Aluminium coatings applications

Current usage is almost entirely associated with the good adhesion to aluminium. Specific applications include the bonding of aluminium foil to plastics films, as the adhesive layer between aluminium foil and polyethylene in multilayer extrusion-laminated non-lead toothpaste tubes and in coated aluminium foil pouches. Grades have more recently become available for manufacture by blown film processes designed for use in skin packaging applications. Such materials are said to comply with FDA regulations. 

Sprayed, vacuum-deposited and plated coatings can be applied to most metals and to many non-metals, e.g. vacuum deposition is applied to many substrates including plastics spray application can be used for coating fabric, plastic and paper. Hot dipping and other diffusion processes are dependent on the nature of the substrate for the properties of the coating. Most commercial applications of aluminium coatings are on iron and steel with smaller quantities applied to aluminium alloys and plastics. 

The non-toxicity of aluminium coatings and freedom from taste or taint means freedom from health hazards during application and provides hygienic finishes for contact with foodstuffs, e.g. baking tins, oven trays, containers. 

Matienzo, L. J. and Holub, K. J. Surface Studies of Corrosion-preventing Coatings for Aluminium Alloys , Applic. Surf. Sci., 9, 47-43 (1981)... 

Parylenes have also been used as an additional protective layer to the inorganic glass passivations used in semiconductor device fabrication. The main advantage of this extra coating is its ability to cover the normally exposed bond pad areas, giving protection to the exposed aluminium. Similar applications can also be envisaged for the coating of hybrid assemblies. 

Schematic of requirements for the transition from immersion experiments to industrial applications for aluminium. Coating formation has been divided into three types based on different physical and chemical processes to obtain the coatings. 

By a mechanism similar to that discussed in relation to platinum coating, titanium can function as a conducting jig to support aluminium components and assemblies in conventional anodising baths. In this application the exposed titanium acquires the insulating film, but allows current to pass to the aluminium at the points of contact . 

An interesting application of sprayed aluminium is for resistance to high-temperature oxidation up to 900°C. The article is grit-blasted and aluminium sprayed, usually to a thickness of 0-008 in (0-2 mm). It is then treated with a sealing composition which may be bitumen or water-glass, and is diffusion annealed in a furnace at 850 C for approximately 30 min. The final coating... 

Temperature resistance, i.e. a combination of melting point and oxidation resistance, may be of prime importance. A general correlation exists between melting point and hardness since both reflect the bond strength of the atoms in the crystal lattice, and the preferred order of coating metals for use in high temperature applications as temperature is increased is silver, aluminium, nickel, rhenium, chromium, palladium, platinum and rhodium. 

Experience in the application of metal-coating processes can materially affect economics. Thus, although it is possible to apply aluminium by... 

Cadmium also provides a sacrificial coating to steel which gives better protection than zinc in applications where strong acids and alkalis may be encountered and those involving immersion in stagnant or soft neutral waters. It should be used in applications involving bimetallic contact with aluminium and in electrical applications where ease of solderability is important. Cadmium has a low torque resistance and should be used as a coating material in cases where bolted assemblies have to be frequently... 

Spray-aluminised coatings are used for exhaust valves in automobile engines, exhaust and silencer systems (double and triple life), tyre moulds, gas ducting, heat-treatment pots, furnace ladles, carburising boxes and fans handling hot gases. Similar applications utilise Calorised and hot-dip aluminised coatings. Hot-dip aluminised steel wire has been used in steel-cored aluminium conductors for overhead transmission lines. For some... 

Resistance to abrasion The resistance to abrasion of electroless nickel-phosphorus hardened to 600 Hy, assessed by Taber abrasion tests, has been found to be double that of electroplated nickel However, electroless nickel coatings are not suitable for applications where two electroless nickel surfaces rub together without lubrication unless the values of hardness are made to differ by over 200 Hy units. Galling of aluminium, titanium or stainless steel may be overcome by applying electroless nickel to one of the two mating surfaces. 

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