What reason is white spot after aluminum oxidation

1, oxide film contaminated with impurities: oxide film in the formation process, may be contaminated with dust, insoluble impurities, acid or alkali and other substances, resulting in white spots on the surface. ‌

2, oil and corrosion: aluminum alloy surface contaminated with oil or other pollutants, or in the oxidation process by acid corrosion, will lead to white spots on the surface. ‌

3, moisture effect: too high humidity may lead to a decline in the quality of the oxide film on the surface of the aluminum alloy, which is easy to form white spots. ‌

4, alloying element segregation: in the extrusion and heat treatment process of aluminum alloy, if the alloying element distribution is not uniform, it may lead to intergranular corrosion, forming white flocculent AL(OH)3, and forming crystal spots after drying. ‌

5, alkaline corrosion treatment impact: In the alkaline corrosion treatment process, if improper treatment, may lead to the formation of a shallow and flat "corrosion pit" on the surface, resulting in white spots. ‌

6, sulfuric acid anodizing process impact: sulfuric acid concentration is too high, electrolytic temperature is not suitable or Al3+ content is too high, may lead to sulfuric acid oxidation tank Al(OH)3 flocculent precipitation and attached to the surface of the profile, forming white spots.