Film formation in trihexyl(tetradecyl)phosphonium diphenylphosphate ([P6,6,6,14][dpp]) ionic liquid on AA5083 aluminium alloy

Whilst ionic liquids (IL) have been shown to inhibit corrosion on some reactive metals and alloys by forming a surface film, e.g. Li and Mg, understanding of the interaction between ionic liquids and aluminium is lacking. This research study investigated the viability of film formation on AA5083 Aluminium Alloy by electrochemical treatments in the trihexyl(tetradecyl)phosphonium diphenylphosphate ([P6,6,6,14][dpp]) IL. Two-step anodic treatments were performed on AA5083 in the IL, followed by a comparison of the corrosion behaviour of the IL-treated samples with that of a control. It has been revealed that the two-step IL-treatment led to reduced current densities on AA5083 under cyclic voltammetry scan in the IL before and after the IL-treatment. Lower corrosion rates have been shown on all samples treated in IL at room temperature. Surface characterisation showed a non-uniform porous film on the 50°C IL-treated sample with a film thickness ranging between 37nm and 155nm. The IL-film enhanced the corrosion resistance of AA5083 by protecting the Al-matrix and Fe-rich intermetallic particles (IMPs). Although findings of this study suggest similar IL-film formation as that on Li and Mg, more research needs to be conducted to optimise the electrochemical treatment conditions and ultimately to develop a robust IL-film formation procedure for corrosion protection.

Electrochemical and DFT studies of quinoline derivatives on corrosion inhibition of AA5052 aluminium alloy in NaCl solution

Two quinoline derivatives, 8-aminoquinoline (8-AQ) and 8-nitroquinoline (8-NQ), have been used as inhibitors to examine their corrosion protection effect on AA5052 aluminium alloy in 3% NaCl solution. The weight-loss and electrochemical measurement have indicated that 8-AQ and 8-NQ play as anodic inhibitor to retard the anodic electrochemical process. SEM/EDS analysis clearly shows that 8-AQ and 8-NQ form a protective film on the AA5052 alloy surface. Density functional theory (DFT) calculation confirmed the formation of strong hybridization between the p-orbital of reactive sites in the inhibitor molecules and the sp-orbital of the Al atom. 8-aminoquinoline and 8-nitroquinoline may be useful as effective corrosion inhibitors for aluminium alloys.

Experimental and theoretical investigation on corrosion inhibition of AA5052 aluminium alloy by l-cysteine in alkaline solution

The corrosion inhibition of l-cysteine on AA5052 aluminium alloy in 4 mol/L NaOH solution was investigated by hydrogen gas evolution experiment, polarisation curve, galvanostatic discharge, electrochemical impedance spectroscopy measurements and quantum chemical calculations. The adsorption of l-cysteine on aluminium alloy surface obeyed the amended Langmuir's adsorption isotherm. The polarisation curves indicated that l-cysteine acted as a cathodic inhibitor to inhibit cathodic reaction. The inhibition mechanism was dominated by the geometric covering effect. The galvanostatic discharge shows that the additives restrain the hydrogen evolution and increase the anodic utilization rate. Quantum chemical calculations indicated that l-cysteine molecules mainly interacted with on the carboxyl groups on the aluminium alloy surface. A strong hybridization occurred between the s-orbital and p-orbital of reactive sites in the l-cysteine molecule and the sp-orbital of Aluminium.

The generation of new high-angle boundaries in aluminium during hot torsion

The crystallographic rotation field for deformation in torsion is such that it is possible for orientations close to stable orientations to rotate away from the stable orientation. A Taylor type model was used to demonstrate that this phenomenon has the potential to transform randomly generated low-angle boundaries into high-angle boundaries. After imposing an equivalent strain of 1.2, up to 40% of the simulated boundaries displayed a disorientation in excess of 15°. These high-angle boundaries were characterised by a disorientation axis close to parallel with the sample radial direction. A series of hot torsion tests was carried out on 1050 aluminium to seek evidence for boundaries formed by this mechanism. A number of deformation-induced high-angle boundaries were identified. Many of these boundaries showed disorientation axes and rotation senses similar to those seen in the simulations. Between 10% and 25% of all the high-angle boundary present in samples twisted to equivalent strains between 2 and 7 could be attributed to the present mechanism.

Method for determining reaction rate of mild steel containers during melting of magnesium-aluminium alloys and effect of aluminium content on directionally solidified microstructures

A magnesium alloy of eutectic composition (33 wt-'%Al) was directionally solidified in mild steel tubes at two growth rates, 32 and 580 mum s(-1,) in a temperature gradient between 10 and 20 K mm(-1). After directional solidification, the composition of each specimen varied dramatically, from 32'%Al in the region that had remained solid to 18%Al (32 mum s(-1) specimen) and 13%Al (580 mum s(-1) specimen) at the plane that had been quenched from the eutectic temperature. As the aluminium content decreased, the microstructure contained an increasing volume fraction of primary magnesium dendrites and the eutectic morphology gradually changed from lamellar to partially divorced. The reduction in aluminium content was caused by the growth of an Al-Fe phase ahead of the Mg-Al growth front. Most of the growth of the Al-Fe phase occurred during the remelting period before directional solidification. The thickness of the Al-Fe phase increased with increased temperature and time of contact with the molten Mg-Al alloy. (C) 2003 Maney Publishing.

