What kind of surface treatment to choose? (Topic: 14001)

Within the main groups of surface treatment there are many kinds to choose. Sometimes is the decision made by the builder or the architect. Other times the service condition or the price determines the surface treatment.

Properties of the different surface treatment processes

The various surface treatment methods have different properties, some advantageous, and some detrimental. The main properties for the various methods are as follows:

Anodising

Advantages:

1. Retention of the metallic appearance of aluminium (natural anodising)

2. Better wear resistance than lacquer coatings

3. Better corrosion resistance than lacquer coatings

4. Ability to colour the anodic oxide film with a wide range of colours

5. Some fire protection

6. High electrical resistance

Disadvantages:

1. White colouring (in the normal way) of the oxide layer is not possible

2. Possibility for uneven colour over the jig, or across a profile

3. Limited colour selection for exterior application

Lacquering

Advantages:

1. A wide range of colours are available

2. Gives a good weather and corrosion resistance

3. Gives an even colour across a profile, and over the whole surface of profiles

4. Masks irregularities in the profile surface

Disadvantages:

1. Lesser wear resistance than anodised surfaces

2. The metallic aluminium appearance is hidden (but metallic finishes possible)

3. Lesser corrosion resistance than anodised surfaces

4. No fire protection; dangerous gases could be evolved during a fire

5. Scratches through the coating can easier be made than on anodised surfaces, which

could provide sites for corrosion attack

6. Limited throwing power into channels with electrostatic spray system

Plating

Advantages:

1. Improvement of the decorative appearance (after polishing)

2. Improvement of the wear and corrosion resistance, and hardness

3. Improvement of the soldering/brazing ability

Disadvantages:

1. More expensive than lacquering and anodising

2. Requires pre-treatment (e.g. zincating and polishing)

3. Electrolytic processes give variable thicknesses of the plated metal dependent of

the geometry of the profile.

4. Most plated coatings on aluminium will be cathodic (more noble) in relation to

aluminium. Defects in such coatings can cause severe corrosion attacks dependent

on the environment.