Aluminium Surface Finishes
In most scenarios, the natural finish and surface quality of aluminium can be used for many applications without any added surface finishing. However, there are cases in which aluminium requires different finishes. Finishes for aluminium are designed to either preserve an existing surface or promote a new surface that is more visually or functionally appealing. The primary reasons for a different surface finish could include aesthetic improvements, colour requirements, improved resistance, increased reflectivity, better surface structure and improved electrical insulation properties.
At Aluminium Trading, we offer a variety of different aluminium finishes, each with unique properties suited for specific applications.
As a metal, aluminium is susceptible to mechanical finishing processes commonly applied to other metals, and can usually be used with the same equipment without any disadvantage. However, to fully exploit the more unique characteristics of aluminium alloys, specialised equipment is desirable.
Generally, mechanical finishes apply processes which alter the metal by abrasion such as polishing, grinding, blasting, buffing or processes which apply the texture by mechanical force such as embossing or shot peening. When compared with steel, abrasive aluminium finishing processes need to take the relative softness of the aluminium into account, thus, lubrication and low application pressures are required.
A mill finish is the standard finish that aluminium has when it comes out of the mill. There is a wide range of uses and applications for a mill finish. This is the natural state of aluminium and no mechanical or chemical finishing has been added to the surface.
A Brushed Finish gives aluminium a distinctive look, as it retains some but not all of its lustre and is given a pattern of very fine lines parallel to the brushing direction. For this reason, it is commonly used in decorative applications.
Brushed finishes are popular in small appliances and whiteware, and feature largely in architecture and automotive design.
A Polished finish makes use of a mechanically abrasive process that creates a brushed or bright finish on the aluminium. Polishing is not a common process, but it presents different properties and benefits of aluminium. These include:
- Increased aesthetic appeal.
- Increased reflective properties.
- Reduce adhesion.
- Easier cleaning of the surface.
Chemical & Other Finishes
Chemical finishes rely on specific chemical reactions and are distinctive with aluminium. There are five principal classifications of chemical finishing
Chemical Cleaning – Treatments used to remove soils and oxides inhibitive to final finishing or other work operations.
Etching – Treatments designed to produce various degrees of surface mattness. Can also be a pre-treatment for other processes.
Chemical Brightening – Treatments designed to produce a high surface lustre.
Conversion Coatings – Treatments which promote surface films desirable for functional or aesthetic purposes.
Immersion Plating – Treatments which deposit a metallic surface coating.
Aluminium Trading offers the following chemical finishing options which may include one or more of the above-mentioned classifications:
In the pretreatment process, the aluminium is either etched or cleaned with an alkaline or acidic material before a pretreatment coating is applied. The applied coating enhances the adhesion of powder or paint and provides further resistance against corrosion.
Bright Dipping is an electro-brightening treatment that produces an extremely high lustre on aluminium. The bright dip process is always performed on raw aluminium and the harder tempered the alloy is, the brighter the resulting end product will be. Bright dip aluminium can achieve this high lustre by smoothening the aluminium surface at a microscopic level. It should be noted that bright dipping does not remove scratches or lines from the aluminium alloy.
When aluminium is exposed to air it immediately starts combining with the oxygen to form an inert protective layer of aluminium oxide. This layer of oxide is tiny, being only millionths of a centimetre thick.
Anodising is a method of creating a thicker layer of aluminium oxide to provide greater protection to the material. It is a controlled oxidation of the aluminium surface achieved by immersion in an electrolyte (usually diluted sulphuric acid) solution. Depending on the method, the original oxide layer will be removed from the aluminium before and a new oxide layer containing the desired colour and thickness will be applied.
Powder coating is a multi-stage process that creates a durable film or ‘coating’ on aluminium that can help meet stringent performance criteria. Furthermore, powder coating offers a virtually unlimited choice of colours and is very durable.
The aluminium to be coated is pre-treated in order to clean and prepare the surface to be sent through the spray booths. In the spray booths, an electro-statically charged powder is sprayed and attracted to the face of the aluminium to form an even coating. Once the aluminium is coated, it moves to a curing oven that melts or ‘cures’ the charged powder to form an even paint coating that adheres to the product’s surface. The generally recommended film thickness for powder coating aluminium is 60 microns.
Rigidised, Treadplate & Tread Bright
Our aluminium sheets can be supplied with a rigidised finish. Aluminium Trading stocks two standard patterns of rigidised sheet: 5WL (Rice) and 6WL Olive. Other patterns can be ordered on request (2WL, 10WG, 13SG etc.). Below are some visual examples showcasing our rigidised patterns and the difference between the Tread Bright and Treadplate patterns.