Grain refinement of pure Al with different electric current pulse modes

A comparative study on grain refinement of pure Al by applying electric current pulse (ECP) at different positions in the mould was carried out. The experimental results showed that fine equiaxed grains were generated by exerting ECP at different electrode positions, and the highest proportion of fine equiaxed grain area was obtained when ECP was applied at the upper and lower lateral wall of the mould. The refinement mechanism of exerting ECP and the reasons of different refining efficiency with various ECP employing modes were also discussed.     

In situ generation of hydrogen from water by aluminum corrosion in solutions of sodium aluminate

A new process to obtain hydrogen from water using aluminum in sodium aluminate solutions is described and compared with results obtained in aqueous sodium hydroxide. This process consumes only water and aluminum, which are raw materials much cheaper than other compounds used for in situ hydrogen generation, such as hydrocarbons and chemical hydrides, respectively. As a consequence, our process could be an economically feasible alternative for hydrogen to supply fuel cells. Results showed an improvement of the maximum rates and yields of hydrogen production when NaAlO₂ was used instead of NaOH in aqueous solutions. Yields of 100% have been reached using NaAlO₂ concentrations higher than 0.65 M and first order kinetics at concentrations below 0.75 M has been confirmed. Two different heterogeneous kinetic models are verified for NaAlO₂ aqueous solutions. The activation energy (E_a) of the process with NaAlO₂ is 71 kJ mol⁻¹, confirming a control by a chemical step. A mechanism unifying the behavior of Al corrosion in NaOH and NaAlO₂ solutions is presented. The application of this process could reduce costs in power sources based on fuel cells that nowadays use hydrides as raw material for hydrogen production.     

艾默生TD3300变频器在铝箔制造业中的改造

本文介绍了艾默生TD3300变频器在大连黄海铝加工厂铝箔生产线上的应用情况，采用张力开环控制方式，系统的构成等，重点介绍了铝箔生产线张力开环控制系统的调试过程，所遇到的问题及解决的方法。     

Atmospheric plasma deposition of glass coatings on aluminum

The deposition and properties of glass coatings on aluminum was investigated using atmospheric pressure plasma-enhanced chemical vapor deposition. The plasma, generated with radio frequency power at 27.12 MHz, was fed helium, oxygen and two types of silicon precursors, hexamethyldisilazane and tetraethylorthosilicate. After deposition, the coatings were analyzed for composition, adhesion and dielectric strength. X-ray photoelectron spectroscopy revealed that the glass coatings contained approximately 25% silicon, 50% oxygen and 25% carbon. Scratch tests indicated that the coatings were strongly adherent to the substrates. The glass coatings achieved DC dielectric strengths in between 50 and 250 V for a thickness range of 0.5 to 1.3 μm. The maximum breakdown voltage measured was 400 V. Scanning electron microscopy revealed that breakdown occurred at cracks and other defects in the coatings. These defects appeared to form around areas of surface roughness and contamination.     

Characterization of Non-Alloyed Ohmic Contacts to Si-Implanted AlGaN/GaN Heterostructures for High-Electron Mobility Transistors

This paper reports results of a study of non-alloyed ohmic contacts on Si-implanted AlGaN/GaN heterostructures, obtained from current–voltage characteristics of transfer-length method (TLM) test structures. It is shown that the measured contact resistance from the Ti/Au/Ni metal contacts, deposited on Si-implanted regions, to the two-dimensional electron gas channel at the AlGaN/GaN heterointerface of the non-implanted region, is formed by three different components: (i) contact resistance between the metal␣and the semiconductor (0.60 ± 0.16 Ω mm), (ii) resistance of the implanted region (0.62 ± 0.03 Ω mm) and (iii) an additional resistance (0.72 ± 0.24 Ω mm) giving a total value of 1.9 ± 0.3 Ω mm. The specific ohmic contact resistance was determined to be (2.4 ± 0.5) × 10⁻⁵ Ω cm².     

Characterization of semi-solid slurry using a novel “Rheo-Characterizer” apparatus

The rheological properties of A357 semi-solid slurries, produced under different conditions using the SEED process, were analyzed with a novel “Rheo-Characterizer” apparatus. The TiB₂ grain refiner was also added to evaluate the impact on the microstructure and the cutting force. The α-Al particles and grain size were measured under different processing conditions. The effect of the solid fraction on the resulting cutting force curve was also investigated by altering the cutting temperature. The results show that the “Rheo-Characterizer” is capable of differentiating between the microstructural morphologies and the solid fraction present in the slug. A simple theoretical model was proposed to better understand the relationship between the microstructure and the cutting behaviour of the semi-solid slurry. The model, together with an analysis of the deformation phenomena observed on the wire and the slug, roughly predicts the principal characteristics of the experimental cutting curves.     

深冷处理对Al2O3陶瓷颗粒纤维增强铝基复合材料的影响

采用预制件挤压铸造制备出Al2O3颗粒纤维双相增强Al基复合材料，采用X衍射仪和扫描电镜研究深冷处理对其显微组织及性能的影响。结果表明：复合材料经深冷处理后虽然硬度下降，但其抗拉强度提高，并表现出某些脆性断裂的特征。这与深冷处理前后Si相的变化有关。     

Co-deposition of Al-Cr-Ni alloys using constant potential and potential pulse techniques in AlCl3-NaCl-KCl molten salt

To improve the oxidation resistance of TiAl intermetallic compound under high temperature condition, cathodic co-deposition of Al-Cr and Al-Ni alloy was carried out by constant potential control or potential pulse control in AlCl₃-NaCl-KCl molten salt containing CrCl₂ and/or NiCl₂ at 423 K. Cathodic reduction of Ni and Cr starts at potential of 0.8 and 0.15 V versus Al/Al³⁺ in the molten salt, respectively. The co-deposition of Al, Cr, and Ni occurred at potentials more negative than −0.1 V to form a mixture of intermetallic compounds of Cr₂Al, Ni₃Al, and Al₃Ni. Concentration of Cr in the deposit was enhanced to 43 at% at −0.1 V; however, concentration of Ni in the deposit was 6 at% at the same potential. The concentration of Ni further decreased with more negative potential to 1 at% at −0.4 V. The potential pulse technique enhanced the Ni concentration in the deposit to about 30 at%, due to anodic dissolution of Al content from the deposit at the higher side of potential on the potential pulse electrolysis.     

Process map for plasma sprayed aluminum oxide-carbon nanotube nanocomposite coatings

Process map has been developed for plasma sprayed aluminum oxide (Al₂O₃) ceramic nanocomposite coatings with carbon nanotube (CNT) reinforcement in varying content and spatial distribution. The process map was constructed using the temperature and velocity data of the in-flight powder particles exiting from the plasma plume. Process map elucidates the interdependence of powder feedstock pre-treatment, CNT content and dispersion behavior on the in-flight particle thermal history and subsequently evolving microstructure and coating properties. High thermal conductivity of CNTs alters the heat transfer characteristic during the splat formation. Microstructure of the coatings consists of fully melted zone (FM), partially melted or solid-state sintered zone (PM) and porosity. Process map provides a processing control tool for plasma spraying of Al₂O₃-CNT nanocomposite coatings.