Although aluminium benefits from being extremely corrosion resistant, it can still tarnish, oxidise and corrode. The process of anodising enhances the natural corrosion resistance of aluminium as well as giving a much more consistent, aesthetic finish.
There are many ways to protect and enhance the appearance of aluminium but where anodising surpasses other aluminium surface finishes is that the process does not add anything to the metal, meaning that it remains 100% recyclable and 100% pure aluminium.
As the need for improved product durability, sustainability and attractiveness increases, anodised aluminium is becoming increasingly popular because if treated correctly, the finished metal can last a lot longer than untreated metal with minimal maintenance.
The anodising process
The process of anodising aluminium involves submerging the metal in an acid electrolyte bath and passing an electrical current through the solution. The bath has a cathode attached to it and the aluminium acts as the anode. When the electrical current is passed through, oxygen forms on the surface of the aluminium creating an aluminium oxide or ‘anodic’ layer. The quality of this anodic layer depends on many things including the temperature and concentration of the solution as well as the current passed through.
The thicker the anodic layer created, the greater the corrosion resistance and typically this layer is between 5 – 25 microns thick. The thickness of the layer is determined by the length of time the current is passed through the solution – the longer the metal spends in this state, the thicker the anodising layer.
After this first process of anodising, the anodic layer is very porous and so with the addition of dies, the final colour of the metal can be manipulated. Naturally, anodised aluminium is a matt, silver finish but with the addition of colour the range of possible finishes opens up.
The final stage in the process is to ‘seal’ the anodised aluminium. Because the surface of the metal is very porous, it is susceptible to outside elements such as dirt. There are different ways to seal the aluminium but each method closes the pores on the anodic layer making the final product much more corrosion resistant.
Grades to anodise
Although aluminium itself is ideal for anodising, different grades of aluminium react better to the process.
6063 is a very commonly anodised extrusion grade, which offers a good, consistent finish.
5000 series aluminium is the most commonly supplied anodised flat grade and supplied in sheet form.
J57 / J57s / J57s UP is a guaranteed anodising quality grade supplied in sheet and coil form specifically engineered so that the finish across each sheet is uniform. This grade is ideal for architectural applications where a uniform finish is paramount.
In addition to simply anodising, thyssenkrupp Materials can supply material that is sandblasted prior to anodising. This process gives a clean, consistent mechanical finish prior to undergoing the anodising process.
As important as design and mill selection is, the production process and packaging play just as vital a role. As the aluminium extrusion is produced, it is extruded out onto rolling tables and so it is important to specify any visible surfaces during the drawing process. The die can then be manufactured to help protect the visible surface as best possible.
The process of supplying a good anodised finish does not stop at production. The packing plays possibly one of the most important roles in ensuring damage free material. We can help you choose between tissue interleaved, plastic wrapped as well as bundle packing requirements.
thyssenkrupp Materials are experts in the supply of anodised aluminium and will help guide you through the process ensuring that you receive the correct, damage free finish for your application.