Is the whitening of aluminum profiles in humid conditions caused by rusting? An article to distinguish between aluminum corrosion and steel rusting
2026,07,21
Many users in daily life have noticed white powder on outdoor aluminum doors and windows, as well as aluminum brackets, and mistakenly believe that the aluminum is rusting. Here, I would like to correct a basic material common sense: strictly speaking, the concept of "rusting" does not exist for aluminum alloy.
Rust refers specifically to the oxidation of steel, resulting in the formation of reddish-brown iron oxide. When aluminum comes into contact with air, it automatically forms a dense aluminum oxide film, which naturally isolates the internal metal and provides basic corrosion resistance.
The appearance of white spots on the surface of profiles can be categorized into three types:
In salt spray/humid environments, the oxide film undergoes slight hydrolysis, resulting in the formation of white alumina powder, which often occurs on coastal profiles without fluorocarbon coating;
Electrochemical corrosion: When aluminum comes into direct contact with iron or copper hardware, a galvanic cell is formed in a humid environment, resulting in punctate white spots;
Strong acid and alkali cleaners damage the surface coating, revealing the underlying oxide layer.
Preventive measures: For outdoor high-humidity and coastal areas, opt for fluorocarbon coating; add insulating spacers to hardware accessories; use only neutral detergents to clean aluminum materials, avoiding bleach and strong alkaline cleaners, thereby eliminating the occurrence of white spots from the source.
