The Dow Chemical Company invented Dow 17, the first anodized magnesium coating, in the mid-1940’s. At that time, Dow Chemical Company was the world’s largest producer of magnesium. Dow 17 can be applied with either alternating or direct current. The electrolyte used to apply the coating is comprised of sodium dichromate, ammonium acid fluoride and phosphoric acid. The electrolyte has a pH of approximately 5 and should be operated at or above 160° F. The coating has little or no inherent salt spray resistance. On test plates made from alloys such as ZE41A, corrosion sites can be seen in as little as 48 hours. Dow 17 does provide good paint adhesion with the exception of migration from a scribe in salt spray. Corrosion can easily migrate in the very porous Dow 17 structure, even tunneling under the paint.
The Dow 17 coating can be applied as thin as 0.20 mil or as thick as 3.0 mil. The color of the Dow 17 coating varies between light and dark green depending upon coating thickness.