Aluminium alloys are Anodised to increase corrosion resistance, to increase surface hardness, and to allow dyeing (colouring), improved lubrication, or improved adhesion. The anodic layer is non-conductive.
When exposed to air at room temperature, or any other gas containing oxygen, pure aluminium self-passivates by forming a surface layer of amorphous aluminium oxide 2 to 3 nm thick, which provides very effective protection against corrosion. Aluminium alloys typically form a thicker oxide layer, 5-15 nm thick, but tend to be more susceptible to corrosion. Aluminium alloy parts are Anodised to greatly increase the thickness of this layer for corrosion resistance. The corrosion resistance of aluminium alloys is significantly decreased by certain alloying elements or impurities: copper, iron, and silicon, so 2000, 4000, and 6000-series alloys tend to be most susceptible.
You will see anodised aluminium on aircraft parts, architectural materials, and various consumer products such as, mp3 players, flashlights, cookware, cameras, sporting goods, window frames, roofs, in electrolytic capacitors, and on many other products. Although anodizing only has moderate wear resistance, the deeper pores can better retain a lubricating film than a smooth surface would.
Anodised coatings have a much lower thermal conductivity and coefficient of linear expansion than aluminium. In typical commercial aluminium anodisation processes, the aluminium oxide is grown down into the surface and out from the surface by equal amounts. Anodising will increase the part dimensions on each surface by half of the oxide thickness. For example a coating that is (2 microns) thick, will increase the part dimensions by (1 microns) per surface. If the part is Anodised on all sides, then all linear dimensions will increase by the oxide thickness. Anodised aluminium surfaces are harder than aluminium but have low to moderate wear resistance, although this can be improved with thickness and sealing.
Anodising, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called “anodising” because the part to be treated forms the anode electrode of an electrical circuit. Anodising increases corrosion resistance and wear resistance. Anodic films can be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light. Anodising is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminium alloys, although processes also exist for titanium, zinc, magnesium, niobium, and tantalum. This process is not a useful treatment for iron or carbon steel because these metals exfoliate when oxidized; i.e. the iron oxide (also known as rust) flakes off, constantly exposing the underlying metal to corrosion.
Anodising changes the microscopic texture of the surface and changes the crystal structure of the metal near the surface. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodised aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from aging and wear, but more susceptible to cracking from thermal stress.
Electroplating is the process of depositing a metallic coating upon a negatively charged electrode by the passage of an electric current. The purpose of electroplating is to obtain a metallic coating having different properties or dimensions than those of the basis metal. For example, a harder, brighter or more corrosion resistant metallic coating may be deposited over the basis metal.
The requirements are: A source of direct current, a container holding a plating solution in which is dissolved a salt of the metal to be plated, a positive electrode, (anode) and a suitably prepared object to be plated as the negative electrode (cathode).
The Plating Metals
Most electroplating coatings fall into one of the following three categories:
Used primarily for protection of the basis metal, usually iron and steel (sometimes call anodic coatings, meaning that electrochemically they are anodic to the substrate). Sacrificial denotes that the coatings “sacrifice” themselves in the act of protecting the basis metal.
Zinc is primarily used for this purpose. Cadmium to a limited extent.
Decorative protective coatings
Used primarily for adding attractive appearance to some protective qualities.
Gold, silver, copper, nickel and chromium are commonly used.
A rather miscellaneous group whose members are used for specific properties imparted to the surface, such as solderability, wear resistance, reflectivity, conductivity, and many others. They are sometimes called functional coatings, though it would seem that protection is also a “function”.
‘Hard chrome’ (a thick deposit of chrome), tin (solderability), gold and silver (conductivity) and nickel.
It is common to use copper and or nickel as base deposits for other plated metals to improve adhesion and other properties. The plated article is often further protected against wear or corrosion by being chemically treated (passivated) or lacquered.
What is Powder Coating?
Powder Coating is a dry process by which selected items are coated with ground up paint particles in powder consistency then cured by heat to form a skin. Powder is a high quality finish found on thousands of products you come into contact with each day such as household appliances, furniture, automotive and playground equipment and is used as a functional, protective coating as well as a decorative finish.
Powder Coating has proved to be more durable than conventional paint, and is available in virtually an unlimited array of colours and textures. Texture selections range from smooth surfaces to wrinkled, and rough textures are available for hiding surface imperfections. Thick coatings can be achieved quickly and efficiently.
Many companies specify powder for its high-quality durable coating, improved efficiencies and excellent performance properties.
Durability of Powder Coating
The Powder Coating creates a hard finish that is tougher than conventional paint and is durable enough for the rigors of industrial applications.
Powder coatings have been shown to possess significant durability and resistance to abrasion, corrosion, scratching, and chemicals when compared to liquid coatings. It protects the toughest machinery as well as the household items you depend on daily, while still providing an attractive finish.
Powder coating is extremely resistant to moisture and heat and can withstand a large range of temperatures, and extreme weather conditions. Powder coated aluminium parts won’t rust and carry a lifetime warranty.
Advantages of Powder Coating
Durability – Powder Coating provides a more durable coating than conventional paints, whilst providing an attractive finish which lasts a long time.
Lower Reject Rates– Powder coating does not run, drip or sag, therefore creating fewer rejects.
UV Protected – Powder Coating is resistant to Ultra Violet light, colours stay bright and vibrant.
Environmentaly Compliant – The powder coating process is virtually pollution free making it an environmentaly preferred coating.
Cost Effective – Powder coating gives consumers, businesses, and industry one of the most economical, longest-lasting, quality finishes available. Evidence shows that powder coatings maximize production, cut costs and improve efficiencies – factors all related to the end-user’s bottom line.
Environmental impact of Powder Coating
Powder Coating is a clean process. Environmental advantages have led the way for the conversion of liquid coatings to powder coatings.
Pollution Free – Powder coating contains no solvent, and thereby the process emits negligible, if any, polluting volatile organic compounds (VOCs) into the atmosphere.
Energy Efficient – Exhaust air from the coating booth, can be returned to the plant requiring less heating and cooling of outside air to supply oven exhaust air.
Recyclable – Powder coating over-spray can be retrieved and re-used.
AISF membership serves as a fantastic opportunity to be part of a leading industry association and provides an enviable platform to be recognised as an industry leader amongst your peers Australia wide.