Mill Finish is a basic finish of aluminium extrusion products, it has not gone through further mechanical or chemical process. Aluminium in general has high resistance to corrosion, because it is spontaneously covered by a thin layer due to the result of oxidation that makes the product more durable. The surface of mill finished products appear rugged without any surface treatment.
Powder Coating process is done electrostatically by spraying dry powder to the mill finish product without using any catalyst. Powder coating finish has no sagging mark. The advantages of using powder coating are increased tensile and scratch resistance, increase weather resistance, and the profiles are available in a wide variety of colors.
Anodize finish allows aluminium extrusion to be more corrosive resistant compared to Mill Finish. Anodising is essentially a process where a thick film of aluminium oxide is built up on the surface of the aluminium through the use of a direct current electrical supply. After anodising the surface may be coloured by an electrolytic method using appropriate metal cations, and then sealed by placing in boiling water, the pores in the oxide layer being closed off.