Home arrow News arrow Surface Treatment Of Aluminum And Aluminum Alloys, with examples
Surface Treatment Of Aluminum And Aluminum Alloys, with examples

Surface Treatment Of Aluminum And Aluminum Alloys

Key to Metals
Aluminum alloys are divided into two categories
  • wrought alloys
  • casting alloys.
A further differentiation is based primary on mechanism of property development. Many alloys respond to thermal treatment based on phase solubility. These treatments include solution heat treatment, quenching and precipitation, or age hardening.

In order to improve the surface properties of final products of aluminium alloys, such as corrosion resistance, wear resistance,  reflectivity etc., different types of surface treatment were designed. All of them are divided into the following groups.

Chemical treatment


Chemical brightening

Chemical treatment to improve the optical reflectivity of a surface.

Chemical polishing
Polishing of a metal surface by immersion in a solution of chemical reagents.

Degreasing

Removal of oil or grease, usually by a suitable organic solvent or an aqueous detergent.

Etching
Roughening of the surface of a metal by overall or selective dissolution in acid or caustic media.

Pickling

Removal of a thin surface layer of a metal by chemical action, mainly by treatment in a caustic solution.

Electrochemical treatment


Electrochemical brightening
Electrochemical treatment to improve the optical reflectivity of a surface.

Electropolishing

Polishing of a metal surface by making it anodic in an appropriate electrolyte.

Anodized metal
Metal with an anodic coating, produced by an electrolytic oxidation process in which the metal is converted to a mainly oxide coating having protective, decorative or functional properties.

Clear anodized metal
Metal with a substantially colorless, translucent anodic oxidation coating.

Color anodized metal

Anodized metal colored either during anodizing or by subsequent coloring processes.

Integral color anodized metal
Metal that has been anodized using an appropriate (usually organic acid based) electrolyte which produces a colored coating during the anodizing process itself.

Electrolytically colored anodized metal
Metal with an anodic oxidation coating that has been colored by the electrolytic deposition of a metal or metal oxide into the pore structure.

Dyed anodized metal
Metal with an anodic oxidation coating colored by absorption of dye-stuff or pigments into the pore structure.

Combination color anodized metal

Metal with an anodic oxidation coating that is colored by electrolytic coloring or produced by integral color anodizing followed by absorption dyeing.

Interference color anodized metal

Metal with an anodic oxidation coating colored by means of optical interference effects.

Bright anodized meta

Anodized metal with a high specular reflectance as the primary characteristic.

Protective anodizing

Anodizing where protection against corrosion or wear is the primary characteristic and appearance is secondary or of no importance.

Decorative anodizing
Anodizing where a decorative finish with a uniform or a esthetically pleasing appearance is the primary characteristic.

Architectural anodizing

Anodizing to produce an architectural finish to be used in permanent, exterior and static situations where both appearance and long life are important.

Hard anodized metal

Anodized metal on which the anodic oxidation coating has been produced with wear and/or abrasion resistance as the primary characteristic.

Sealing
Treatment of anodic oxidation coatings on metal to reduce porosity and the absorption capacity of the coating by hydrothermal processes carried out after anodizing.

Cold impregnation

Treatment of anodic oxidation coatings on metal to plug the pores and reduce the absorption capacity of the coating by chemical processes carried out at low temperatures after anodizing.

Significant surface

The part of the product covered or to be covered by the coating and for which the coating is essential for serviceability and/or appearance.


Coating

Coating (organic)
Method in which a coating material is applied on a metallic substrate. This process includes cleaning and chemical pre-treatment and either:
  • one-side or two-side, single or multiple application of liquid or powder coating materials which are subsequently cured, or
  • laminating with plastic films.

Coil coating

Continuous coating of a metal strip.

Backing coat

Single coating of any type with no particular requirements for appearance, malleability, corrosion protection, etc. usually on the reverse side of the coated product.

Chemical conversion coating
Treatment of a metal with chemical solutions by dipping or spraying to build up an oxide film containing chromates or phosphates.

Priming
Application of a priming paint often pigmented with a corrosion inhibitor such as zinc chromate, after suitable pretreatment.

Pretreatment priming
Application of a solution containing a resin, a chromate and an acid, which is allowed to dry on and provide the key for subsequent painting.

Single coat system
Single coating either with requirements on appearance, malleability, corrosion protection, subsequent painting, etc., or as a primer with special properties regarding adhesion and corrosion protection for post-painting applications.

Multiple coat system
System comprising a primer or a base coat, possibly intermediate coat(s), and a top coat with particular requirements on appearance, malleability, corrosion protection, etc.

Organic coating

Dry paint film of the coated product or the organic film metal laminate.

Film coating
Organic film applied to a substrate to which an adhesive and, if appropriate, a primer has been applied beforehand.

Lacquering
Coating with a formulation based on a dissolved material which forms a transparent layer primarily after drying by evaporation of the solvent.

Painting

Coating with a non-transparent formulation containing pigments.
   

Nonchemical Surface Treatment for Aluminum Alloys

Gerhardus H. Koch; Gary L. Todd; Arnold Deutchman; Robert Partyka; CC TECHNOLOGIES LABORATORIES INC DUBLIN OH
The state-of-the-art chemical surface treatments for adhesive bonding of aluminum alloys, such as phosphoric acid anodizing (PAA) are the basis of the present high-strength and durable adhesive bonds. Because of increasingly strict regulations on the use of wet chemicals, the Materials Directorate at Wright Laboratories initiated a research program to develop alternative nonchemical techniques that do not produce waste and are not detrimental to health and environment. This report describes the development of a nonchemical process, based on ion beam enhanced deposition (IBED). The process consists of various steps, the major ones being grit blasting with 50 micrometers Al2O3 grit and deposition of (proportional to) - Al2O3 with IBED. The resulting surface is dense and corrosion resistant, and provides an excellent basis for adhesive bonding. Strength and durability studies on peel and wedge type specimens is equivalent to that of anodized specimens. Surface analytical studies, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) , and Atomic Force Microscopy (AFM), as well as electrochemical studies were used to characterize the surface and determine the mechanism of adhesion.

Excimer laser surface treatment of aluminum alloy AA7075 to improve corrosion resistance.

T. M. YueCorresponding Author Contact Information, E-mail The Corresponding Author, a, L. J. Yana, C. P. Chana, C. F. Donga, H. C. Mana and G. K. H. Pang
Excimer laser surface treatment was found to be an effective method for improving the pitting corrosion resistance of the aluminum alloy 7075. The results of the TEM study showed that laser surface melting of the alloy at an intensity of 10.3 J/cm2 resulted in the elimination of coarse second-phase particles in the laser-melted zone. More importantly, two compact layers containing aluminum oxide were formed on top of the laser-melted surface. Potentiodynamic polarization tests showed that as a result of the laser treatment, the corrosion current can be reduced by as much as six times, and a passive region was obtained. Besides, the analysis of the electrochemical impedance measurements showed that at an open-circuit potential (OCP), the polarization resistance and double-layer capacitance of the film/electrolyte interface of the laser-treated specimen were one order of magnitude higher and six times lower than that of the untreated specimen, respectively. Furthermore, when tested at OCP+50 mV, the untreated specimen suffered serious pitting corrosion, while a passive film had formed on the laser-treated specimen, which served as an effective barrier for reducing anodic dissolution.