Surface Treatment of Aluminum - Why

As a result of its passive surface layer, aluminum alloys have a good corrosion resistance and a rather constant surface appearance. There are however some reasons, ex-emphfied in Table 37.4, for surface treatment of aluminum and its alloys. 

Improve surface appearance Anodizing (electrolytic oxidation) Anodizing and coloring Lacquering 

Increase surface hardness and wear resistance Hard anodizing 

Decrease the electrical transition resistance. Facilitate soldering Tinning 

Sealing of the pores is carried out in hot water after anodizing and coloring. In this process aluminum oxide on the inner sides of the pores swells to aluminum hydrox- 

---