Aluminium surface preparation

Mori, S., Suginoya, M. and Tamai, I. (1982) Chemisorption of organic compounds on a clean aluminium surface prepared by cutting under high vacuum, ASLE Trans. 25 261-266. 

The painting procedure for other metal surfaces, although similar, the process of pre-treatment for cast iron components or non-ferrous metals, such as aluminium and copper, may need more care. The process of pre-treatment in such cases may vary slightly than for MS, as noted below. Such surfaces may require a change in the type of chemicals, their concentration and duration of treatment. The final surface preparation and painting procedure, however, will remain the same for all. 

Remarkably uniform MgO smoke was prepared by Coulomb and Vilches (1984) by burning magnesium ribbons in dry OjAi mixtures. The MgO particles were collected in die form of a coating on a clean aluminium surface and were subjected to heat treatment (at c. 950°C and pressures < 10 6 mbar). The specific surface area of the final MgO(l 0 0) powder was c. 8 m2 g-1 so that it was not difficult to undertake accurate physisorption measurements and also neutron scattering experiments. 

Growth stresses in the oxide may also contribute. Wrinkling is affected by the more rapid diffusion of nickel into the coating from the substrate compared to the inward diffusion of aluminium and it is also dependent on the initial surface preparation of the coating with smoother coatings being less susceptible. 

Similarly, with aluminium honeycomb structures, failure may occur at the skin or the surface of the honeycomb itself, especially if the respective surface preparation is poor (see Pre-treatment of aiuminium). Untreated aluminium alloy honeycomb can result in disbonding in service. The use of anodized aluminium alloy honeycomb is strongly recommended. 

There are many references in the literature to this method of surface preparation of aluminium. The name refers to the US Forest Products Laboratory, which published a specification based on etching the metal at c. 65 °C in a solution of sodium dichromate and sulphuric acid, sometimes loosely referred to as chromic acid . In the United Kingdom, a similar Ministry of Supply Aircraft Process Specification known as DTD 915 has been widely used. Over the years, a number of slightly different solutions ( chromic acid etches ) and procedures have been developed. Clearfield gives recipes for six such solutions. ... 

More recently, as much more sophisticated techniques of Electron microscopy have been developed for examining the features of surfaces, Venables and his colleagues have revealed the detailed morphology of aluminium surfaces that have been prepared by various well-established techniques for adhesive bonding (see Anodizing, FPL etch. 

Importantly, for a particular application, and where the metals to be joined have been specified, an overall metal bonding system should be considered. Typically, this will include selection of a suitable adhesive and possibly primer or coupling agent in combination with appropriate methods of surface preparation or pre-treatment. Organofunctional silanes (see Silane adhesion promoters) are commonly used coupling agents, which have been demonstrated to provide covalent chemical bonds with steel or aluminium surfaces and possess epoxide or amine functionality for reaction with Epoxide adhesives. 

The clean appearance of an aluminium surface is very deceptive it is actually composed of a thin layer of oxidation products, invisible to the unaided eye, which forms a weak link between the true aluminium surface and the adhesive. Although the oxide films on some alloys is reasonably stable, and gives fairly robust joints with some adhesives without preparation, this must not be generally assumed but should be checked and evaluated. Failure to remove a weak oxide layer will always result in a weak joint. 

Despite the copious evolution of phenol and water during processing, Narmco s commercial adhesive system (Imidite 850) was based on prepolymer 28 mixed with aluminium powder, inorganic arsenic compounds such as arsenic thioarsen-ate or arsenic pentasulphide, and sterically hindered polyphenol antioxidant. Adhesive tapes were manufactured hy hot-melt deposition of this mixture on a 112-type glass cloth carrier used in conjunction with a heat-resistant primer (polybenzimidazole or polyimide). As with all other heat resistant polymers, surface preparation of flat and honeycomb metal surfaces is an important factor in... 

ASTM D 2674-72 (1984) Methods of Analysis of Sulfochromate Etch Solution Used in Surface Preparation of Aluminium. 

ASTM D 3933-80 Practice for Preparation of Aluminium Surfaces for Structural Adhesives Bonding (Phosphoric Acid Anodising). 

Aluminium alloy Surface preparation and time of immersion in CeCh Time (days)... 

For aluminium alloys, there are three common surface-preparation... 

This procedure has been used for several years to prepare aluminium surfaces for painting. Even in an unsealed state, it was not generally thought that the oxide film produced, which is extremely dense, was suitable for either structural or semi-structural adhesive bonding although its corrosion resistance was known to be exceptional. It is a modem adaptation of the standard procedure which is now of interest to stractural adhesive bonders. 

Campestrini, R, van Westing, E.R.M., and de Wit, J.H.W., Influence of surface preparation on performance of chromate conversion coatings on Alclad 2024 aluminium alloy Rart I Nucleation and growth. Electrochimica Acta, 2001. 46(16) 2553-2571. 

The lap joint, in which two sheets are joined together with an overlay, is one of the most common joints encountered in practice. Joints of this type made from thin aluminium sheet 25 mm wide, 12 mm long (lin by 0-5 in) and 1-6 mm thick have long been used for quality control. The joint is easy to make and the results are sensitive to both adhesive quality and adherend surface preparation. 

Epoxy resins give an excellent bond with a properly prepared aluminium surface. This has led to the use of aluminium powder as a filler for epoxide resins, giving an example of a filler which enhances tensile shear strength both at room and at elevated temperatures. 

Item (iv) concerns corrosion inhibition. The reagents most commonly employed are strontium or zinc chromates. As only those particles in direct contact with the steel or aluminium surface are effective inhibitors, it is reasonable to apply them in a suitable binder in as thin a layer as possible. Etch primers, such as are used in paint technology, are unsuitable for use with adhesives and the etching must be carried out as a separate operation as has been discussed in detail above. Where a chromic acid process has been used to prepare the surface, some chromate becomes incorporated therein and the use of a chromate-containing primer seems superfluous. 

Allen KW (1977) Surface preparation of a stainless steel for adhesive bonding. J Adhes 8 183 Arrowsmith DJ, Clifford AW (1985) A new pretreatment for the adhesive bonding of aluminium. Int J Adhes... 

The required surface preparation depends on which substrate will be bonded and which kind of adhesive is applied. Some metals, for example, have oxide layers like aluminium, magnesium, or titanium. In this case, the surface preparation focuses on stabilizing the oxide layer. 

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