Universal Anodisers - Corrosion resistance in colour anodising for architectural aluminium

Anodising is an electro-chemical process used to create a protective film of aluminium oxide on the surface of aluminium extrusion or sheet. As the aluminium oxide film is created from the aluminium itself, it is integral to the aluminium and cannot crack or peel.   

Anodising is translucent giving the aluminium a deep metallic lustre and is extremely durable and continues to stand the test of time.

The unique anodised finish is the only one in the metals industry that satisfies each of the factors that must be considered when selecting a high performance aluminium finish:

Durability. Most anodised products have an extremely long life span and offer significant economic advantages through maintenance and operating savings. Anodising is a reacted finish that is integrated with the underlying aluminium for total bonding and unmatched adhesion.

Ease of Maintenance. Cleaning with mild soap and water will usually restore an anodised surface to its original appearance. Mild abrasive cleaners can be used for more difficult deposits.

Aesthetics. Anodising allows the aluminium to maintain its metallic appearance.

Cost. An initial finishing cost combined with lower maintenance costs for greater long-term value.

Health and Safety. Anodising is a safe process that is not harmful to human health. An anodised finish is chemically stable, will not decompose, is non-toxic.

Since the anodising process is a reinforcement of a naturally occurring oxide process, it is non-hazardous and produces no harmful or dangerous by-products.

Anodising enhances aluminium and its environmental virtues. Anodising uses the base metal - the aluminium alloy - to create a thin, extremely strong and corrosion-resistant finish.  The anodised surface is very hard and thus preserves and extends the life of the aluminium product.

In contrast to anodising, coatings - paint for example - can dramatically reduce the ability to recycle the aluminium and can increase costs.  Paints, plastics, and plating rely on problematic materials in their production that can compromise green objectives.  Anodising, on the other hand, is "recycle-neutral" with minimal use of such materials as volatile organic compounds and heavy metals.

The purpose of anodising is to form a layer of aluminium oxide that will protect the aluminium beneath it. The aluminium oxide layer has much higher corrosion and abrasion resistance than aluminium.

The anodic oxide structure originates from the aluminium substrate and is composed entirely of aluminium oxide. This aluminium oxide is not applied to the surface like paint or plating, but is fully integrated with the underlying aluminium substrate, so cannot chip or peel. It has a highly ordered, porous structure that allows for secondary processes such as colouring and sealing.

Anodising is accomplished by immersing the aluminium into an acid electrolyte bath and passing an electric current through the medium. A cathode is mounted to the inside of the anodising tank; the aluminium acts as an anode, so that oxygen ions are released from the electrolyte to combine with the aluminium atoms at the surface of the part being anodised. Anodising is, therefore, a matter of highly controlled oxidation—the enhancement of a naturally occurring phenomenon.

The aluminium is clamped onto racks and chemically etched before anodising to remove minor surface imperfections and to create our smooth satin finish.

We have 18 exclusive colours, these colours are broken into two categories - Electro Colouring or Interference Colouring

To view the colours available – click here

Electro Colouring - After anodising, the metal is immersed in a bath containing inorganic metal salt. When current is applied metal salts are deposited into the base of the pores.  This process offers colour versatility and the most technically advanced colour quality, from sandstone to dark bronze and black.

Interference colouring – An additional colouring procedure, involves modification of the pore structure. The colours are caused by optical interference rather than light scattering as with the basic electro-colouring. 

The colour perception is a result of an optical illusion.  White light can be dispersed into its colour bands by a prism.  The various spectral colours arise.

Optical refraction, diffraction and reflection of white light causes an interference between the electromagnetic wavelengths of the light spectrum.  This interference may result in the absorption of superimposition of wavelengths – and a colour being perceived. 

The modification can be either achieved by applying an additional electrochemical process with special additives in a separate tank or by using an advance power supply and controller system that does not require any additional process tank.

Various theories explaining what happens to the oxide layer during the modification step are readily available.

Another theory is derived from TEM results produced by an electrical modification system.  A ‘second barrier’ is formed at a certain distance to the initial barrier layer.  In the next step a metal salt is deposited in the pore and the incoming light then passes a metal filter, generating an interference effect and thus creating a new colour perception.

In summary the term ‘interference colouring’ in fact describes the optical phenomena taking place in the oxide layer to create an interference effect.

