Advanced Materials Research Vols. 146-147

Abstract: Nanoscale titanium dioxide powder were prepared in terms of sol-gel process with Ti(OC4H9) as raw material. TEM analysis show that the size of nanoparticle are between 50～ 100nm.The results of XRD test indicate that the crystal style of the product is rutile type. In order to apply nanoscale titanium dioxide to coating as pigment, the nanoscale particles were modified in terms of esterifying reaction,silane coupling agent and organic titanate coupling agent. The results of contact angle test show that the oleophilic of modified product with organic titanate coupling agent is stronger than that with silane coupling agent and esterifying reaction.

Abstract: This paper presents the comparative study on three types of fatigue data editing technique for summarising long records of fatigue data. Two of techniques were developed based on timefrequency domain (continous wavelet and discrete wavelet) and another one technique was developed based on time domain. These three techniques are used to extract fatigue damaging events in the record that cause the majority of fatigue damage, whilst preserving the load cycle sequence in the data. The objective of this study is to observe the capability of each technique in summarising long records of fatigue data. For the purpose of this study, two set of nonstationary data that exhibits random behaviour was used. This random data was measured in microstrain unit on the SAE1045 material that were used as a lower suspension arm of a car. Experimentally, the data was collected for 60 seconds at sampling rate of 500Hz, which gave 30, 000 discrete data points. The result of the study indicates that all techniques are applicable in detecting and extracts fatigue damaging events that exist in the fatigue data. However, it was found that continous wavelet can extract the data better than the other technique based the shorten signals, retention of damage and statistical parameter.

Abstract: The correlation of age hardening behavior and Si precipitation in α(Al) of Al-8wt%Si-0.35wt%Mg alloy has been investigated by micro hardness measurement, electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) analysis. The EPMA results show that Si concentration in the center of α (Al) dendrites is higher than that in the edge and the main concentration is about 1.5wt% for Al-8wt%Si-0.35wt%Mg alloy in as cast condition. After solution treatment at 530 °C for 8 h followed by water quenching (T4 treatment), hardness value decreases 9 HV, which is accompanied by the decrease of Si concentration in α (Al). Aging the as-cast sample and T4 treatment sample at 150 °C for 20 h, the main concentration of Mg and Si in α (Al) changes little. Hardness value after as-cast aging is only 3 HV lower than that after T6 treatment. Nanometer Si particles and β″ and/or β′ phases are found in aged samples. The higher hardness value for as-cast aging samples should contribute to the nanometer Si particles in α (Al).

Abstract: This research aims to investigate the pore structures and the interfacial transition zone (ITZ) of concrete containing both slag and fly ash. Test variables include three water-to-binder ratios (0.35, 0.50, 0.70) and four substitute ratios of cement with pozzolanic materials (20%, 30%, 50% and 60%). The specimens were tested to determine compressive strength, MIP porosity measurement and ITZ microhardness. Test results show that concrete containing slag and fly ash produce evident filling effect and the pozzolanic reaction after 28 days. At the age of 91 days the pozzolanic materials has provided prominent contribution to the strength, the porosity and the ITZ of concrete, making the pore volume smaller and ITZ property of pozzolanic concrete better than that of normal concrete. The concrete that adds suitable amount of pozzolanic materials (ex. 10% slag + 10% fly ash) has the optimum microstructure and mechanical property. Too much pozzolanic materials (ex. 40% slag + 20% fly ash) may be disadvantage to the concrete, and the suggested substitute ratio is under 50%. It is found that the compressive strength has the closest relationship with the total pore volume, so we use the total pore volume to predict the compressive strength of pozzolanic concrete and establish a prediction model as follow: S= -662.68Vt+87.29, R2=0.946.

Abstract: On the basis of numerous experimental results the effect of heat treatment on mechanical properties of TC4 alloy is studied. A computer model expressing the relationships between heat treatment and mechanical properties has been established with a back propagation feed forword artificial neural network method. The optimization methods based on artificial neural network and the genetic algorithm, using binary system, optimize the weight and threshold by the genetic algorithm. The calculation results show that the model has good learning precision and generalization and it can be used for predicting the mechanical properties of TC4 alloy.

Abstract: The microstructure and creep property of as-cast Mg-6Al-xNd(x=2,4,6) alloys were studied in this paper. Results showed that the needle-like Al11Nd3 phase and polygonal Al2Nd phase are the main precipitates in these alloys containing Nd, and the weight fraction of the former is much more than that of the latter. Their secondary creep rates under the applied stress of 70MPa at 175°C decreased with the content of Nd increasing and reached the minimum value of 5.0×10-8s-1 in the Mg-6Al-6Nd alloy, which is one ninth of that of the Mg-6Al alloy. The improvement in creep property of these alloys containing Nd was mainly attributed to the needle-like Al11Nd3 phase, which hindered the grain boundaries sliding and dislocation motion effectively in the creep.

Abstract: It’s very important to describe the corrosion damage evolvement rule of the aircraft structure for evaluating the calendar life. According to equivalent accelerated corrosion testing spectrum based on key environment data, the corrosion damage of accelerating corrosion testing for 7d is equivalent to that of field exposure for 1a. The new aluminum alloy of aircraft structure has been accelerated tested for 10a. Through KH-7700 3-D optical microscope, corrosion damage was inspected and measured. The result shows that some independent pits generate on the alclad surface in the first, and then many pits interconnect leading to the bigger holes. The effective service life of the aluminum alclad was gotten under equivalent accelerated corrosion testing condition.

Abstract: The kinetics of Mg2Sn synthesis reaction was studied under isothermal condition in the present paper. Results indicated that the isothermal reaction of Mg2Sn was controlled by two reactive mechanisms: the nucleation and growth control in the first stage corresponding to the Avrami exponent, m≈3, and the phase boundary control in the second stage corresponding to m≈1.1. The reactive activation energy (Ea ) for the two stages was 293.6 kJ·mol-1 and 358.1 kJ·mol-1, respectively. The microstructural evolution in Mg2Sn synthesis process was in good agreement with the two reactive mechanisms.

Abstract: Effects of Nb surface alloying and Nb-C duplex treatment alloying on corrosion behavior of TiAl in particular medium by constant potential of the three electrochemical corrosion properties, respectively, compared with the experimental base after alloying of corrosion resistance. Experimental results show that the corrosion resistance of the niobizing alloyed layer and the plasma carburized layer are increased in 3.5% NaCl,5.8% HCl,in 8.8% H2SO4 solution.

Abstract: Semi-solid magnesium alloy slurry was produced by a newly self-developed mechanical stirring machine in order to prepare continuous semi-solid slurry. The changing principle of semi-solid microstructure was studied under different conditions—the changing of temperature, stirring rate, cooling rate and stirring time. It was showed that the lower the temperature of slurry, the higher the stirring rate, the longer the stirring time and the faster the cooling rate, the grain will be smaller and more evenly rounded. When the stirring speed and temperature are the same, better semi-solid spherical grains can be gained by increasing the stirring time. At the same stirring temperature and higher stirring speed, semi-solid spherical particles are smaller, rounder and more evenly; at a low stirring speed, we can't get ideal semi-solid spherical grains even if we increase the stirring time. The ideal technological parameters of semi-solid AZ61 alloy produced with no-dendritic structure were recommended to be 600°C～605°C (stirring end temperature) 、3min～ 5min(stirring time) and 500r/min(stirring rate). Compared with conventional casting alloy, semi-solid alloy mechanical properties were greatly improved. The non-dendrite semi-solid forming mechanism was studied; mechanical stirring semi-solid non-dendritic formation was the result of a variety of factors, the key cause is mechanical shear stress.