Hard Sulfuric Anodizing

Hard sulfuric acid anodizing is commonly called hard-coat or hard sulfuric anodizing. This Type 3 anodize, as designated by the Mil-A-8625 standard, results in superior hardness, abrasion, and corrosion resistance compared to other types of anodize. Due to the thickness of the coating, hard anodized parts provide an elevated level of wear and corrosion resistance over regular anodizing while still maintaining the ability to retain the dye, leading to many exterior gun components utilizing this process.

Advantages of Hard Anodizing

The AMS 2469 and ASTM B580 specifications also cover hard sulfuric anodizing. Hard anodize is processed in a refrigerated tank at higher voltages than other anodized coatings. Depending on the alloy of aluminum and the thickness of the coating, the natural color will vary from a tan or dark gray to almost black. It can also be dyed in a variety of colors. 

Hard anodized coatings are usually thicker than .001 and will change the dimensions of a part by 50% of the total thickness of the deposit (50% penetration and 50% buildup). After sulfuric anodizing, hard anodize solutions may be sealed in hot water, sodium dichromate, nickel acetate, dewatering oil, wax, or PTFE solutions.

Industries That Utilize Hard Sulfuric Anodizing

Many military contracts require precise hard anodizing, using X-ray machines to certify that the coating thickness conforms to the military specification for government use. You will commonly see frames, receivers, and handguards with hard anodized coatings, as well as small accessory components like rails and plates.

To learn more about our anodizing processes, please contact us at Silvex today.