Effect of Structural Parameters on the Thermal Stress of a NiFe2O4-Based Cermet Inert Anode in Aluminum Electrolysis

Inert anode has been a hot issue in the aluminum industry for many decades. With the help of FEA(finite element analysis) software ANSYS,a model was developed to simulate the thermal stress distribution working condition of an inert anode. To reduce its thermal stress,the effect of some parameters on the thermal stress distribution was investigated,including the anode height,the anode radius,the hole depth,the hole radius,and the radius of inner chamfer and outer chamfer. The results showed that in the actual working condition of an inert anode,there existed a large axial tensile stress near the tangent interface between the anode and bath,which was the major cause of anode breaking. Increasing the anode height and reducing the hole depth properly seemed to be beneficial for the stress distribution. With the increase of anode radius,the stress distribution became better first and then deteriorated,the reasonable value was between 0.045 to 0.06m. The hole radius had a significant effect on the stress and a smaller radius would reduce the thermal stress. The effect of the radius of the inner chamfer and the outer chamfer was less than other parameters.     

METAL INERT GAS WELDING OF 2519-T87 HIGH STRENGTH ALUMINUM ALLOY

20 mm thick plates of 2519-T87 high strength aluminum alloy have been welded.The effects of the compositions of filler wires,the heat input and the compositions of shielding gas on the mechanical properties and microstructure of the welded joint have been investigated.The results indicate that finer microstructure,better mechanical properties and higher value of hardness of HAZ can be obtained by using lower heat input.The use of Ar/He mixed shielding gas has several advan- tages over pure Ar shielding gas.With the increase of the proportion of He in the mixed shielding gas, the grain size of the weld metal as well as porosity susceptibility decreases.When the volume ratio of He to Ar reaches 7:3,the porosity and the grain size of weld metal reach the minimum,and the po- rosity can be further reduced by filling some CO_2.     

Stress Generated on Aluminum During Anodization as a Function of Current Density and pH

Anodic oxidation is accompanied by stressgeneration during the growth of the oxide. The presentstudy focuses on the stress-generation mechanism onaluminum as a function of the applied current density in acidic solutions of sulfuric acid ofdifferent strengths giving variable pH. Abeam-deflection technique was utilized for thedetermination of the magnitude and direction of stressesgenerated during the anodic oxidation process. Generally,thickness of the oxide determines whether the stress iscompressive or tensile in nature. The results have beeninterpreted in terms of the formation and annihilation of anion (O^2-) and cation(Al³⁺) vacancies. A reduction in thealuminum-ion vacancy concentration (V Al ³ ) results in a compressive stressdeflection, whereas tensile-stress deflection isintroduced by an increase in the oxygen vacancy(Vo²⁺) concentration. The mechanism isfurther elucidated by current-density jump/dropexperiments. The results show that stress in this caseis affected by the dissolution of the oxide at the oxide-electrolyteinterface.     

Effect of interfacial weight loss by silver migration on the pullout strength of a silver wire embedded in an adhesive matrix

In this study an effort is made to correlate interfacial weight loss, by migration, from the surface of a silver wire embedded in an adhesive matrix, to bond strength between the silver wire and the adhesive matrix. Comparative studies are also performed using an aluminum an wire in place of silver to accurately assess the effect of interfacial weight loss by silver migration. The results of the pullout tests on silver migrated specimens are compared with pullout tests on silver-wire specimens, which were immersed in water for 2 h but without silver migration. Pullout tests are performed in both wet, and dry conditions of the bonded specimens. It is determined that the pullout strength of bonded silver-wire specimens in wet condition decreases by as much as 86%, subsequent to silver migration. The loss of bond strength for silver-migrated specimens tested in dry condition varies between 23% and 4%, depending on the embedded length used.     

Evidence for formation of metallo-siloxane bonds by comparison of dip-coated and electrodeposited silane films

It has been amply demonstrated that thin films of organofunctional silanes deposited by dipping or spraying on metals, such as aluminum, can provide protection against various forms of corrosion. In this paper we show that denser films with higher pore resistance and better corrosion protection performance can be obtained if the silane film is produced by electrodeposition rather than by dipping. In such a process the silane reacts with the metal oxide in a different way, and in the case of aluminum, aluminate ions seem to be incorporated into the silane film. The resulting films can protect aluminum alloys against uniform and pitting forms of corrosion in a salt solution for more than 1000 h, which is comparable to the standard chromate-based treatments. This paper discusses the protection mechanism in some detail. An important aspect of this work is that the use of XPS and TOFSIMS to analyze electrodeposited silane films provided direct evidence for the presence of O₂Al(O–Si–O) and OAl(O–Si–O)₂ groups at the silane–aluminum oxide interface. Such bonds have been suggested, but they have largely remained elusive over the years.     