A nitrocarburising and low-temperature chromising duplex surface treatment

A duplex surface treatment has been developed involving the pre-treatment of hardened and tempered AISI H13 chromium hot-work tool steel by a ferritic nitrocarburising process, and a subsequent treatment of the nitrocarburised surface by a low-temperature chromium thermo-reactive deposition process.  The process formed a thin and hard chromium carbonitride surface layer above a hardened diffusion zone, and the low processing temperature allowed the properties of the core material to be retained. It is expected this surface treatment will find application in the treatment  of tooling used for aluminium forming operations.

Surface analysis of aluminium by glow-discharge optical emission spectrometry

Surface engineering in solids has become an important field in materials science. Glow-discharge optical emission spectrometry (GD-OES) has proven to be a powerful tool for the rapid analysis of elements in the surface of solids. One may employ GD-OES to determine quantitatively the bulk concentration of elements in a sample, and elemental concentrations as a function of depth. Presented here is an overview of GD-OES analysis and an application to aluminium.

Stress analysis of compression of aluminium with rotating tools

Compression tests carried out on aluminium specimens showed that when the die was rotated the compression load dropped. A slab method is employed to examine this process. The load reduction is explained by the deviation of friction vector due to the relative circumferential movement between the die and the material. This mechanism is incorporated into a theoretical model and an expression is derived for compression pressure. Analytical solutions established compare favourably with experimental results. It is also shown that there is a limitation to the load reduction: the compressive load can never be lower than 70 percent of the yield limit.

Machine vision system for automatic inspection of surface defects in aluminium die casting

A machine vision system is presented for the automatic inspection of surface defects in aluminium die casting. The system uses a hybrid image processing algorithm based on mathematic morphology to detect defects with different sizes and shapes. The defect inspection algorithm consists of two parts. One is a parameter learning algorithm, in which a genetic algorithm is used to extract optimal structuring element parameters, and segmentation and noise removal thresholds. The second part is a defect detection algorithm, in which the parameters obtained by a genetic algorithm are used for morphological operations. The machine vision system has been applied in an industrial setting to detect two types of casting defects: parts mix-up and any defects on the surface of castings. The system performs with a 99% or higher accuracy for both part mix-up and defect detection and is currently used in industry as part of normal production.

Crushing simulation of foam-filled aluminium tubes

A numerical study is presented in this paper to investigate the energy absorption of foam-filled aluminium tubes during crushing. The post-buckling mode of the foam-tube structures has been successfully simulated. The predicted compressive load-displacement is in a good agreement with experimental results. The energy absorption ability of the composite structure due to plastic deformation in a crushing process is evaluated by comparison with the tube structure without foam. The results indicate that the energy absorption of a foam-filled tube structure is superior to the tube without foam. The influences of the friction and the geometric parameters of the structure on the energy absorption have also been investigated. Results from this study will assist automotive industry to design crashworthy components based on foam-filled tubes.

The effect of laser power density on the fatigue life of laser-shock-peened 7050 aluminium alloy

Laser shock peening (LSP) is an innovative surface treatment method that can result in significant improvement in the fatigue life of many metallic components. The process produces very little or no surface profile modification while producing a considerably deeper compressive residual stress layer than traditional shot peening operations. The work discussed here was designed to: (a) quantify the fatigue life improvement achieved by LSP in a typical high strength aircraft aluminium alloy and (b) identify any technological risks associated with its use. It is shown that when LSP conditions are optimal for the material and specimen configuration, a —three to four times increase in fatigue life over the as-machined specimens could be achieved for a representative fighter aircraft loading spectrum when applied at a representative load level. However, if the process parameters are not optimal for the material investigated here, fatigue lives of LSP treated specimens may be reduced instead of increased due to the occurrence of internal cracking. This paper details the effect of laser power density on fatigue life of 7050-T7451 aluminium alloy by experimental and numerical analysis.

Mechanical properties and energy absorption of ceramic particulate and resin-impregnation reinforced aluminium foams

The mechanical properties of aluminium foams can be improved by matrix reinforcement and resin-impregnation methods. In the present study, aluminium foams were reinforced by both ceramic particulate reinforcing of the aluminium matrix and resin-impregnating pores. The mechanical properties and the energy absorption of the reinforced aluminium foams were investigated by dynamic and quasi-static compression. Results indicated that the ceramic particle additions of CBN, SiC and B4C in aluminium foams increase the peak stress, elastic modulus and energy absorption of the aluminium foams, under both conditions of dynamic and quasi-static compression. Moreover, the aluminium foams with and without ceramic particle additions exhibited obvious strain rate sensitivity during dynamic compression. Furthermore, the resin-impregnation improves the mechanic properties and energy absorption of aluminium foams significantly. However, aluminium foams with resin-impregnation showed negligible strain rate sensitivity under dynamic compression. It is reported that both the ceramic particle addition and resin-impregnation can be effective techniques to improve the mechanical and the energy absorption properties of aluminium foams.

Crushing modes of aluminium tubes under axial compression

A numerical study of the crushing of circular aluminium tubes with and without aluminium foam fillers has been carried out to investigate their buckling behaviours under axial compression. A crushing mode classification chart has been established for empty tubes. The influence of boundary conditions on crushing mode has also been investigated. The effect of foam filler on the crushing mode of tubes filled with foam was then examined. The predicted results would assist the design of crashworthy tube components with the preferred crushing mode with the maximum energy absorption.