Our interference colours include Azure, Reef and Steel Blue, Sage Green, Gum Tip, Stainless, Silver, Slate and Charcoal Grey.

For more information on Interference colour please contact us at Universal Anodisers.

The aluminium oxide surface is the same material as sapphire or carborundum and provides a hard, wear-resistant and weather-resistant surface for architectural aluminium products. 

The accompanying test sheets illustrate hardness comparisons – See test results below

Thicknesses from 10 microns to 25 microns are available, giving the required degree of wear and corrosion resistance from internal to severe external applications.  At 25 micron the aluminium is impervious to salt.  See test results below.

An essential factor in corrosion resistance and colour durability is sealing.  This quality is reflected in corrosion and silicon adhesion tests.  Clear anodising, no colour and black anodising, the darkest colour , were both tested for silicon adhesion and showed 100% adhesion before and after water immersion.

See test results below.

To maintain the decorative and protective properties of anodising against atmospheric pollutants and grime, a regular cleaning schedule should be specified and adhered to.

The preferred method of cleaning anodised aluminium is warm soapy water, gently rubbing with a damp cloth or sponge until any grime is removed.  It is important to rinse thoroughly with fresh water to remove any traces of detergent. 

Acid or alkaline cleaning compounds should be avoided as they may attack the anodic surface.  Abrasive cleaners should not be used.

Anodising Thickness & Cleaning Frequency

Severe or very severe interior conditions could result from moisture condensation, such as in indoor pools.
Severe or very severe exterior conditions could result from a coastal site exposed to salt water vapour.

Contact with highly abrasive materials such as sandpaper should be avoided.

Contact with alkaline products such as the mortar used in cement rendering, plastering and tiling must be avoided totally and any traces should be removed from any anodised surface immediately.
It is important to mask the aluminium prior to any alkaline coming into contact  with the anodised aluminium

Hardness Tests
Metallurgical testing has confirmed that Universal Hardcoat is up to twice as hard as stainless steel
– important wherever abrasion is a consideration.
To view a report summary, click here.

Sealing Tests
Examination of Universal Hardcoat samples indicated sealing of the highest quality.
To view a report summary, click here.
 

Ultraviolet Tests
Accelerated UV irradiation testing has confirmed Universal Hardcoat is virtually unaffected
by the equivalent of 50 years of Sydney (Australia) UV exposure.
To view a report summary, click here.

Corrosion Tests
Salt spray testing has confirmed that 25 micron Universal Hardcoat is virtually unaffected
by exposure to salt spray corrosion.
To view a report summary, click here.

Aluminium Life Cycle Enhancement with Anodising
The environmental advantages of aluminium are widely acknowledged.  Aluminium is one of the most durable and versatile of metals. It’s lightweight and has 100% recyclability. 

Anodising enhances aluminium and its environmental virtues. Anodising uses the base metal - the aluminium alloy - to create a thin, extremely strong and corrosion-resistant finish that will not crack or peel.  The anodised surface is very hard and thus preserves and extends the life of the aluminium product.

In contrast to anodising, coatings - paint for example - can dramatically reduce the ability to recycle the aluminium and can increase costs.  Paints, plastics, and plating can compromise green objectives.  Anodising, on the other hand, is "recycle-neutral".

Recyclability is unaltered by anodising and no intermediate processing is needed for anodised metal to re-enter the recycle chain, unlike painted or plated metallic coatings.

Anodised aluminium is the environmentally sound choice for various applications.

Universal Anodisers is conscious of their environmental responsibilities.  Management is constantly looking at ways to improve its processes and at the same time reduce their impact on the environment. We joined a group of other local businesses with Fairfield City Council and the local Smithfield / Wetherill Park Chamber of Commerce on a Cleaner Production Project.  With support from the Council and specialist environmental consultants, Universal Anodisers established its own cleaner production team, bringing together staff from across the business to identify and implement plans for improving the plant’s environmental performance.

One of the outcomes of the analysis was to outlay a large investment initially that would significantly reduce our water and electricity consumption. This has been successfully accomplished.

The company’s objectives has exceeded its initial expectations and progress reviews, maintaining our environmental obligations.

Warranties are available upon application for the integrity of the anodising