Silanization of adhesively bonded aluminum alloy AA6060 with γ-glycidoxypropyltrimethoxysilane. II. Stability in degrading environments

Alkaline etched aluminum alloy AA6060 treated with of γ-glycidoxypropyltrimethoxysilane was investigated. The stability of the silane films in degrading environments was investigated by exposing them to acidic and alkaline solutions at 40°C, followed by analysis with reflection-absorption infrared spectroscopy. Desorption of the silane from the surface occurred at pH 4, and at a much slower rate at pH 7, while the silane film was stable at pH 8. Two models for the degradation of the silanized aluminum surface in an acidic environment were proposed: one involving simultaneously hydrolysis of the siloxane network and corrosion of the underlying aluminum surface, and the other involving only corrosion of the aluminum surface. The durability of the silane treated surface was determined using wedge tests on joints made with XD4600 one-component epoxy adhesive. The durability was significantly reduced in highly acidic environment (pH 2), but no significant differences in durability were observed in the pH range from 4 to 11, except that the durability was slightly higher in higher alkaline environment during the initial period of testing. Better durability in an alkaline environment is connected to a better stability of both the siloxane network and the aluminum surface in this environment.     

Influence of tin addition on corrosion resistance of aluminium ion platings

Abstract

Aluminium ion platings are galvanically compatible with the aluminium alloys used in the aircraft industry and prevent galvanic attack when in contact with them. However, these platings fail to provide the good lubricity which the traditional, but toxic, cadmium platings are known to provide. Adding tin to aluminium ion platings can improve their frictional characteristics. In this work, electrochemical polarisation and metallurgical studies have been used to examine the influence qf introducing 5%Sn into aluminium ion platings on their corrosion resistance. Results have shown an increase in the corrosion tendency as indicated by a shift of the corrosion potential in the active direction and an increase in the corrosion current density which can be related to a galvanic action between two different phases of aluminium rich columnar grains. Domes observed within these grains can easily be removed during early stages of corrosion leaving cavities in the platings, thus providing another possibility of galvanic attack between the plating and substrate taking place.     

Prevention of Ice Accretion on Aluminum Surfaces by Enhancing Their Hydrophobic Properties

The accretion of ice on the surfaces of power network systems, aircraft, communication networks, etc., is known to cause serious problems that often lead to costly safety issues. An ideal solution would be to prevent ice from accumulating in the first place, rather than waiting for ice to accrete and then to de-ice which is both time-consuming and expensive. This may be accomplished by depositing coating materials that are icephobic. A low dielectric constant surface is expected to reduce the adhesion of ice due to the screening of mirror charges, thereby eliminating one of the strongest interaction forces — the electrostatic force of attraction — at the ice–surface interface. Superhydrophobic surfaces, which demonstrate high water-repellency due to the negligible contact area of water with these surfaces, are also expected to minimize the contact area of ice. In the present research work, both concepts were studied by producing superhydrophobic nanorough low-ε (dielectric) surfaces on aluminum. Superhydrophobic properties were achieved on surfaces of aluminum by creating a certain nanoroughness using a chemical etch followed by 'passivation' of the surface by a low surface energy coating of rf-sputtered Teflon, providing a water contact angle greater than 160°. The same behavior is reported even when the nanorough substrates were coated with dielectric thin films of ZnO (lower ε) or TiO 2 (higher ε) prior to passivation. It is found that the superhydrophobic nanorough low energy surfaces are also icephobic and the presence of a low dielectric constant surface coating of Teflon (ε = 2) allows a considerable reduction of the ice adhesion strength. Ice adhesion strengths were determined using a centrifugal ice adhesion test apparatus.     

Modeling and Experimental Research of Four-Strand Low-Frequency Electromagnetic Casting Aluminum Alloy

With the aid of ANSYS software, the effect of different mould external part materials on magnetic flux density in the aluminum melt and magnetic field interaction of four coils applied with same currents were investigated. Calculating results showed that magnetic flux density in the aluminum melt was greatly improved and the magnetic field interaction among different coils was decreased when external part of mould is made of soft magnetic material. Based on the finding, a four-strand low-frequency electromagnetic casting 6063 aluminum alloy experiment was carried out in the laboratory. The experiment showed that the surface of the billet was smooth and had no exudations and cold shuts, the as-cast microstructures were fine, uniform, equiaxed, net-globular or globular under low-frequency electromagnetic field. The microstructure becomes finer with increased current value.     

Surface Modification of Polymer Films for Improved Adhesion of Deposited Metal Layers

Plasma treatment and vacuum Al deposition on films from biaxially oriented polypropylene is a multistep large scale industrial process, mainly ending up in packaging film laminates. As atmospheric plasma treatment processes suffer from lack of reproducibility, low pressure plasma treatment processes that can be operated in-line with the metal deposition are being developed. Process development is difficult, because the final packaging film laminate has to deliver optimum properties of adhesion as well as of the barrier against oxygen and water vapor permeation. As a typical production run involves tens of thousands to up to one hundred thousand square meters of film, experiments on an industrial scale are expensive, so smaller scale experimental processes are needed, which so far do not match well enough with industrial process characteristics. Moreover, bonding mechanisms between the treated substrate film and the deposited Al layer are not sufficiently understood. This paper describes the sequence in development and optimization of substrate films and plasma treatment that has been performed on an experimental as well as on an industrial scale. A sufficient correlation between experimental and industrial scales was achieved, which helps to perform development and optimization on a small scale before scaling up to industrial processes. However, improvement is still needed both in fundamental understanding of the aluminum–polypropylene interface as well as in experimental equipment and methodology.