Surface treatments may need to be carried out on extruded parts for a variety of reasons. This may be to alter the colour of the extrusions, to increase hardness or reduce friction, provide resistance to wear, or to enhance the surface finish.
Once the production of extruded components is complete, it is not uncommon for them to be sent to a finishing specialist to have any number of surface treatments carried out. Common examples include polishing, powder coating, anodising, hard anodising and screen printing.
A finishing specialist will be able to work with you to determine which surface treatments are required based upon the desired end result. However, it's worth noting that some surface treatments may only be able to be carried out on certain materials - for instance, anodising is especially well-suited to aluminium.