI 1020 steel from corrosion more efficiently.

Abstract: The effective anisotropy constant and the saturation magnetization in nano composite Nd₂Fe₁₄B/α-Fe have been calculated by the law of approach to saturation (LATS) method. The applicability of the method has been analyzed. The calculated result shows that the LATS method is suitable for the calculation of the effective anisotropy constant and the saturation magnetization in nano composite permanent magnetic materials.

Abstract: The technologically system architecture of aircraft assembling process visualization is presented according to the development requirement of digital aircraft assembly. The key technologies is studied about the dynamic data associating form EBOM to PBOM, simulatiing and optimizing assembling process based on DELMIA, and lightening the 3D models, which are the technological foundation to implementation of building the assembly resource database, designing the assembly process planning, visualizing assembling process and informations. The visualization system for aircraft assembly simulation is developed and built based on C/S networked mode, which could be applied in aircraft assembly workshop. The system platform is industrially test taken the forward cargo door of one civil aircraft for example, it is proved that this visualization system could be applied in aircraft assembly field as guidance of assembling production, the accuracy and the efficiency of parts and components' assembly are improved distinctly.

Abstract: Multi-walled carbon nanotube (MWCNT)/Pb-Sn composite coatings and ordinary Pb-Sn alloy coatings were prepared by electrodeposition technique, respectively. The morphology images of the coatings in different growth time were observed by SEM at high and low magnifications. The results showed that composite coatings had a compacter and refiner surface than ordinary Pb-Sn alloy coatings; the addition of CNTs increased the number of crystal cores and changed the directions of crystal orientation, which resulted in a fine network structure.