Materials Science Forum Vol. 749

Abstract: With the thermal simulated technique, the softening mechanism in heat affected zone (HAZ) of 2519 Al-Cu Alloy is studied. The results show that over aging of the precipitates leads θ' to the softening of HAZ. With the thermal cycling peak temperature increasing, the dimension of precipitates become coarse and the amount is reduced, therefore the strength and the hardness decreased. When the peak temperature is 476, the strength and the hardness are the lowest. With the peak temperature keeps on increasing, small part precipitates continue to grow. Most of fine needle-like θ' phases dissolve and separate out renewably, which is the reason that the strength and hardness are gradually enhanced.

Abstract: The diamond films deposition experiment is carried out with MPCVD system. Some technology problems are discussed respectively, such as the substrate pretreatment, gases source compositions and deposition temperature. XRD pictures with different peaks illustrated that diamond film has good crystal orientation. A density of film crystal is observed and a thickness uniformity in detected by Scanning Electron Microscopy (SEM). The pureness of the diamond film was measured by Raman spectroscopy. The parameter coincidence rate is 90% based on the 10 prepared samples

Abstract: The effects of strain rate on the tensile deformation behavior of quenching and partitioning (Q&P) steel applied to the auto industry were investigated. The results indicated that the strength of Q&P steel raised with increasing strain rate. The variation of elongation which presented the trend of declining (10^-4 s^-1~10¹ s^-1) followed by rising to the peak (8×10¹ s^-1) then falling again (10² s^-1~10³ s^-1), is mainly caused by the transformation from retained austenite to martensite, namely the TRIP effect.

Abstract: The mechanical properties and corrosion performances of the ZL101 alloy modified by the composite master alloy were investigated. The results showed that the master alloy had not only obvious effect of grain refinement, but also a significant role in refining dendrite grain of ZL101 alloy. The grain size decreased dramatically from 150μm to 62μm when the addition of composite master alloy is up to 0.5%(mass fraction) and the temperature is 720 for 30 minutes,. Its tensile strength and elongation increased by 27% and 42% respectively. The grain refinement of ZL101 alloy decreased its corrosion performance. The morphology of Si changed into globular from needle modified by NaF, instead of AlTiB.

Abstract: Lotus-type porous structure is a new kind of micro-channel structure and can be used as heat sink for heat elimination of high powered electronic devices. Numerical analysis based on the simple fin model was used to predict the equivalent heat transfer coefficient of lotus-type porous copper micro-channel heat sink. Compared with the water, GaInSn working fluid could further promote the heat transfer performance of the heat sink. According to the theoretical analysis, a heat transfer coefficient as high as 14W/(cm²K) was attainable when the pressure drop was 50 KPa and an appropriate structure parameters: 0.4 mm in pore diameter, 0.4 in porosity and 4mm in height of porous copper were achieved.

Abstract: The serious dendritic segregation occurs in Cu-20Ni-5Sn alloy. The microstructure of Cu-20Ni-5Sn alloy as-cast is composed of white light dendrite (Cu-Ni solid solution), Sn-rich solid solution (Cu₂Ni₃Sn₃ phase) and block light precipitation (Ni₁₇Sn₃ phase). The microstructure of Cu-20Ni-5Sn alloy affected by alterative and homogenization temperature was studied. The results show that the alterative can refine the microstructures of the Cu-20Ni-5Sn alloy and reduce the segregation of Sn. The grains are quite fine with 0.9%Wt alterative in the alloy. The homogenization temperature of the Cu-20Ni-5Sn alloy decreases with increase of alterative content in the alloy. Grains enlarged with the increase of homogenization temperature, and the secondary phase distributes became more evenly. The optimization condition of homogenization treatment is at 800 in 24h.

Abstract: Cu-Al₂O₃ alloy combine both high electronic conductivity and high softening temperature. Cu-Al₂O₃ alloy was fabricated by internal oxidation and hot extrusion methods in the present investigation. Microstructure and properties of Cu-Al₂O₃ alloy was studied. The influence of preparation parameters, hot extrusion parameters and heat treatment on the properties of the alloy was investigated. The results indicated that the grain of the alloy was very small with a size between 2-10μm. Softening temperature of the Cu-0.6% Al₂O₃ alloy and Cu-1.0% Al₂O₃ alloy was 900. Cu-0.6%Al₂O₃ alloy and Cu-1.0% Al₂O₃ alloy meeting the requirements for electrode in resistance welding is the ideal substitution of the traditional electrode materials for resistance welding.

Abstract: Based on the Monte-Carlo simulation and fast Fourier transformation-micro-magnetism (FFTM) method, magnetic properties with different parameters for the 4×4 Magnetic Quantum Dot Arrays (QDA) were studied. The calculating processes show that the same calculated results can be obtained by both methods above. But the FFTM method can save much time in obtaining results, which suggest that the method be employed to study more complex systems. The calculated results indicate that there exists obvious difference in the magnetic hysteresis loops with different temperatures, which can be well explained by considering the relationship between the easy-magnetization axis and the organization anisotropy of the QDA system. Furthermore, saturation field (Hs) increases with the dipolar interaction increasing, which is attributed to the competition between dipolar energy (E_D) and Zeeman energy (E_Z). The calculated results can fit the experimental results very well. Besides, it is found that the dipolar interaction constant D has a great influence on magnetic properties.

Abstract: Large-diameter pipes used in offshore applications are commonly manufactured through the UOE process. The plate is crimped along its edges, formed into a U-shape and then pressed into an O-shape between two semicircular dies. The pipe is welded closed and then circumferentially expanded to obtain a highly circular shape. In this study, the two-dimensional finite element model of the whole processing of the UOE pipe production has been established, including large deformation and complex contact. The deformed geometries of different steps and distribution of the equivalent plastic strain and variation in load are analyzed. This research is helpful in UOE forming process design and evaluating the capability of the pipe mill.

Abstract: The kinetics of martensitic variant reorientation as well as the evolutional pathway under the continuous tensile stress in NiMnGa alloys has been investigated by using Phase field method. The simulated results revealed that the final structures and the pathway of evolutioncan be determined by the different external stress and there existed a critical stress to obtain the single variant. The related kinetics and the mechanism of the structural conversion were proposed to explain the inner physical nature. The pseudo-elasticity related to the structural conversion was also investigated. The mechanism of the motion for interfacial step associated with the nucleation and growth of one variant in another variant at the twin boundary was discussed.