DOW 7 is typically used for both new and overhauled parts that has dissimilar materials where conditions will tolerate a less robust alternative than anodize coatings. This film is extremely thin and has very little corrosion resistance.  The primary purpose of these coatings is to form a film that will hold paint (allow paint to adhere to the magnesium part). Much like DOW 19, the DOW 7 is also a chromate chemical conversion coating.  Chemical conversion coatings, when applied to magnesium, have chemical reaction which results in a thin film being formed on the magnesium surface. DOW 7 also contains the toxic chemical hexavalent chromium (aka:Cr6+).  The primary drawbacks to these coatings are that they have little to no corrosion resistance.