Advanced Materials Research Vols. 415-417

Abstract: In this paper, the microstructure and mechanical properties of refine-grain AZ31 magnesium alloy sheets was investigated upon annealing under different temperature. Plasticity and fracture mechanism of refine-grain AZ31 magnesium alloy sheet was discussed.

Abstract: The development in the area of natural-fibre-reinforced composites has greatly increased in recent years. Using castor oil polyurethane (PU) as matrix for composites reinforced with lignin and cellulose from sugarcane straw is in tune with economical and environmental interests. The aim of this work was the thermal degradation study of castor oil-polyurethane composites reinforced with cellulose from sugarcane straw. For the obtainment of cellulose, sugarcane straw was pretreated by steam explosion, followed by a delignification with NaOH. For the production of the PU, the polyol (castor oil) to diisocyanate mass ratio was 1.5:1.0. Reinforcement of the matrix was done changing the concentration of cellulose fibres (5,10,15,20% w/w). Thermogravimetric analysis of the materials was carried out. The results obtained showed that the process of decomposition of the matrix occurs in one step, while for the composites it occurs in two steps. The addition of reinforcement in the matrix basically did not change the thermal stability of the composite.

Abstract: According to the working conditions of the nuclear power generator slot wedge and the principle of the heat treatment, CuCo2BeZr copper alloy was strengthened by a series of heating process test, finally acquired a good performance of the nuclear power slot wedge. The results show that, after the process of hot extrusion deformation of 85.5% and solution treatment at (940±10 )°C for 2h, then aging at 540 °C for 4h, the composition, microstructure, fracture morphology and tensile properties of CuCo2BeZr copper alloy, as the material of nuclear power generator, could meet the conditions of working continuously in high temperature enviroment.The research of CuCo2BeZr copper alloy provide scientific basis for analyzing the inner mechanism of the failure and predicting the working life of the nuclear power slot wedge material.

Abstract: This paper considers the vibtation problem of beam piezoelectric transducer. Traditional reasearches face difficulties in providing the analytical expression for the piezoelectric effect of the piezoelectric vibrator with a mass at its end as well as the improper model of piezoelectric vibrators which work in high-frequency band. In this paper, the nature of the current output in a large frequency range is explored. Firstly, static analysis of cantilever is conducted and the piezoelectric effect under a certain deformation were formuled. Next, the main vibration modes of the cantilever were modified so that the main modes are of orthogonality in nature and satisfy the boundary conditions. The dynamic deflection of the piezoelectric cantilever was also investigated using the modified vibration modes. Charge outputs of piezoelectric cantilever beam are also demonstrated. Finally, based on the theoretical analysis, some numerical results are given.

Abstract: The morphology of titanium boride in as-cast and as-forged Ti-45Al-8.5Nb-(W, B, Y) alloy containing 0.2at. % boron and the effect of borides on tensile and creep properties of the alloy are investigated. The results show that in as-cast alloy the morphology of boride appears mainly convoluted ribbons with some flakes and particles. With the extent of forging increases, the length of the ribbons decreases and their distribution is more uniform. The long ribbon in as-cast alloy is detrimental to tensile properties at both room temperature (RT) and high temperatures. The short ribbon in as-forged alloy is not harmful to RT tensile properties, but is harmful to tensile and creep properties at high temperatures. The harmful effect of the boride is due to the strain incompatibility of boride and matrix, which causes many cavities at boride/matrix boundaries and results in ultimate fracture.

Abstract: To study the ignition-proof behavior in the spray deposited magnesium alloy with nitrogen as atomizing gas, SEM and XRD were employed to study the morphology and elements profile of nitride film formed on the Mg-5Ca alloy melt in different conditions, and the ignition proof principle was also analyzed preliminarily. The results indicated that under ordinary nitrogen (99.5%), a layer of smooth and continuous nitride film was formed on the surface of Mg-5Ca alloy after sintered at 740°C for 2 hours, and with the increasing of temperature and holding time, small cracks and cavities appeared locally on the surface film. The surface film was mainly composed of CaO、MgO、Ca₃N₂ and Mg₃N₂.The profile analysis of the nitride film indicated that Ca element collected on the surface of the nitride film, and a multiple film was formed which filled the loose and holes of single film, avoided the burning of Mg alloy during spray forming process.

Abstract: The coincidence Doppler broadening spectra of single crystals of Si, Al, polycrystals of Ti, Nb and Sn, and TiAl-based alloys (TiAl, Ti₅₀Al₄₈Nb₂ and Ti₅₀Al₄₈Sn₂) have been measured and analyzed. It has been found that the 3d electron signal for binary TiAl alloy is lower than expected due to the Ti 3d-Al 3p interactions. The addition of Nb atoms to TiAl alloy leads to the enhancement of d-d interactions and thus the d electron signal in the spectrum. The d electron signal in the spectrum of Ti₅₀Al₄₈Nb₂ alloy is higher than that of Ti₅₀Al₄₈Sn₂ alloy. The influence of Nb and Sn on d electrons of TiAl alloys has been discussed.

Abstract: The main focus of this work was to study the microstructural evolution during the sintering and the heat treatment processes. The results indicated that mechanical alloying had induced the formation of supersaturated solid solution in immiscible Co-Al-W alloys, originating mainly from extensive grain boundary region, high dislocation density, and ample point defect. Spinodal decomposition is found to be the dominant mechanism for phase formation. The extremely fine grains (0.5~3 μm) provide short-circuited diffusion paths for the atomic movement that leads to the spinodal decomposition behavior. γ´ precipitates were formed by the combination of spinodal decomposition mechanism and the chemical reaction between the decomposed products of CoAl and Co₃W.

Abstract: Aluminium alloys generally has low weldability by traditional fusion welding process. The development of the Friction Stir Welding (FSW) has provided an alternative improved way of producing aluminium joints, in a faster and reliable manner. FSW process has several advantages, in particular the possibility to weld dissimilar aluminium alloys. This study focuses on the behavior of tensile strength of dissimilar joints of AA6351-T6 alloy to AA5083-H111 alloy produced by friction stir welding was analysed. Five different tool pin profile such as Straight Square (SS), Tapered Square (TS), Straight Hexagon (SH), Straight Octagon (SO) and Tapered Octagon (TO) with three different axial force (1tonne, 1.5tonne, 2 tonne) have been used to weld the joints. The effect of pin profiles and axial force on tensile properties and material flow behaviour of the joint was analyzed and it was found that the straight square pin profile with 1.5 tonne produced better tensile strength then other tool pin profile and axial force.

Abstract: The hot deformation characteristics of Al-12.7Si-0.7Mg alloy were investigated on an Instron5500 electronic universal testing machine at strain rates ranging from 1.67×10^-4 s^-1 to 1.67×10^-3 s^-1 and testing temperatures ranging from 460 °C to 520 °C. The results show that strain rate had a great effect on the flow stress. The flow stress increased with increasing the strain rate. The true stress-strain curves of the Al-12.7Si-0.7Mg alloy were obtained, and the strain rate sensitivity and hot deformation parameters of deformation activation energy were calculated. The hot deformation constitutive equation with hyperbolic sine form was also obtained. The test calculations demonstrate that the constitutive equation describes the deformation features of the Al-12.7Si-0.7Mg alloy well.