The primary difference between Alodine (chem film) and anodizing is that anodizing is an electrolytic process and Alodine (chem film) is not.
Alodine (chem film) and anodizing are both processes used in aluminum finishing to improve corrosion resistance. Both transform the outer layer of the surface of the metal.
But Alodine (chem film) and anodizing are NOT the same.
Anodizing is an electrolytic finishing process that applies electrical current to the metal while it is immersed in an electrolyte solution. In addition to increased corrosion resistance, aluminum anodizing is used for improved lubrication or to allow dyeing (coloring). It is generally more expensive to anodize than to apply chem film and requires greater technical expertise.
In contrast, Alodine (chem film) coatings do NOT apply electrical current to the aluminum. The metal is immersed in a tank, often at room temperature. Compared to anodizing, chem film is less expensive and requires less technical expertise. Unlike anodizing, a chem film coating can allow aluminum to retain electrical or thermal conductivity. This makes chem film the preferred choice when aluminum parts need to be electrically grounded.