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The variety of parts made from magnesium encompasses the entire industrial market.
 

 

 


MAGNESIUM CHROMIC TREATMENT                 SAE-AMS-M-3171 (supersedes Mil-M-3171)

Type I (Dow 1): A chrome pickle treatment for magnesium. Color varies from matte gray to yellow-red. Only fair corrosion resistance (less than 24 hours 20% salt spray resistance).  Removes metal (Approximately .0006" for wrought material, less for castings). No dimensional change. Used mainly for protecting magnesium during shipment, storage, and machining. Can be used as a paint base. Note: Must remove Type I coating before applying Type III and Type IV treatments. Good paint base and protective qualities for all magnesium alloys except EK30A, EK41A, EZ33A, HK31A and M1A

Type III (Dow 7): A dichromate treatment for magnesium. Color varies from light brown to dark brown to gray depending on alloy. Only fair corrosion resistance (less than 24 hours 20% salt spray resistance).Precleaning and pickling may result in dimensional changes due to metal loss.

Type IV (Dow 9): A galvanic anodize treatment for magnesium. Produces a dark brown to black coating. Designed to give a protective film on alloys which do not react to Dow No. 7 treatment. Only fair corrosion resistance (less than 24 hours 20% salt spray resistance). Makes no dimensional change. Can be used as a paint base, and is suitable to all magnesium alloys. Used where optical properties (black/non-reflective) are required on close tolerance parts (camera parts, laser components, telescopes, etc.) Note: Precleaning and pickling may result in dimensional changes due to basis material loss.

Type VI (Dow 19): Chromic Acid brush-on treatment. Touch up of abraded, damaged, or reworked areas previously coated with a chemical treatment such as Dow #7, or anodize is acceptable. Approval for reworking should be made on a part by part basis by the quality control department, and should be included in the processing specifications for each part number or family of part numbers. For instance, threads which have been reworked can often be repaired with a suitable cleaning and brush application of chromating solution. Type VII: Fluoride Anodizing

Type VIII: Chromate Treatment conversion coating

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