Aluminium surfaces are often ‘anodized’. This means the deposition of a layer of

Anodizing of aluminium is an electrochemical surface treatment that thickens the naturally occurring oxide film on aluminium by making the part the anode in an electrolytic bath; the oxygen generated at the anode reacts with aluminium to form a thicker protective aluminium oxide layer (Al2O3) [1]. This anodic aluminium oxide coating is hard, wear- and corrosion-resistant, electrically insulating, and can be dyed for decorative finishes, which distinguishes anodizing from metal plating processes that deposit other metal oxides or metals. Therefore, anodizing deposits aluminium oxide on the aluminium surface, not chromium, nickel, or zinc oxides.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > p. 42