Advanced Materials Research Vols. 335-336

Abstract: Sr added ignition-proof AZ91D-0.3Be magnesium alloy was prepared. The influence of Sr content on microstructure and mechanical properties of the alloy was studied. Results show that the microstructure of ignition-proof AZ91D-0.3Be magnesium alloy is refined by a small amount of Sr addition. It is due to that the enrichment of a few Sr atoms in solid liquid interface in the process of magnesium alloy solidification inhibits grain growth and accelerates more nucleation. However, with increasing of Sr addition the microstructure is coarsened. By 0.01% Sr addition the tensile strength of as-cast experimental alloy is increased by about 25% and that of both the solid-solution and aged alloy is increased by about 40%. The elongation of as-cast alloy is increased by about 20% and that of solid-solution alloy increased by about 30%.

Abstract: Monodisperse de-ionized water droplets 4.5 μm in diameter have been produced in ultrasonic atomization using micro electro-mechanical system (MEMS)-based three-Fourier horn 1 MHz silicon nozzles. The required electrical drive power and voltage are 15 mW and 6.5 V, respectively. The nozzles measure 1.80 x 0.21 x 0.11 cm³ and can accommodate flow rate of 2 to 300 μl/min. As liquid enters the 200 μm x 200 μm central channel of the nozzle, a curved thin liquid film is maintained at the nozzle tip that vibrates longitudinally at the nozzle resonance frequency, resulting in formation of standing capillary waves on the free surface of the liquid film. As the tip vibration amplitude exceeds a threshold (critical or onset amplitude), the standing capillary waves become unstable (temporal instability) and a spray of monodisperse droplets (mist) is produced. The experimental results of resonance frequency, droplet diameter, voltage requirement and critical or onset amplitude support the predictions of the three-dimensional finite element simulation and the linear theory of capillary wave atomization mechanism.

Abstract: In the present study, porous titanium alloys were fabricated successfully by mixing titanium, niobium, and zirconium powder with pore-forming agent of ammonium bicarbonate via conventional sintering method. The pore characteristics, such as pore morphology and distribution, mean pore size and porosity of prepared porous TiNb₂₄Zr₄ alloy were investigated by optical microscopy, image processing and density determination. It was found that the pore characteristics mainly depended on the shape and size of used ammonium bicarbonate particles in present study. The porosity of the alloys could be tailored by controlling the amount of ammonium bicarbonate addition. The porous TiNb₂₄Zr₄ alloys were near β type titanium alloys, which consisted mainly of β phase and a little of α phase. The amount of α phase increased in the porous alloys due to segregation caused by the addition of pore-forming agent.

Abstract: The mechanical properties of a 7A04 aluminum alloy were improved by deformation strengthening and phase transformations strengthening adopting thermomechanical treatment, whose process include solution treatment, deformation treatment and ageing treatment in turn. The paper focuses on the influences of deforming degree and ageing process on microstructure and properties of 7A04 aluminum alloy. The experimental results show that hardness increased with increasing deformation ratio, and the value are greatly higher than that of samples after solution treatment. The results of ageing after deformation show that the hardness enhanced with prolonging the ageing time, which reach the peak value at 16 hours. In addition, the microstructure became more homogeneous and the grain was refined obviously by metallography microscope observation. The second phase precipitate dispersedly to strengthen the alloy. Above all, in order to obtain the better mechanical properties, the optimal thermomechanical treatment processes are solution treatment at 470°C for 2h, deformation with ratio of 40% as well as ageing at 120°C for 16h.

Abstract: This paper intends to get compressive loading effect on fatigue crack growth of 2A12 aluminum alloy. The fatigue crack propagation tests at negative stress ratio R=-0.5, -1and -2 were made in different applied compressive loading. The result showed that the effect of the compressive loading part of the applied stress cycle on fatigue crack growth rate in 2A12 aluminum alloy at negative stress ratio can not be omitted.

Abstract: The purpose of this study is to investigate the optimal process parameters use to fabricated a standardized cranial implant using deep drawing with a titanium mesh sheet. First, the mold for deep drawing, consisting of die, punch, blankholder and blank sheet, was designed within a CAD program. Then the formability of the mold was simulated using FE software. Furthermore, a link between the result of the FE simulation and CAE program was established to determine the best input parameters in the deep drawing system which produced minimal defects (wrinkles and ruptures). The parameters of interest in this study were the overall friction coefficient, blankholder friction coefficient, blankholder force and blank sheet thickness. The results showed the high feasibility of the joint CAE program and optimization procedure to calculate the best input parameters which can reduce time and cost consuming physical tryouts.

Abstract: Conventional extrusion and artificial aging were combined to investigate the possibility of superposing precipitation strengthening on texture strengthening. Uniaxial tension test was used to characterize the mechanical properties and the static toughness values were calculated. Metallographic microscope and TEM were employed to observe the microstructures after extrusion and artificial aging. It is shown that remarkable discontinuous precipitation occurs after artificial aging at 150 °C. Although static toughness was slightly reduced, the yield strength was obviously increased and therefore good strengthening and toughening effect was achieved.

Abstract: Comprehensive performance of 6061 aluminum alloy was improved by solution treatment and two-step ageing treatment in this paper . The effects of different thermal processing parameters on the microstructure and mechanical properties of 6061 aluminum alloy were studied. The experimental results show that the optimal process of solution treatment for 6061 aluminum alloy is heated at 500°C for 10min. After first-stage aging, the hardness measurements and microstructure analysis results show that the hardness increased with increasing aging temperature, and reached peak value at temperature 180°C for 10h, while in the second-stage ageing treatment, the sample got the ageing peak value at 220°C for 1h. After two-stage treatment, the grains of 6061 aluminum alloy became uniform and fine and the second phase distributed along the grain boundary and play an important role of dispersion strengthening. Above all, the optimal heat treatment process of 6061 aluminum alloy is solution treated at 500°C for 10min, as well as ageing at 180°C, 10h and 220°C, 1h

Abstract: Abstract: The microscopic structure of Pb-Ca alloys and Pb-Ca-Sn_X-Al alloys was observed by scanning electron microscope (SEM). The high temperature effect on corrosion behaviors and anode film Pb(Ⅱ) of Pb-Ca alloys and Pb-Ca-Sn_X-Al alloys was studied using linear sweep voltammetry, electrochemical impedance spectra (EIS) and AC voltammetry. It was found that the oxidation tendency of t-PbO to nonstoichiometric oxide PbOx and PbSO₄ to ß-PbO₂ may be increased at high temperature. With the increase of tin content, total corrosion and harm of corrosion can be reduced, the resistance of anode film decreased and the ions motion tendency enhanced.

Abstract: The effect of different aluminum content on peritectic reaction and mechanical properties of pentatomic TiAl-based alloy was investigated. The results indicate that the grain size gradually increase with increasing content of aluminum and addition 45.7% aluminum in TiAl-based alloy results in that the peritectic reaction can increase grain size greatly, respectively. The content of aluminum can increase the room temperature strength, high temperature strength but peritectic reaction can effectively reduce tensile strength. Aluminum content has a little effect on the ductility. The stress rupture life has positive correlation relationship with the content of aluminum.